Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: SkipJohnson on February 14, 2019, 11:12:29 am
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I have been building tube amps over the last year and a half. All my builds (10 vintage style tube amps including 2 Champs, 4 Princetons, 1 Bassman, 1 Deluxe, 1 Stereo Champ and a Fender Reverb Unit) have been based on Fender designs. I have decided my next build needed to be something different and I decided on a British design this go. I came across Sluckey's 1960 Vox AC15 site (sluckeyamps.com) and decided this was the right build for me to take on. Further research on this build has lead me here.
I have been researching this build for a while and have collected as much documentation as I could find including the documentation from Sluckey's 1960 Vox AC15 site as well as here on the Hoffman Amp site. I have found some discrepancies between the documentation (slight design differences, Mod's, BOM lists, etc..) so my first goal is to have a complete set of design documentation and vet it here on the forum before building. I am hoping some of you can help me fill in the gaps of my documentation.
I want to procure/develop the following design documentation:
NOTE: I would love to get Visio (.vsd) or DIY Layout Editor (.diy) files for these if anyone has them. I could then maintain my own version as I make slight changes along the way.
Schematic - I have two (2) versions that are but these are workable so I am good here.
Power Section Chassis Layout - I could not find anything for this. This design is pretty different from my Fender builds so this is important because I have never included a standby switch or used this type of rectifier in any of my builds. I created my own version(s) for this using Visio. I have two versions based on some differing documentation I have. I will share these to get your input.
Grounding Scheme Diagram - I have Sluckey's design to use. I may also use isolated input jacks as they have been very good in reducing noise in my prior builds. I will look forward to input from you all on this subject.
Circuit Board Layout - I Sluckey's design to use. I would really like a Visio or DIY file for this.
Circuit Board Blueprint - I Sluckey's design to use. I also purchase the completed board with turrets from the Hoffman Amp site. I just need to drill the mounting and wire-thru holes.
Complete Chassis Layout Diagram - I usually create a compete Chassis Layout that includes everything (power section, grounding, circuit board, controls, etc.) I would love to get one if anyone has one, or I may create one myself.
Chassis Blueprint - I am comfortable doing this on my own as I have done many.
BOM (Parts List) - The two BOM lists I have found are slightly different. I will create my own version of this as I get the documentation put together.
Here is where I am at on this project:
Collected as much documentation as I could find. I could use some help completing this.
I have ordered/received all the parts based on the BOM I have.
Look forward to getting your input and help as this build progresses.
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I'll be willing to bet sluckey will help on all fronts, since he's a moderator here and the most helpful person I think I've met :)
I've built the same amp, but did the 30 watt version (ac 30/4) and love it, so I also know a bit about the amp.
Not sure if you've found this link but there's a long forum thread on the build here:
https://el34world.com/Forum/index.php?topic=17184.0
You can order the turret board for it from doug here on the site (see the link in the above forum thread).
I think you'll love it, the tremolo is really cool, and I love the gain of the EF86 on this thing.
Please post build pictures for us, we love em.
~Phil
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Hi Skip. Welcome to the forum. Glad you're interested in the AC-15. I'll be following your progress with interest.
I have found some discrepancies between the documentation (slight design differences, Mod's, BOM lists, etc..) so my first goal is to have a complete set of design documentation and vet it here on the forum before building. I am hoping some of you can help me fill in the gaps of my documentation.
Yeah, there were several discrepancies. Several people have built this project using my docs and I thought we had ironed it out pretty good, but always some more gremlins hiding. It seems the more you try to produce accurate docs the more hiding nooks you create for the gremlins. So, let's get those cleared up so you can have a successful project. Start listing particular errors you have found and we'll tackle them one by one. I'll make corrections as needed and then I'll make the revised Visio drawings available to you.
Meanwhile I'll give you something to start thinking about. I don't have a chassis layout for this amp. But, the main thing is to use a 20" wide chassis. My board layout is drawn full scale. So are the tubes and control panel. You will need to treat the board, control panel and tube lineup as one unit. IOW, don't deviate from this part of the layout. I spent a lot of time getting the front panel, board, and tube lineup to work together with a neat and quiet layout. My board and tube lineup will not work well with the original AC15 front panel. You would have a rats nest of wires. I can give you more specifics and you will also be able to see all the dimensions and how they are related when you get the actual Visio file. All other components (mainly power supply stuff) were fitted after the board, tubes and front panel holes were drilled. And I included a lot of pics that should give you some good ideas about how to put it all together, including the power supply. Keep in mind, you will have to work from the schematic to wire the power supply.
So, let's get started. There are several others that will likely join in also. One guy has built quite a few of these so he probably has a lot to bring to the table. Just take your time, measure twice, cut once, and ask questions. And by all means, lets fix the discrepancies in the docs.
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I have now built 7 of these thing. 15 Watters with an EF86 (which now I add switching values for Vox and Matchless). Doug has the board, but I like making it. Loads of turrent to stake.
The Chassis I use is 19" x 8" x 2.5. This build documentation must work as I have never had to troubleshoot a single one. Fires right up. I added a Fender Reverb to one. Waste of time IMO. Effects loop, sure. The amp will quickly move into overdrive, but not noticeable unless Reverb is heavy and then it gets real loose. I tried additional filtration, but it loses the true old Vox feel.
I had an original when younger and it simply overheated and ate tubes. I run voltages lower than Sluckey and it makes a difference. Simply a bit lazy and spongy. I am closer to 300VDC on the plates. Almost exactly as the Schematic. The tone is the same with about 350 Plate volts and does have noticeably more headroom, but I have a 18 Watt EL84 that punches a lot, I wanted more sag with this one.
I built a head version and a single 12 cab and used a Celestion Blue. Sounds perfect, but I no longer use 2 inputs. One combine both and volumes work to mix the 12AX7 Tremolo with the EF86 preamp. Go ahead and plan the slowing of the tremolo, the original design doesn't get slow enough for me. YMMV!
Welcome and have fun. Great Re-design!
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Progress:
Since my last post I have been busy creating my own set of documentation using Visio (my design tool of choice). Thanks to Sluckey for his collection of Visio Shapes my design documents look better than ever.
While creating my own documentation is tedious and time consuming, it does allow me to get a much better understanding of the design and also allows me to make any changes that I may incorporate in the build.
Circuit board drilling and jumper templates
The first docs I tackled was the circuit board drilling and jumper templates. Even though I bought the completed board with turrets from the Hoffman Amp site, I still need to drill the mounting and wire pass-thru holes. I made a full size photo copy of the Hoffman board and imported it into Visio. I also imported the image of Sluckey's board template and superimposed the two on top of each other. I then placed turret, mounting and wire pass-thru hole shapes in the proper places. You can easily copy/invert the diagram for a the bottom side of the template. I then made the jumper templates using the templates.
ZZ-AC15 Circuit Board Component Layout
I then inverted/super-imposed the top and bottom jumper templates onto each other for the component layout diagram. Again, using Sluckey's Visio shapes and original design document, I recreated the complete component layout.
ZZ-AC15 Chassis Layout
I then used the completed component layout diagram as the start of the Chassis Layout. Using the original design document, I recreated the Chassis Layout.
<See Attachment ZZ-AC15 Chassis Layout>
ZZ-AC15 Ground Scheme
Using the original design document, I recreated the Ground Scheme.
ZZ-AC15 Power Section Chassis Layout
This design has a few features/components that I have not built before. These include a standby switch and EZ81 Rectifier tube. So creating a power section chassis layout was important for me to understand how to wire this section correctly. As there is no prior design, I relied on the existing schematics available. The original AC15 schematic has no standby switch. Sluckey's annotated (original) AC15 schematic has a standby switch located after the Choke, and Sluckey's Detailed AC15 schematics has the standby switch located before the Choke.
Here are the two versions:
<See Attachment ZZ-AC15 Power Section Chassis Layout V1>
<See Attachment ZZ-AC15 Power Section Chassis Layout V2>
Questions:
- Are both designs for the location of the standby switch correct? Is one better than the other? Is one preferred over the other? Look forward to hearing your replies on this.
Next Steps:
My next step is to create a Parts List and inventory what I have on hand.
Happy Building :-)
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You have been very busy! Nice work! Making these drawings is an excellent way to get intimate with this amp.
Sluckey's annotated (original) AC15 schematic has a standby switch located after the Choke...
I never annotated the original schematic. You must be looking at someone else's work?
...and Sluckey's Detailed AC15 schematics has the standby switch located before the Choke.
Here are the two versions:
<See Attachment ZZ-AC15 Power Section Chassis Layout V1>
<See Attachment ZZ-AC15 Power Section Chassis Layout V2>
I've never seen these two drawings. I assume these are your work? I put the standby switch between the rectifier tube and the choke as seen on my main schematic or in the mod pdf. I never put it after the choke, although it should work fine there as well.
I'd like to suggest a simple change to your power section chassis layout... Connect the IEC Line terminal to the end lug of the fuseholder. This is a safety feature.
And just FYI, I used a 120v neon indicator lamp rather than a 6.3V lamp. That was just my preference. I think most guys have used a 6.3 lamp.
I never heard back from you about the discrepancies in the docs. I guess you were able to resolve these?
Here's a tip about the way I work with Visio. May be useful to you. My board layout has multiple layers. Components on one layer, turrets on another layer, jumpers on another layer, wires on another layer, etc. Doing things this way make it very easy to create the drill guide, and jumper guide. For example, to make a drill guide, just turn off the layers you don't want to see on the board layout, Copy the visible stuff, and paste into a new sheet. Wala, you have a drill guide. Works the same for the jumper guide. This way there are no differences between the sheets.
Looking forward to your next steps. Will you drill and stake your own boards or just buy Hoffman's board?
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Thanks for the quick rely.
Quote
Sluckey's annotated (original) AC15 schematic has a standby switch located after the Choke...
I never annotated the original schematic. You must be looking at someone else's work?
See the attachment for the doc I was referring to.
The two power section drawings were mine. I do them to make sure I get any unusual wiring right during the build.
I have updated them per your comments on switch location and safety wiring. thx!!!
I never heard back from you about the discrepancies in the docs. I guess you were able to resolve these?
I'll send you a PM with my notes from my review. I pretty much have resolved all my questions from this though.
Thanks for the tips on layers. I have never used the layer feature before, bit I can see how it would be helpful.
Looking forward to your next steps. Will you drill and stake your own boards or just buy Hoffman's board?
I did buy the Hoffman board, but I still need to drill the wire pass-thu and mounting holes as they no longer drill these. They only drill/mount the turrets. So I needed an updated template as thier board is a little different than your original.
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See the attachment for the doc I was referring to.
I don't recall ever doing that. Doesn't necessarily mean that I didn't. :icon_biggrin:
I'll send you a PM with my notes from my review.
OK, thanks.
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Output Transformer Wiring:
I noticed that the Output Transformer (Hammond 1650F - see attachment) has more Primary wires than I am used to in my Fender builds. Typically the OT's I have used have only the red (B+), blue (plate) and brown (plate) wires. This transformer has an additional two wires (Green/Yellow, Black/Yellow) indicating these should be connected to the Screen Grid. Also, the secondary wiring is different than the OT's I have used in the past. Usually there is a ground, and one wire for 4ohm, 8ohm and 6 ohm. This OT has a different wiring scheme defined for each output resistance.
Also, the Grounding Scheme diagram (attached) shows OT Secondary Grounds (Black and Black/Yellow) going to the Chassis Ground.
Here is what I know (or think I know) and do not know in terms of wiring:
Primary's:
Blue - V7 EL84 pin 7
Blue/Yellow - ?????
Red - Circuit Board "A" connection
Brown/Yellow - ?????/Yellow
Brown - V8 EL84 pin 7
Secondary's (I am wiring for 8 ohm speaker output):
Yellow - Output Jack Tip
Green/Yellow - connected to Green
Black Yellow - connected to Black
Green - connected to Green
Black - Output Jack Ground
Can anybody help me get this right?
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The blue/yellow and brown/yellow wires are screen taps and are not used in this amp. Securely tape up the separate ends and tuck out of the way. DON'T CONNECT THEM TOGETHER! These wires have B+ on them.
As for the secondaries
If you only want a single 8Ω speaker jack... Solder the green and green/yellow wires together, tape the ends, and tuck out of the way. Connect the black and black/yellow wires together and solder to the ground lug on the speaker jack. Solder the yellow wire to the tip lug of the speaker jack. That's all if using a switchcraft style jack. If you are using a Cliff style jack that has an isolated sleeve (ground) lug, then connect an additional wire from the jack sleeve lug to your chassis power ground.
Now, if you choose to have a 4Ω jack as well as a 8Ω jack, just study the big pic of the guts on my website. I bet it will make sense.
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Thanks Sluckey, that is the information I needed. That completes my design documentation.
I have drilled out the wire pass-thru and mounting holes in my Hoffman Turret board and am now working on installing the above and below board jumpers.
Stay Tuned...
.
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I am including the 6-position 2-pole Presence switch in this build (see attached picture below) with the following settings (per Sluckey's mod notes):
1- n/a
2- .0047uf
3- .0022uf
4- .0015uf
5- 500pf
6- 220pf
I understand how the switch works and get wired. My question is what is the best way to physically mount the components on the switch? Seems like it could get very crowded. Does anyone have pictures of this switch wired up?
Your help is appreciated!!!!
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Look here. Blow it up big so you can clearly see all the jumpers on the switch...
http://sluckeyamps.com/VAC15/Vox_AC15_mods.pdf
Or, you may prefer this style on my Dual British Lite. It's basically the same except one additional cap and they are physically laid out differently (cleaner I think). Here's a pic...
http://sluckeyamps.com/dual_lite/big_guts.jpg
And here's the layout. Blow it up big so you can clearly see all the jumpers on the switch...
http://sluckeyamps.com/dual_lite/dual_lite.pdf
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Excellent project! I've been wanting to build one for a quite some time now. I'll be following your build and am eager to reading your comments on how it plays and feels!
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This is my next build. I am going to use a pro jr, for the iron and chassis and cab. No tremelo
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I'm salivating following this thread. I've been looking for a donor amp. Maybe my Peavey 110 will be the guinea pig. Or maybe I'll make a new cabinet. Decisions, decisions.
:icon_biggrin:
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If anyone's interested, here's the build i did of the same amp, but as an AC30/4, they're identical amps except the 30 watter uses 4x el84 output tubes instead of two:
That's the playlist, there are a ton of videos showing the build process over time.
~Phil
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Just wanted to mention, I used a 12 position switch for brilliance for mine, but removed the cap from the board. 12 different caps are quite a lot, but this allows me to deepen the tone as well as cut bass and adds flexibility since I use a Wet/Dry setup. The AC-15 is my main signal without any modulation except I do use the Tremolo/Vibrato some on the AC-15. Closed back or just slightly open back to me sounds better with the Celestion Blue. Expensive, yes. You could get a copy like a Blue Dog or a Warehouse Black and Blue, but they are not that close so if a Chiming Vox with a Blue is what you want, spend the money.
I mentioned I don't build them with 2 inputs anymore, just switching for one or both channels. There is an advantage to having 2 inputs and being able to mix the 12Ax7 and EF86 and mixing them. A high gain pentode in the preamp sometimes clashes with distortion and even overdrive pedals, So I use the normal input and mix in the EF86. This is not often, but can be a problem if you like Fuzz. You seem to have the experience to determine you preferred tone, just sharing some of the things I have learned from building a few.
This one in the photo is the amp I use along with a 2, 10 Princeton Build. The 10's help a lot with taming modulation effects. This is the reason I wanted to be able to pass a bit more lows with the AC-15. Together the clean tone with Tremolo running on both amps is amazing. Hit the AC-15 with a little boost and you will start making 80's shredder faces.
Also, Everyone seems to reach for the screened EF86, but the NOS TESLA EF86 with the dark and usually crappy looking plates are a tad more raw sounding. EL84's vary a lot too and new production will hold up easily to voltages, but Pan Getter RCA have less fizz and are affordable. If you can swing it, plug in a pair of NOS Amperex. The have a extremely fluid transition into clipping and very early sustain without much breakup and continue this to full outright overdriven tone ALL which can be controlled mainly with pick dynamics.
This is a true vintage sounding Vox.
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Here is my current status on the project:
Design Phase:
Grounding Scheme - I have decided to go with an Isolated Grounding Scheme. This has proved very effective on my previous builds in reducing unwanted noise. My goal is to isolate the Pre-amp grounding from the Power Amp grounding.
In order to do this I isolate the grounds for the input jacks, control panel components and the circuit board low power grounds from the chassis. These grounds are run to terminal strips that are also isolated from the chassis. Isolating the control panel pots and switches from the chassis is not necessary as these are already isolated from the component bodies.
For the input jacks I use Cliff Jacks, the jacks bushing is plastic so the ground is isolated from the chassis.
The terminal strips must be isolated by using plastic nuts, bolts and washers.
Chassis Blueprint - I decided to go with a 20" x 8" x 3" chassis. I like the extra room the 8" depth and 3" height give me. I ordered a custom built chassis and engraved face plates from Synaptic Amp (www.reverb.com/shop/SYNAPTICAMPS). Steve at Synaptic Amps is awesome to work with and worked very hard to get my face plate design perfect.
Pre-Assembly Phase:
I always look for the list of things that need to/can be done ahead of the main build. See attachment for Pre-Assembly tasks and pictures. I still am waiting for the face plates so I have not drilled the front/back of the chassis yet.
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Great videos and great build Skip. That should be one helluva an amp when you're done.
Cheers!
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I have been busy since my last post.
After the preassembly work was completed, I of course found a few more minor preassembly tasks I had forgotten along the way.
Complete Chassis Drilling:
I received my face plates which allowed me to drill the rest of the component holes.
Test Assembly:
Next I did a test fit of all the components into the chassis. This helped me make sure all the components fit properly, make any adjustments required as well as determine the best order in which to do the assembly as I proceeded through the build.
Circuit Board Assembly:
Now it was time to work on the circuit board assembly. I learned a great deal during this task as this was my first turret board (all my past circuit boards have been using fiberboard and grommets). I placed/checked/double checked/soldered all the components on the board working from right to left, carefully trimming the excess wire from beneath the board. Then I worked the interconnection wires from the back of the board (front chassis side) clockwise around the board leaving plenty of extra wire to work with later.
Filament Wiring:
Working from left to right I cut and test placed the filament wiring for each of the tube sockets. I was careful to pay attention to doing proper phase wiring using green and black wiring to distinguish between the two wires. I also kept the twisted wire pairs tight against the chassis.
Power Section Wiring:
This was the most challenging work to date as I was determined to make my wire routing look as good as Sluckey's. I tried to create a plan on paper (in Visio actually) but found it too much of a task so I started wiring the power section component by component and determining the best routing as I went. When I was done I came back and used zip ties to hold the wire bundles in place. In the end I was pretty happy with the overall result.
See my attached PDF for a summary and pictures.
Next I am working on installing my grounding system.
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Lot of progress. That really looks sharp!
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It was a busy weekend and I made it to the final stage of the build.
I installed the grounding system. Both the isolated front controls ground and the power section chassis ground.
Next I prepped the shielded input connection wires and installed them from the input jacks to the isolated input standoffs. Then I installed the input 33k screen grid resistors from the isolated input standoffs to V2/V2.
Th volume knobs were next to install.
Now I wired the remaining output transformer wires to the output jack and power tubes.
And finally the biggest task of all, installing the circuit board and connecting all those wires. Working left to right, I simply soldered each wire to the front panel controls and ground connections. Then I worked left to right soldering each wire to the back panel and tube socket connections. This went pretty quickly and easily. I checked my work as I went along regularly.
See my attached PDF for a summary and pictures.
My next step is to recheck all my work against my design documentation (once again) and make any required fixes.
Then I will perform the first power up and testing and debugging.
Stay Tuned
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Whoa that looks great! I'm excited to hear tone samples!
~Phil
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That amp looks familiar. So does that amp cradle! :icon_biggrin:
Not just done, well done!
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That amp looks familiar. So does that amp cradle!
Forgot to mention that I had found the amp cradle DIY on your site a while back and built one. Works great!!!!! Thanks!!!!
So I completed my review and first round of tests.
The Good News:
No smoke, sparks or funny smells
Makes really loud good sounding tone
Really happy with the volume and tone so far!!!!!
The Bad News:
There are a few issues I need to resolve
There are really two issues that are most apparent.
1) Hum Issue: When the amp is powered up and operating with the Tone (Top Cut), Normal and Vibrato Volume controls all dialed all the way down, the amp produces a loud annoying hum.
a. When the Tone, Normal or Vibrato Volume controls are dialed up to about 2.5, the hum goes away.
b. The volume controls both only behave normally from 2.5 up.
2) The Vibrato Channel has a few issues beyond issue #1.
a. The overall volume is less than the normal channel
b. The Vibrator/Tremolo Effects do not function at all.
See my attached PDF for details of the testing procedure.
Both of these issues have me initially stumped as to where to start working to a resolution. I have not experienced these specific issue on past builds. Also, this is the first amp I have built with any on-board effects.
Any suggestions would be much appreciated.
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The Vibrator/Tremolo Effects do not function at all.
did you have FS plugged in? (don't ask how I know:)
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I think the hum and strange behavior of the volume pots may be related and possibly caused by a ground issue.
The vibrato channel is lower volume than the normal channel. Just the way it is. The brilliance switch does not affect the VIB channel. The top cut does affect both channels.
The footswitch must provide a ground to ***ENABLE*** the trem/vib oscillator. If you look closely at my big guts pic you will see that I used a Switchcraft 12A switching jack and its wired to ground the tip when nothing is plugged in. Maybe I'll revise my schematic and layout to make that more obvious. The schematic shows this but if you are not familiar with trem circuits it's easy to overlook.
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Just to note that best practice is to connect the CT of the HT winding to the reservoir cap's negative terminal (rather than to a common 0V point shown in the layout), as that will mitigate for ripple current contaminating the 0V circuit.
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The grounding scheme he used works very well.
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The footswitch must provide a ground to ***ENABLE*** the trem/vib oscillator. If you look closely at my big guts pic you will see that I used a Switchcraft 12A switching jack and its wired to ground the tip when nothing is plugged in. Maybe I'll revise my schematic and layout to make that more obvious. The schematic shows this but if you are not familiar with trem circuits it's easy to overlook.
I replaced the footswitch jack with a switching jack and jumped the ground and shunt terminals. That did the trick. The effects are now working.
I do not know exactly what to expect from these effects as I never played through a Vox Acxx before. But For both Tremolo and Vibrato I have the Speed control effective from 8 o'clock on up and the Depth control seems only effective from 2 o'clock on up. And at full speed the effect is not very noticeable. Does this seem right?
I think the hum and strange behavior of the volume pots may be related and possibly caused by a ground issue.
I am starting to work this issue. I agree that it seems grounding related which is where I will start my investigation.
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In trem mode the effect should simply vary the guitar signal amplitude (volume). In vib mode you should also hear a noticeable pitch (frequency) shift.
You can replace the oscillator cathode R/C with a red or yellow LED for a stronger oscillator signal. The LED should also give a more constant oscillator signal amplitude across the speed range.
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Almost Done
Note: Other than the issue below, the amp seems to be working wonderfully. The tone and volume is great, the effects are working fine (although I may tweak them a bit later to get more pronounced depth) and overall I am quite happy with the build. I have learned a many great new techniques I plan to apply to my future builds (I keep thinking about building another Fender Champ , hot rodded to the extreme, with a turret circuit board, selective tone biasing, neatly bundled PT/OT wires and custom face plates).
Regarding the strange Volume and Tone pot behavior WRT the HUM:
I have been checking that the grounding system is installed properly and is working as expected.
See attached Ground Scheme PDF.
I verified that the power section part of the grounding system is installed correctly and all the ground points have continuity.
I verified that the isolated part of the grounding system is installed correctly and is indeed isolated by disconnecting its one point of connection to the Chassis (Orange wire between the chassis grounds and the isolated grounds on diagram).
Interesting Revelation but not the obvious solution:
I also worked around the inside of the chassis checking for any unintentional grounds (i.e. ground shorts). I came across two suspicious ground hits. These were turrets on the board, one connected to the Normal Volume center pot pin (green wire) and the other connected to the Vibrato Volume center pot pin (blue wire).
After some investigation I discovered that when the volume pot is turned all the way down, the resistance between the left and center pins is almost zero (of course) and this allows the ground to travel back down the green and blue wires to the circuit board connection. I never realized that a pot behaves this way but I checked it against several other pots in my drawer as well as in one of my Princetons.
When the pot is turned up a bit (like to 2.5) and the resistance goes up a bit (to something like 35k ohms) this behavior stops. It turns out that this is exactly when the HUM stops. So the pots also exhibit a level of "slop" between zero and 2.5. The resistance does not steadily rise to 35 from zero, but rather JUMPS from zero to 35.
So in some way I believe that the strange Volume and Tone pot behavior and HUM is related to this pot behavior. BUT, I have never seen this problem before and have no clue how to explain it.
Any other ideas from you all would be appreciated.
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Are you using audio taper volume pots?
I don't like that ground scheme! I suggest you remove that orange wire that ties your preamp/control panel grounds to the power ground. The control panel grounds (I used a buss) and the NOR and VIB board grounds should all tie together to a chassis ground lug that is mounted very near the input jacks. The chassis will provide the return connection to the PT red/yel center tap.
The board PA and PI grounds, OT sec. ground(s), speaker jack ground, and cap can ground should all tie to the same chassis ground lug as the PT red/yel center tap. These power grounds should not rely on the chassis for current flow back to the PT red/yel center tap. This power ground lug should be physically located near the PT and cap can. You can eliminate one of those terminal lug strips.
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if you haven't sourced the 1650F OT, then consider the 1650FA - it's a replacement for the 1650F.
the 1650FA has the secondaries internally connected to provide single wire 4-8-16Ω taps and a common.
https://www.arrow.com/en/products/1650fa/hammond-manufacturing?gclid=CjwKCAjwycfkBRAFEiwAnLX5ITTD-LkCIrOIIZt5R9B41-Nipw1j5x611V2km8eLcf0_WEFm41IOlxoCIiUQAvD_BwE
free shipping if you're in the Continental US!
--pete
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if you haven't sourced the 1650F OT, then consider the 1650FA - it's a replacement for the 1650F.
Way beyond sourcing, but thanks!!!!
Are you using audio taper volume pots?
Yes. 500k Audio Tapered.
So I reworked the grounding scheme in the manner you described.
Power Section Grounding all to one chassis ground at one of the PT mounting bolts.
Control Section Grounding untied from the power section and bolted to a new chassis ground directly under the input jacks.
No change in the Volume/Tone/Hum behavior though :BangHead:
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The normal and vibrato preamps have absolutely nothing in common. The fact that they both exhibit the same behavior with the volume pots strongly suggest a less than perfect ground to the pots, maybe even only one gremlin affecting both pots or identical twin gremlins affecting each pot. It's time to share some high rez gut pics, especially clearly showing the ground connection on each pot and how the pot ground lugs are connected to a dedicated preamp ground. The pics in your pdf files are nice for casual viewing but they are very lacking in the kind of detail we need to help troubleshoot your problem. The pics will likely be too big to post directly on the forum so upload your hi-rez pics to the net and just post a link to them.
Meanwhile, try this. Divide and conquer. Pull V1 and V4 to totally disable the VIB channel. Just leave them unplugged until we fix the NOR channel hum. We're gonna work with the NOR channel only. With the NOR VOL pots turned to zero, use a gator clip lead to connect the center pot lug to chassis. Does that kill the hum?
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Result:
Pulled V1 and V4.
Turned Nor Vol, Vib Vol, Tone to 0.
Attached gator clip to center lug of Nor Vol to chassis ground.
Hum still present, but slightly lower volume with than without. But when the Nor Vol, Vib Vol or Tone turned up to 2.5 the amp is totally quiet.
Pictures:
Wide Shot: https://www.flickr.com/photos/23805934@N02/46519428325/in/album-72157626245738182/
Vol Pots: https://www.flickr.com/photos/23805934@N02/46519430345/in/album-72157626245738182/
Control Panel Chassis Ground: https://www.flickr.com/photos/23805934@N02/46519428525/in/album-72157626245738182/
Tone Pot: https://www.flickr.com/photos/23805934@N02/46519429505/in/album-72157626245738182/
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One other interesting note:
If I attach a gator clip to left or center lug of Nor Vol and simply hold the other end of the gator clip, the amp goes quiet.
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It appears that you are using nylon screws to attach those two 5-lug terminal strips to chassis. Why?
I only see one wire connected to your added preamp ground lug. Where is the other end of that black wire connected?
I would replace those nylon screws with steel screws. Then run a short wire from each of those terminal screws to that added ground lug.
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One other interesting note:
If I attach a gator clip to left or center lug of Nor Vol and simply hold the other end of the gator clip, the amp goes quiet.
If you connect the gator clip to chassis and hold the other gator clip, does the amp go quiet? Do you have any fluorescent lights near the amp?
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It appears that you are using nylon screws to attach those two 5-lug terminal strips to chassis. Why?
That was part of my isolated grounding scheme. Nylon bolts isolate the terminal strips from the chassis. The idea is to control the low level control panel signal grounds and keep them from getting mixed in with the higher power level grounds in the chassis. That is the theory anyways. Here is a link to the article that I got the idea for this grounding scheme. http://www.aikenamps.com/index.php/grounding (http://www.aikenamps.com/index.php/grounding)
I only see one wire connected to your added preamp ground lug. Where is the other end of that black wire connected?
See attached diagram for the grounding scheme. There are 2 terminal strips (1-5 lug, 1-7 lug) for the control panel grounds, the 7 lug is tied to the 5 lug with a wire, and the 5 lug is grounded to the chassis.
I would replace those nylon screws with steel screws. Then run a short wire from each of those terminal screws to that added ground lug.
I Am going to re-work the entire control panel grounding and take all the grounds to the single chassis grounding point under the input jacks.
If you connect the gator clip to chassis and hold the other gator clip, does the amp go quiet? Do you have any fluorescent lights near the amp?
No, connecting the gator clip to the chassis and holding the other end of the gator clip has no change in the hum. There is a fluorecent light nearby, but removing the light does not change the hum.
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If I attach a gator clip to left or center lug of Nor Vol and simply hold the other end of the gator clip, the amp goes quiet.
This still suggest the ground connection to the NOR vol is not quite right. Although your isolated terminal strip ground should be OK. Maybe redoing the control panel groung will fix it.
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I reworked the control panel grounding. I removed the isolated terminal strips and chassis ground. I replaced them with chassis grounded 3 lug and 5 lug terminal strips. See attached diagram.
This has not resolved the hum issue. The only thing I have been able to do to make the issue go away is connect a gator clip to the left terminal of the Vib or Nor Volume pot, and set the other end, un-connected, on the work bench. Then the hum stops. Not permanent solution.
Any new ideas would be appreciated.
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That grouns system should work fine. Maybe this hum is not caused by poor grounds. The gator clip on the volume pot ground lug is a puzzle. Do you have a metal bottom plate for the chassis? If so bolt it on. If not, rool out a length of aluminum foil on the bench top. Set the amp on the foil, open side in contact with the foil. Hum any better?
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Do you have a metal bottom plate for the chassis? If so bolt it on. If not, rool out a length of aluminum foil on the bench top. Set the amp on the foil, open side in contact with the foil. Hum any better?
No bottom plate.
Rolled out the aluminum foil and set the amp open side on the foil. No change. :dontknow:
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On the normal volume pot that leads to your 6 position switch, try from the layout you posted remove a and b from switch and exclude for testing. IOW eliminate the switch. I understand the normal channel preamp is supposed to be separate and if the vibrato channel does the same common thinking says one cannot cause the other to hum.
I assure you both of my preamps change tone when switched. Does your power trans have a CT for heaters or resistors for a ct? Try lifting and using resistors. If already using artificial ct, check the resistor values to insure they are the same.
Try running a seperate earth ground and connect the gator clip your quiet hand to this. Eliminate you and the chassis.
Have you tapped on your tubes while the hum is present? Does it change? Got another set of El84 known to be good?
Just thinking out loud.
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On the normal volume pot that leads to your 6 position switch, try from the layout you posted remove a and b from switch and exclude for testing. IOW eliminate the switch.
I did that along with pulling the Vib channel tubes so I was just dealing with the Normal channel. No change.
I assure you both of my preamps change tone when switched. Does your power trans have a CT for heaters or resistors for a ct? Try lifting and using resistors. If already using artificial ct, check the resistor values to insure they are the same.
I have CT for the heaters. I will try installing an artificial CT and lift the PT CT and see what happens.
Try running a separate earth ground and connect the gator clip your quiet hand to this. Eliminate you and the chassis.
Tried this, no change.
Have you tapped on your tubes while the hum is present? Does it change? Got another set of El84 known to be good?
Tapping does not change anything. I actually have another 2 sets (That I had replaced in my Mesa Boogie 20/20 stereo amp) of EL84's. I tried both sets with the same results.
Appreciate the ideas...
.
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Just how much of a hum is this? Is it loud enough to be heard while you are playing at bedroom levels? Do you have to raise your voice to be heard above the hum? Is it low enough that you have to listen closely to hear it? Is it 60HZ or 120Hz? Or neither?
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Just how much of a hum is this?
Enough to be annoying.
Is it loud enough to be heard while you are playing at bedroom levels?
It goes away as soon as i turn the tone, nor vol or vib vol up past 2.5. This hum is transient and is constant until it goes away when the tone, nor vol or vib vol are turned up past 2.5.
Do you have to raise your voice to be heard above the hum?
No
Is it low enough that you have to listen closely to hear it?
No
Is it 60HZ or 120Hz? Or neither?
Not do not know how to tell the difference.
I am close to just moving on and keeping the tone knob at 3 or higher. In this state the amp works fine and is quiet. The volume is way above my expectations, the tone is great, the on board effects sound good. Then maybe one day I will have an epiphany that will help me solve this WEIRD problem.
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Some DMMs can measure frequency. If yours can, then connect the meter to the speaker and get the amp to hum. Set the meter to measure ac volts. You should have a reading in the display that represents the amplitude of the hum. Now set the meter to read frequency (Hz).
You may want to build confidence in checking frequency by checking the filament voltage and switching to Hz mode. Should be a solid 60Hz.
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Some DMMs can measure frequency. If yours can, then connect the meter to the speaker and get the amp to hum. Set the meter to measure ac volts. You should have a reading in the display that represents the amplitude of the hum. Now set the meter to read frequency (Hz).
You may want to build confidence in checking frequency by checking the filament voltage and switching to Hz mode. Should be a solid 60Hz.
My meter does measure Hz. I recorded a frequency of ~120Hz when the amp produces the hum.
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120hz is post rectifier hum, so PS, rather than filaments, unless filaments a rectified DC
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120Hz originates in the power supply. Doesn't necessarily mean that your problem is in the power supply though. Could still be a grounding issue.
Divide and conquer time... Pull V1, V2, V4, and V6. This leaves only the PI, power amp, and rectifier tubes plugged in. Do you still have the hum issue?
Next you will need a couple gator clip test leads and a filter cap to use as a test cap. 20΅F at 450v is fine. Other values between 10 and 50΅F are OK too, just be sure the voltage rating is sufficient for this amp. We will be bridging this test cap across each of the filter caps in the amp.Connect the negative lead of the test cap to chassis. Use the other clip lead to connect the positive cap lead to one of the cap terminals in the can and notice if the hum goes away. Now move to the other cap in the can and repeat. Next connect the test cap to each of the caps on the board. Did any of these tests kill or significantly decrease the hum? If so, replace that cap.
Report your findings.
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120Hz originates in the power supply. Doesn't necessarily mean that your problem is in the power supply though. Could still be a grounding issue.
Divide and conquer time... Pull V1, V2, V4, and V6. This leaves only the PI, power amp, and rectifier tubes plugged in. Do you still have the hum issue?
There is still some hum, but different. But other weird noises are now present as follows:
All knobs at 0: Slight hum, less than original hum.
Tone knob at 3: Slight hum, a little different than the above.
Tone knob at 3, Nor Vol knob at 3: All quiet.
Tone knob at 0, Nor Vol knob at 3: Really loud squeal.
Tone knob at 3, Vib Vol knob at 3: Louder hum.
I will now work the other suggested tests.
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Next you will need a couple gator clip test leads and a filter cap to use as a test cap. 20΅F at 450v is fine. Other values between 10 and 50΅F are OK too, just be sure the voltage rating is sufficient for this amp. We will be bridging this test cap across each of the filter caps in the amp.Connect the negative lead of the test cap to chassis. Use the other clip lead to connect the positive cap lead to one of the cap terminals in the can and notice if the hum goes away. Now move to the other cap in the can and repeat. Next connect the test cap to each of the caps on the board. Did any of these tests kill or significantly decrease the hum? If so, replace that cap.
Do I replace V1, V2, V4 and V6 for these tests?
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Next you will need a couple gator clip test leads and a filter cap to use as a test cap. 20΅F at 450v is fine. Other values between 10 and 50΅F are OK too, just be sure the voltage rating is sufficient for this amp. We will be bridging this test cap across each of the filter caps in the amp.Connect the negative lead of the test cap to chassis. Use the other clip lead to connect the positive cap lead to one of the cap terminals in the can and notice if the hum goes away. Now move to the other cap in the can and repeat. Next connect the test cap to each of the caps on the board. Did any of these tests kill or significantly decrease the hum? If so, replace that cap.
Report your findings.
I just ran these tests with and without the V1, V2, V4 and V6 tubes. None of the tests eliminated or changed the hum.
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1. Locate the two wires that go to the top cut pot. Disconnect these wires from the board. Does it still hum? Leave the top cut pot disconnected while doing the next couple tests.
2. Disconnect the wire from the normal volume pot center lug at the board. Does it still hum? Leave this wire disconnected.
3. Disconnect the wire from the vibrato volume pot center lug at the board. Does it still hum? Leave this wire disconnected.
At this point you have no top cut, no normal channel, and no vib channel, and hopefully no hum. What's the report?
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1. Locate the two wires that go to the top cut pot. Disconnect these wires from the board. Does it still hum?
Note that the condition to create the hum is all knobs at zero.
When I disconnect either/both wires from the Top Cut Pot the hum goes away. The amp plays perectly (minus tone control).
If I connect the two disconnected Top Cut wires with a gator clip, there is no hum.
I replaced the Top Cut pot with a new one, the hum is back.
It seems that Top Cut knob is at least related to the underlying issue.
I did not leave the Top Cut DISconnected for the following tests as the hum was gone in that state.
Disconnected the Nor Vol pot. The hum was still present.
Disconnected the Vib Vol pot. The hum was still present.
Reconnected everything.
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Could you post a hi-rez pic that shows the top cut pot with wiring to the board? I want to see that entire left end of the board.
Then remove the knob and nut from the top cut pot and fold the pot back over the top of the board. Use a piece of cardboard to prevent the pot from shorting to anything on the board. Is the hum still present?
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Could you post a hi-rez pic that shows the top cut pot with wiring to the board? I want to see that entire left end of the board.
https://www.flickr.com/photos/23805934@N02/46792688424/in/album-72157626245738182/
https://www.flickr.com/photos/23805934@N02/46792688194/in/album-72157626245738182/
https://www.flickr.com/photos/23805934@N02/46792687814/in/album-72157626245738182/
https://www.flickr.com/photos/23805934@N02/46792687294/in/album-72157626245738182/
Then remove the knob and nut from the top cut pot and fold the pot back over the top of the board. Use a piece of cardboard to prevent the pot from shorting to anything on the board. Is the hum still present?
Still hum present.
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When I disconnect either/both wires from the Top Cut Pot the hum goes away. The amp plays perectly (minus tone control).
If I connect the two disconnected Top Cut wires with a gator clip, there is no hum.
So, you actually disconnected the two red wires at the pot rather than at the board? And then you used a gator clip to connect the two red wires together? And there's no hum?
This is crazy! Dead short and no hum. That's exactly what you have when you set the pot to zero (dead short), except you have hum.
Try this... With everything connected as normal, set the pot to zero. You should have hum. Now take your gator clip and short out the left and center pot terminals. Still hum?
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This is crazy! Dead short and no hum. That's exactly what you have when you set the pot to zero (dead short), except you have hum.
Try this... With everything connected as normal, set the pot to zero. You should have hum. Now take your gator clip and short out the left and center pot terminals. Still hum?
Yes, hum still present :w2:
I decided to re-run some tests and write down each step as follows:
All knobs to Zero
Hum Present
All knobs to Zero
Turn Tone up to 3
Hum gone
Amp operates properly
All knobs to Zero
Turn Nor Vol up to 3
Hum gets Louder
All knobs to Zero
Turn Vib Vol up to 3
Hum gone
Amp operates properly
All knobs to Zero
Disconnect left Nor Vol pot wire
Hum gone
Amp operates properly minus tone control
All knobs to Zero
Connect Disconnected left Nor Vol pot wire to left Nor Vol pot via gator clip
Hum Gone
Amp operates properly INCLUDING tone control
:dontknow:
All knobs to Zero
Completely Disconnected left Nor Vol pot wire from pot and board
Hum Gone
Amp operates properly minus tone control
All knobs to Zero
Connect left Nor Vol pot connection to board with gator clip
Hum Gone
Amp operates properly INCLUDING tone control
:BangHead:
All knobs to Zero
Install temporary new wire from left Nor Vol pot connection to board
Hum is Back!!!!!!!!!
:cussing:
I really do not understand this RELLY weird behavior.
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left Nor Vol pot wire
which view? are you talking signal or ground?
As bizarre as this is, have you wired the pot backwards swap outside wires :dontknow:
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Disconnect both green wires from the Brilliance rotary switch. Remove the rotary switch from the amp. Temporarily solder the free ends of the two green wires together. Got hum?
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Disconnect both green wires from the Brilliance rotary switch. Remove the rotary switch from the amp. Temporarily solder the free ends of the two green wires together. Got hum?
Hum still present.
BTY: In my previous post, the last 5 tests listed contained a cut/paste error. The Nor Vol referenced should have been Top Cut
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This is the test that boggles my mind more than any other:
All knobs to Zero
Disconnect left red Top Cut pot wire
Hum gone
Amp operates properly minus tone control
All knobs to Zero
Connect the Disconnected left red Top Cut pot wire to left Top Cut pot via gator clip
Hum Gone
Amp operates properly INCLUDING tone control
This makes no sence at all.
Has anyone seen anything like this before??? Where inserting an aligator clip into a connection changes the function of the amp.
Help appreciated as always.
In the mean time, I am starting some work on my next project. Tearing down my AA764 Champ (https://www.flickr.com/photos/23805934@N02/47529605471/in/dateposted-public/) and rebuilding it into a 5F1 Champ. I really never liked the AA764. It has ZERO character. While both my 5F1 Champ (https://www.flickr.com/photos/23805934@N02/47529605951/in/dateposted-public/) and 2x5F1 Stereo Champ (https://www.flickr.com/photos/23805934@N02/47476826082/in/dateposted-public/) are awesome. They scream character.
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This makes no sense at all.
:laugh:
to me, it's an "antenna" issue, the gator clip provides better blockage to stray noise than your wire.
try this. leave the wire connected then parallel the gator-clip with the wire.
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BTY: In my previous post, the last 5 tests listed contained a cut/paste error. The Nor Vol referenced should have been Top Cut
No harm done. Just a short detour down a dead end street. :icon_biggrin:
I'm wondering if that yellow OT wire is involved. It's very close to those magical red wires. Disconnect that yellow wire from the speaker jack, pull it out from under the board (hope you can get to that tape!), re-route around the end of the board keeping it away from the top cut wires, and reconnect to the speaker jack. I would plan to make this a permanent change. You'll likely have to lengthen that yellow wire.
Any change?
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This makes no sense at all.
try this. leave the wire connected then parallel the gator-clip with the wire.
Makes an even more annoying hum/squeal.
I agree with the "antenna" idea though. Here is more WEIRD behavior supporting this idea.
I connect the gator clip to the Tope Cut board side connection only, then set the other end on the work surface, and the hum goes away.
Put the unconnected side near my laptop, the hum returns.
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Another thought... Replace those two red wires. They look like low voltage control wiring (HVAC t-stat, or doorbell, or sprinkler system wires). That shouldn't be a problem for the top cut pot, but I think I also see some of that same wire used on the power tube screens. If it is in fact low voltage control wire I would replace it.
EDIT... Replace those red wires before you re-route the OT yellow wire. But rout the new top cut wires above the board, keeping them far away from any OT wires. Don't route them through those wire pass through holes on the board.
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Another thought... Replace those two red wires. They look like low voltage control wiring (HVAC t-stat, or doorbell, or sprinkler system wires). That shouldn't be a problem for the top cut pot, but I think I also see some of that same wire used on the power tube screens. If it is in fact low voltage control wire I would replace it.
I am using 22 ga Solid 300v wire for all the turret board connections. Is this wire not right for this application?
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Another thought... Replace those two red wires. They look like low voltage control wiring (HVAC t-stat, or doorbell, or sprinkler system wires). That shouldn't be a problem for the top cut pot, but I think I also see some of that same wire used on the power tube screens. If it is in fact low voltage control wire I would replace it.
I am using 22 ga Solid 300v wire for all the turret board connections. Is this wire not right for this application?
That wire is fine. I'm talking about LOW VOLTAGE CONTROL WIRE. 24VAC stuff.
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I know Sluckey and others here have built this amp with Slucky's layout and not had this problem, but since you are;
EDIT... Replace those red wires before you re-route the OT yellow wire. But rout the new top cut wires above the board, keeping them far away from any OT wires. Don't route them through those wire pass through holes on the board.
Yes, agree, but make them a tightly/evenly twisted pair when you do it. Very important that they are tightly and evenly twisted for it to work.
Those 2 wires are out of phase and twisting them will give some cancellation/protection to them. It might be enough to knock out the problem. I would have done it from the start. It's just good lead dress practice.
I'm wondering if that yellow OT wire is involved. It's very close to those magical red wires. Disconnect that yellow wire from the speaker jack, pull it out from under the board (hope you can get to that tape!), re-route around the end of the board keeping it away from the top cut wires, and reconnect to the speaker jack.
I'd try another tightly twisted pair here with the OT speaker jack wires. I'd have done this from the start, twist the OT secondary ground wire with the +speaker jack wire. Run them both together to the speaker jack and then, if your speaker jack is isolated from the chassis, run a single ground wire back to the power amp ground. Aiken is pretty strong on not having the OT ground current run through the chassis. So is Merlin and Kevin O'Connor.
Between moving those top cut wires away from the OT secondary wires AND twisting them tightly AND making the OT secondary wires a tightly twisted pair to the output speaker jack, that might knock out the problem. Probably have to do both. Unless, see below;
You did run a ground wire from the speaker jack back to the power amp ground, where you have the OT secondary common (ground) wire hooked up?
I don't see a ground wire going from the OT secondary to the speaker jack.
And since this amp has no -FB loop, I'd try moving the PI ground from the power amp ground to the preamp ground.
Again, I know this worked fine with no problems for Slucky and others the way Sluckey did his grounding, but you've got a bug-a-boo. :think1:
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Yes, I know he's using a much larger amp as an example but still,
From Aiken amps site;
What about the output jacks?
The current in the secondary winding of the output transformer can be very large. For example, in a 100W amp, the secondary current into a 16 ohm load is 2.5A. It is even higher into a 4 ohm load, at 5A. This means that you need to pay special attention to the grounding of the output jacks and the output transformer. It is important not to use the chassis for this return path.
The output transformer secondary has a common wire and one or more speaker taps, usually at 4, 8, and 16 ohms. The speaker taps usually go to an impedance selector switch, and then a single wire goes to the output jack tip connection. The common wire should never be connected to the chassis right at the output transformer. It should be run all the way to the output jack and connected to the sleeve connection of the jack. This accomplishes two things. First, it maintains the continuity of the connection in the event the output jack becomes loose. Second, it keeps the heavy secondary ground return currents from flowing in the chassis.
Note that there still must be a ground return path to the rest of the circuit if the amp uses global negative feedback. This should be in the form of a wire from the sleeve connection of the output jack to the preamp ground point where the phase inverter common connections are grounded, or to the ground of the portion of the circuit where the global feedback from the tip connection of the output jack is connected. Note that there will be no heavy currents in this wire. The speaker output jacks can be either isolated or non-isolated if you follow this plan, but it is usually best to isolate them to maintain control of the return current path for the global negative feedback, to insure it doesn't flow through a part of the chassis that may contain power supply ground currents.
Sometimes it helps to ground the common (sleeve) side of the output jack to the chassis even when no global negative feedback is used. Occasionally, an amplifier will have a high-pitched oscillation noise, or other type noise that will go away if you ground the output transformer common wire at the speaker jack sleeve terminal. In addition, there may be a potential for a small AC current to flow between the floating sleeve and chassis if the secondary is not grounded. This current is due to capacitive coupling in the output transformer, and may cause a mild shock if the speaker plug sleeve and chassis (or guitar strings) are touched while running a signal through the amplifier. Even though the potential for dangerous currents is low due to the galvanic isolation of the output transformer, the shock can still be annoying. For this reason, it is best to always ground the common side of the secondary even when no global feedback is used.
From Merlin's site;
The secondary side of the output transformer (if one is used) should always be wired directly to the speaker jack using heavy-gauge wire. This is true no matter what ground scheme is used. A separate wire (which does not need to be heavy gauge) should then run from the negative connection of the speaker jack back to an appropriate star. If global feedback is not used then this speaker ground wire should be returned to the power-amp star. If global feedback is used then the speaker ground should be returned to the local star of whichever stage the feedback happens to be applied to, which is usually the phase inverter.
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Hi,
New to your post but have been following silently a bit and maybe can help.
I agree with the "antenna" idea though. Here is more WEIRD behavior supporting this idea.
I connect the gator clip to the Tope Cut board side connection only, then set the other end on the work surface, and the hum goes away.
Put the unconnected side near my laptop, the hum returns.
But is it THE same hum. Does the hum from your laptop register the same 120Hz you got earlier with the pot connected? Even if it is the same frequency this could be a false positive. I think it would be unusual for shaft or any other part of your Top Cut pot to act like an antenna picking up outer noise, especially with the nob installed on the pot. And it seems unlikely the red wires inside the chassis would be picking up noise from anywhere outside the amp as well. It's a lot more likely they are picking up noise from inside the chassis somewhere. That yellow OT wire sluckey mentioned is suspicious. Also replacing the red wires and running them on top of the board as suggested can't hurt. Neither can putting a twist in them. Hopefully some combination of that advise from sluckey does the trick. Good luck!
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Didn't mean to infer outside noise, just any noise, and if I'm not mistaken R, C, and wire, make a pretty good dipole antenna (top cut circuit)
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Didn't mean to infer outside noise, just any noise, and if I'm not mistaken R, C, and wire, make a pretty good dipole antenna (top cut circuit)
Yes, anything after a coupling cap to the next stages grid will act like an antenna, that's why we often use shielded cable for grid wires.
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Another thought... Replace those two red wires. They look like low voltage control wiring (HVAC t-stat, or doorbell, or sprinkler system wires). That shouldn't be a problem for the top cut pot, but I think I also see some of that same wire used on the power tube screens. If it is in fact low voltage control wire I would replace it.
I am using 22 ga Solid 300v wire for all the turret board connections. Is this wire not right for this application?
That wire is fine. I'm talking about LOW VOLTAGE CONTROL WIRE. 24VAC stuff.
I never use that in any of my builds.
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EDIT... Replace those red wires before you re-route the OT yellow wire. But rout the new top cut wires above the board, keeping them far away from any OT wires. Don't route them through those wire pass through holes on the board.
Yes, agree, but make them a tightly/evenly twisted pair when you do it. Very important that they are tightly and evenly twisted for it to work.
You did run a ground wire from the speaker jack back to the power amp ground, where you have the OT secondary common (ground) wire hooked up?
I don't see a ground wire going from the OT secondary to the speaker jack.
And since this amp has no -FB loop, I'd try moving the PI ground from the power amp ground to the preamp ground.
Working on the new red Top Cut wires, above board and evenly twisted.
I do have a ground wire from the speaker jack back to the power amp ground, where the OT secondary common (ground) wire is hooked up?
I'll move the PI ground from the power amp ground to the preamp ground.
Tune back in tomorrow for an update..........................
Oh, and I really appreciate all the help. I am learning a great deal on not only techniques but debugging. And learning is one of the best things about this hobby. thanks everyone!!!!!!
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Because it's probably a problem area, I'd take the utmost care with those top cut wires.
A lot of guys twist wire pairs in a battery hand drill driver. They come out very tight and even.
I'd run the 2 wire ends towards each other 1st from each turret staying on/over the turret board, but away from that middle turret, so they are twisted together as soon as possible, with just a little slack in the 2 wire ends, not taught like a guitar string. Then with the 1st twist sitting on the board, straight up from the turret board, to keep them away from the OT wires. Then start to make a nice smooth arched curve towards the top cut pot, with the top of the arch level with the pots lugs. And the arch will give the wires a little room to move, flex, if they need it from the amp getting bumped when moving it.
More twists are better than less twists. Even though it's a short distance, 2 or 3 or 4 twists are not enough.
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I really don't believe the lead dress of those two wires is the issue. I rather believe this behavior is a crazy symptom of the real issue. Look at my wiring. I didn't do anything special with wiring the top cut...
http://sluckeyamps.com/VAC15/big_guts.jpg
I wonder if there is a gremlin living near that workbench. Have you tried the amp in another room? Or, even better, take it to another location. Same behavior?
I also am not convinced that your grounding scheme is not a factor.
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I really don't believe the lead dress of those two wires is the issue. I rather believe this behavior is a crazy symptom of the real issue. Look at my wiring. I didn't do anything special with wiring the top cut...
I did and I noticed that your OT leads come through under the rotary tone control. Skip's come through right under the top cut pot. And, like you noticed, is very close to 1 of the top cut pot leads, part of the power tube gird circuit. That OT wire has a lot of current going through it and is very close to a grid wire.
Plus, your OT wire then runs under the board on an angle that's different than Skip's.
He might still have to move the OT secondary around the end of the board like you suggested.
His lead dress at the EL84 tubes should get cleaned up too, some wires shortened, moved.
There's a grid wire laying along side that OT secondary wire that I don't trust.
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I also am not convinced that your grounding scheme is not a factor.
????
Skip's grounding scheme could be the problem?
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You guys are talking about my grounding scheme. Let me tell you where I am at on this:
My original design and implementation used an Isolated Grounding scheme as I described in an earlier thread:
"I have decided to go with an Isolated Grounding Scheme. This has proved very effective on my previous builds in reducing unwanted noise. My goal is to isolate the Pre-amp grounding from the Power Amp grounding.
In order to do this I isolate the grounds for the input jacks, control panel components and the circuit board low power grounds from the chassis. These grounds are run to terminal strips that are also isolated from the chassis. Isolating the control panel pots and switches from the chassis is not necessary as these are already isolated from the component bodies.
For the input jacks I use Cliff Jacks, the jacks bushing is plastic so the ground is isolated from the chassis.
The terminal strips must be isolated by using plastic nuts, bolts and washers."
See 1st attachment ZZ-AC15 Ground Scheme V1.0
After my build was completed and the "HUM" was discovered the debugging process started. At one point sluckey suggested I change my grounding scheme as follows:
"I don't like that ground scheme! I suggest you remove that orange wire that ties your preamp/control panel grounds to the power ground. The control panel grounds (I used a buss) and the NOR and VIB board grounds should all tie together to a chassis ground lug that is mounted very near the input jacks. The chassis will provide the return connection to the PT red/yel center tap.
The board PA and PI grounds, OT sec. ground(s), speaker jack ground, and cap can ground should all tie to the same chassis ground lug as the PT red/yel center tap. These power grounds should not rely on the chassis for current flow back to the PT red/yel center tap. This power ground lug should be physically located near the PT and cap can. You can eliminate one of those terminal lug strips."
See 2nd attachment ZZ-AC15 Ground Scheme V2.0
As part of my latest changes I am implimenting a change to the PI ground per Willabe:
"And since this amp has no -FB loop, I'd try moving the PI ground from the power amp ground to the preamp ground. "
See 3rd attachment ZZ-AC15 Ground Scheme V2.1
I am almost done with the 3 changes:
1) Re-route the yellow OT speaker wire around the chassis to the output jack
2) Move the PI ground from the power amp ground to preamp ground
3) Re-wire the red Top Cut wires as tightly twisted pair, precisely positioned wrt to the board and pot
Stay tuned...
...
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Try lifting the EL84 grid wires up in the air and see if that makes a difference.
And try moving that OT secondary wire with a wooden chop stick, on both ends, 1 end at a time and see if that makes a difference. You have to do this with the amp on.
Look at Slucky's lead dress at the EL84 tubes and try to get yours closer to that.
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I am almost done with the 3 changes:
1) Re-route the yellow OT speaker wire around the chassis to the output jack
2) Move the PI ground from the power amp ground to preamp ground
3) Re-wire the red Top Cut wires as tightly twisted pair, precisely positioned wrt to the board and pot
Do them 1 at a time and test the amp to hear any change.
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The control panel grounds (I used a buss) and the NOR and VIB board grounds should all tie together to a chassis ground lug that is mounted very near the input jacks. The chassis will provide the return connection to the PT red/yel center tap.
Did you install a chassis ground lug close to the input jack?
I don't see it on your drawing?
The PT high voltage plate wind CT should go -directly- to the 1st cap can ground, soldered to the can's ground lug, then run a wire to the power amp grounds, like you have.
And the green/yellow PT ground wire that goes to the AC power cord wire/ 3rd safety ground wire, is that the heater CT?
If so that should go to the power grounds.
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Stay tuned...
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I sure am! This debug has been an interesting one, I'm pulling for you to figure it out!
I am almost done with the 3 changes:
1) Re-route the yellow OT speaker wire around the chassis to the output jack
2) Move the PI ground from the power amp ground to preamp ground
3) Re-wire the red Top Cut wires as tightly twisted pair, precisely positioned wrt to the board and pot
Do them 1 at a time and test the amp to hear any change.
Right this could help isolate the issue so you can trace its origins and avoid similar issues in the future. Also important for catching any new issues that could arise from these changes right away so you're not adding more mystery issues that have to be debugged.
I wonder if there is a gremlin living near that workbench. Have you tried the amp in another room? Or, even better, take it to another location. Same behavior?
This is a great thing to check as well. Any luck trying the amp elsewhere, away from your work area and hopefully in a new location to make sure you're not experiencing noise unique to the area you've been testing in?
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I am almost done with the 3 changes:
1) Re-route the yellow OT speaker wire around the chassis to the output jack
2) Move the PI ground from the power amp ground to preamp ground
3) Re-wire the red Top Cut wires as tightly twisted pair, precisely positioned wrt to the board and pot
Do them 1 at a time and test the amp to hear any change.
Too late. I had already gone to distance on these changes so all were implemented at the same time.
Hum still present, no change.
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Try lifting the EL84 grid wires up in the air and see if that makes a difference.
And try moving that OT secondary wire with a wooden chop stick, on both ends, 1 end at a time and see if that makes a difference. You have to do this with the amp on.
Look at Slucky's lead dress at the EL84 tubes and try to get yours closer to that.
Did this. My EL84 wiring looks like Slucky's as far as I can tell. Moving wires with a chopstick yielded no changes in the hum.
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Try this now;
Try lifting the green(?) EL84 grid wires up in the air and see if that makes a difference.
And try moving that OT secondary wire with a wooden chop stick, on both ends, 1 end at a time and see if that makes a difference. You have to do this with the amp on. You already moved this wire.
Look at Slucky's lead dress at the EL84 tubes and try to get yours closer to that.
And the green grid wire should not be laying alongside that blue plate wire.
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And then this;
The control panel grounds (I used a buss) and the NOR and VIB board grounds should all tie together to a chassis ground lug that is mounted very near the input jacks. The chassis will provide the return connection to the PT red/yel center tap.
Did you install a chassis ground lug close to the input jack?
I don't see it on your drawing?
The PT high voltage plate wind CT should go -directly- to the 1st cap can ground, soldered to the can's ground lug, then run a wire to the power amp grounds, like you have.
And the green/yellow PT ground wire that goes to the AC power cord wire/ 3rd safety ground wire, is that the heater CT?
If so that should go to the power grounds.
The safety ground chassis connection should always be alone, nothing else connected with it.
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The control panel grounds (I used a buss) and the NOR and VIB board grounds should all tie together to a chassis ground lug that is mounted very near the input jacks. The chassis will provide the return connection to the PT red/yel center tap.
Did you install a chassis ground lug close to the input jack?
I don't see it on your drawing?
Yes. It is the 5 lug terminal strip. It is below the input jacks.
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The PT high voltage plate wind CT should go -directly- to the 1st cap can ground, soldered to the can's ground lug, then run a wire to the power amp grounds, like you have.
I'll need to make that change, it is on my list of changes (to be made one at a time :icon_biggrin:).
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And the green/yellow PT ground wire that goes to the AC power cord wire/ 3rd safety ground wire, is that the heater CT?
If so that should go to the power grounds.
Yes it is. That is the way it is on Slucky's (per the Big Guts picture).
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Try this now;
Try lifting the green(?) EL84 grid wires up in the air and see if that makes a difference.
And try moving that OT secondary wire with a wooden chop stick, on both ends, 1 end at a time and see if that makes a difference. You have to do this with the amp on. You already moved this wire.
Look at Slucky's lead dress at the EL84 tubes and try to get yours closer to that.
And the green grid wire should not be laying alongside that blue plate wire.
I lifted the green grid wires up away from the other wires. No change.
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And then this;
The control panel grounds (I used a buss) and the NOR and VIB board grounds should all tie together to a chassis ground lug that is mounted very near the input jacks. The chassis will provide the return connection to the PT red/yel center tap.
Did you install a chassis ground lug close to the input jack?
I don't see it on your drawing?
The PT high voltage plate wind CT should go -directly- to the 1st cap can ground, soldered to the can's ground lug, then run a wire to the power amp grounds, like you have.
And the green/yellow PT ground wire that goes to the AC power cord wire/ 3rd safety ground wire, is that the heater CT?
If so that should go to the power grounds.
The safety ground chassis connection should always be alone, nothing else connected with it.
I can change this. It is added to my list.
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Did you use Cliff jacks for your speaker jacks?
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Did you use Cliff jacks for your speaker jacks?
No. Only for the input jacks.
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What is the ground for in the red circle?
Exactly how many ground connections to the chassis do you have, 2, 3, 4, 5?
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Can we see some pictures of the whole amp, inside? And I'd like to see where the speaker jacks are and whats next to them.
And some pics of the back side of the chassis, showing the PT/OT?
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What is the ground for in the red circle?
Exactly how many ground connections to the chassis do you have, 2, 3, 4, 5?
That was Ground Scheme 1.2 (i.e. part of a partial implementation og Slucky's suggested changes to the grounding scheme).
I later re-did the entire ground scheme (GS 2.0), this chassis ground connection is no longer there.
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Exactly how many ground connections to the chassis do you have, 2, 3, 4, 5?
Four as follows:
1) AC Power Cord Ground
2) Power Amp Ground
3) Control (Preamp) Ground #1 (volume pots)
4) Control (Preamp) Ground #2 (Effects and inputs)
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Can we see some pictures of the whole amp, inside? And I'd like to see where the speaker jacks are and whats next to them.
And some pics of the back side of the chassis, showing the PT/OT?
Will do.
I have been trying to catch up on all the replies on this thread, and I need to complete the power section changes you suggested first.
Pictures will be later today.
thx!!!!!!
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3) Control (Preamp) Ground #1 (volume pots)
4) Control (Preamp) Ground #2 (Effects and inputs)
Chassis grounds 3 and 4 should be combined together into 1 ground.
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Can we see some pictures of the whole amp, inside? And I'd like to see where the speaker jacks are and whats next to them.
And some pics of the back side of the chassis, showing the PT/OT?
Will do.
I have been trying to catch up on all the replies on this thread, and I need to complete the power section changes you suggested first.
Pictures will be later today.
thx!!!!!!
Pictures are ready for viewing at:
https://www.flickr.com/photos/23805934@N02/albums/72157690742479393
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3) Control (Preamp) Ground #1 (volume pots)
4) Control (Preamp) Ground #2 (Effects and inputs)
Chassis grounds 3 and 4 should be combined together into 1 ground.
I'll work on that.
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What is the ground for in the red circle?
Exactly how many ground connections to the chassis do you have, 2, 3, 4, 5?
That was Ground Scheme 1.2 (i.e. part of a partial implementation og Slucky's suggested changes to the grounding scheme).
I later re-did the entire ground scheme (GS 2.0), this chassis ground connection is no longer there.
Why did you remove that ground connection? SEE PIC...
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What is the ground for in the red circle?
Exactly how many ground connections to the chassis do you have, 2, 3, 4, 5?
That was Ground Scheme 1.2 (i.e. part of a partial implementation og Slucky's suggested changes to the grounding scheme).
I later re-did the entire ground scheme (GS 2.0), this chassis ground connection is no longer there.
Why did you remove that ground connection? SEE PIC...
Both the terminal strips are connected directly to the chassis now, NOT isolated. Per Willabe I plan to combine these into a single terminal strip near the input jacks (where the 5 lug is now).
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Are all the lugs on those terminal strips strapped together?
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Sluckey meant to run the OT secondary wire around the end of the board, not all the way around to the chassis end.
Now you have that wire laying on the ac power and other things.
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Are all the lugs on those terminal strips strapped together?
Yup
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Sluckey meant to run the OT secondary wire around the end of the board, not all the way around to the chassis end.
Now you have that wire laying on the ac power and other things.
OK. I'll fix that.
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Has anything you have done today affected the top cut hum issue?
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Nope :BangHead:
I re-re-routed the yellow OT wire around the board instead of the end of the chassis.
I am in the middle of changing the two control ground terminal strips into one 7 lug under the input jacks.
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Measure resistance from pin 2 of each EL84 to chassis. What do you have?
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Measure resistance from pin 2 of each EL84 to chassis. What do you have?
Finished re-working the preamp ground from two terminal strips to one. Stay tuned for results (things have changed for the better). I will post results when I complete a set of tests.
Here are the EL84 Pin 2 resistance readings: 221k ohms on both tubes.
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since ur testing.............
play something;
remove the cap on the PA tubes cathode, play again;
Did the hum decrease with overall gain drop from pulling cap?
add a BIG cap, something 2, 3 X's bigger, gatorcippin is fine
any change
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since ur testing.............
play something;
remove the cap on the PA tubes cathode, play again;
Did the hum decrease with overall gain drop from pulling cap?
add a BIG cap, something 2, 3 X's bigger, gatorcippin is fine
any change
Hold that thought...
As I said, things have changed. I am methodically testing and documenting and will post in a bit.
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I completed all the changes discussed over the las couple of days including re-working the preamp ground from two terminals to one.
The result of this last change or a combination of the recent changes is that the HUM is gone!!!!! :icon_biggrin:
I have performed a series of tests. The details can be viewed in the attached Test Notes.PDF file.
Bottom line is I have a couple issues to address as follows:
1) Major Items
a. Effects Not Working
2) Minor Items
a. Some Nor/Vib Vol Noises
i. The noises are eliminated by setting the Top Cut above 2.5
ii. This is similar Top Cut behavior when the loud Hum issues was present
I think the effects issue will be solved fairly easily as they worked before I did a last few changes, so I (think I) know where to focus.
The other Volume related noises are a nuisance and seem related to the gremlin we have been chasing. But I'll keep working it.
Thanks for all the help so far EVERYONE, especially Slucky and Willabe. :worthy1: REALLY appreciate it.
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BTW: I think that the one change I made that might be the fixer was moving the PI ground from the power amp ground to the preamp ground.
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:thumbsup:
gonna :hijack1: for a quick clarification
Since PP PA's tend to noise cancel, would the "sharing" of cathode parts "lessen" that cancelation :dontknow:
thanks
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:thumbsup:
gonna :hijack1: for a quick clarification
Since PP PA's tend to noise cancel, would the "sharing" of cathode parts "lessen" that cancellation :dontknow:
That's a good question.
I would think no. :think1:
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PP PAs have common mode rejection due to the OT. This means that if the same signal appears on both inputs that signal will be cancelled in the OT. That same signal might be power supply hum. Or it might be some other stray signal/noise picked up in the air. But for it to cancel it must appear on the top and bottom of the OT. For it to cancel perfectly, it must be identical. This is one reason that it's important to have equally balanced tubes and perfect OTs. I don't think a properly bypassed cathode resistor will be a factor.
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OK, back at the bench.
I found the issue with the effects not working. As soon as I looked at that area closely I saw that I have the depth pot slights twisted off center, causing the resister between the speed and depth pots to make contact with the right post of the depth pot. A quick straightening of the depth pot corrected the situation.
So the only remaining issue is the minor Volume Pot noises. With the top cut turned up past 2.5, these are eliminated.
I am calling it good until someday these bother me enough to dive in some more.
Thanks for everyone's help. You all have been super helpful and relentless. I hope I can be as helpful to someone with issues I can help with.
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You really did a super job on this project. I hope you enjoy it. I know Ed's gonna start talking Celestion Blue so I'll kick it off for him. They are pricey but they bring out a lot of good in this amp, especially the EF86 channel.
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You really did a super job on this project. I hope you enjoy it. I know Ed's gonna start talking Celestion Blue so I'll kick it off for him. They are pricey but they bring out a lot of good in this amp, especially the EF86 channel.
I was going to put this atop my Fender Custom Shop 2x12, but I like the idea of a speaker that is "One of the most famous speaker voices of all-time, helping to define the '60s British Invasion". Just ordered one on Amazon that will be here on Sunday.
Thanks again!!!!!
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Glad you got everything squared away finally! Way to stick it out and trouble shoot that hum :thumbsup:
Any vids or audio of what this thing sounds like now that you're done? Let us bask in the glory of that classic EL84 overdrive lol :headbang:
Also I'm curious how your EF86 channel sounds. Working on an amp project with EF86's in the preamp myself right now and I'm curious how other people are finding the sound to be in their amps.
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Finished my head and speaker cabinets today.
Amp - https://www.flickr.com/photos/23805934@N02/47567024481/in/dateposted-public/
Head - https://www.flickr.com/photos/23805934@N02/47567023881/in/dateposted-public/
Speaker - https://www.flickr.com/photos/23805934@N02/47567023831/in/dateposted-public/
Celestion Blue - https://www.flickr.com/photos/23805934@N02/47567024071/in/dateposted-public/
Sounds amazing. The normal channel is really loud, responsive and the overdrive is awesome. The Vib channel is also great. Alot less volume, but the analog vib/trem effects sound great.
I am used to the vintage Fender amps I have been building, what a difference. I still like the Fender sound, but this is really a different ballgame.
I also tried plugging the amp into my Genz Benz 2x12 speak cab. Sounds really different, but it is a ported cabinet. The G/B sounds bigger, the Celestion Blue (in a sealed cab) sounds a lot tighter.
Anyway, I am really glad I did this project. I love the amp, I learned a ton and REALLY appreciate and respect the folks who helped me out begugging this beast.
Glad you got everything squared away finally! Way to stick it out and trouble shoot that hum :thumbsup:
Any vids or audio of what this thing sounds like now that you're done? Let us bask in the glory of that classic EL84 overdrive lol :headbang:
Also I'm curious how your EF86 channel sounds. Working on an amp project with EF86's in the preamp myself right now and I'm curious how other people are finding the sound to be in their amps.
I'll see about posting some video, I am relatively shay about my playing So I'll see.
As for the EF86 channel, it is nothing like the Fenders I have been building. As I said above, this thing is really loud, responsive and overdrives really early when [playing with a heavy hand, and clean when lightening up the play.
In my opinion, you cannot go wrong with the EF86.
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Very nice! I like putting the chassis on display in that head.