Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tubenit on December 21, 2013, 03:09:38 pm
-
I changed my 56T Plus into a Tweed BluezMeister with 5879 & CF OD. The 56 T Plus was a really good sounding amp (& maybe my favorite for playing just rhythm), but the OD stage was subtle. And the mid boost was noticeable but not a big shift in tone.
So, I rewired the first two preamp tubes into a different order.
Very dramatic difference between clean and OD now! This amp probably has the most sustain and overdriven tone of my 3 amps. I am thinking this is because the 6V6's may are being pushed as well as the preamp stages. With the OD & mid boost engaged, I can almost sustain into feedback on any note. The overdrive is not muddy sounding at all. It has a very clear cranked, pushed overdrive tone.
The OD sounds very pushed and overdriven compared to my Tweed BluezMeister (original) and the D'Mars ODS. The overdrive on those two amps have very smooth and nice sustain which is very clear sounding. This TBM with 5879 has a FAT pushed overdrive tone that is quite different. It is not gritty but it sounds more cranked.
I have mentioned it before but I am convinced that the 5879 in an OD gain stage really benefits with a cathode follower with it. This is the first time I've tried a mosfet cathode follower with a 5879. It has nice compression to it.
The amp sounds really huge for a small amp, IMO. I think it has some of that Bonamassa type cranked OD tone using a delay with it.
Anyhow, thought I'd share the schematic and layout. I will try to record the OD sometime next wk or wkend IF I can get the OD to record OK.
with respect, Tubenit.
-
Sooooooooooo that's what you been up to,looks good. :icon_biggrin:
-
Sweet.I wanna hear it.Why are the 6v6s and power section not in the layout?
-
Why are the 6v6s and power section not in the layout?
It's just the way I have typically drawn them. I'm really just drawing a layout board connected to pots, switches and tubes.
On the SCH schematic that I attached, it does show the power section & B+ rail on the 2nd page.
with respect, Tubenit
-
Well, I'm just gonna consider this a personal Christmas present :icon_biggrin:
I'll have to wait a couple weeks to unwrap it,,,that's all
Thanks,,,as always for ALL that you do!
-
Jeff -
Have you had a chance to make a sound clip of this latest build? I always enjoy your playing, whenever you are able to make them.
I can't get around to reading all the posts, but yours are among the first. Fine business.
Jack
-
I drew up a Hoffman style board for the amp design.
SCH versions is here: http://www.el34world.com/Forum/index.php?topic=16449.0 (http://www.el34world.com/Forum/index.php?topic=16449.0)
CHECK for errors!
with respect, Tubenit
-
Looks like a good Christmas present to yourself I have found those are always what you want . :icon_biggrin:
Bill :m11 :occasion14:
-
Here's a concept drawing that I made of Jeff's circuit, using a triode as the CF. And rather than his PI, I used the second triode in the tube as a Cathodyne PI. Saved adding another tube. The PI was taken from Merlin's book.
Forgive the unconventional schematic. I draw literally like it might be a P2P build, using actual tube internal layout taken from data sheets.
Look to my V4 for the CF and PI. There are a couple other differences, but the CF and PI are the major ones.
Jack
03Jan14 - Note: See below for rev-C.
-
GREAT idea!!! I like it.
I have a couple of questions (indicated in yellow):
1) looks like the 5879/CF is bootstrapped .............. correct? (this may be a challenge switching from clean to OD because of the
volume boost)
2) the 470k grid resistor and the 47k grid resistor to cathode ..................... did you mean to reverse those?? 47k grid resistor
and then 470k grid resistor to cathode?
EDIT: per Merlin's article, you have drawn it correctly! http://www.freewebs.com/valvewizard/cathodyne.html (http://www.freewebs.com/valvewizard/cathodyne.html)
I indicated in light green some component values that you might consider changing IF you want something of a tighter and more focused bass response. Not necessarily better just another option in values to consider. The 220p smoothing cap across the plate, I would use for added smoothness. These changes do get the "clean" channel closer to Fendery clean tone, IMO.
With respect, Tubenit
-
Ok.
To question 1 - Yes, bootstrapping is where I was headed with that mod. As to the challenge, I just don't know as this is the first draft and no build to prove it out.
To question 2 - I applied Merlin's configuration for the Cathodyne PI:
http://www.valvewizard.co.uk/cathodyne.html (http://www.valvewizard.co.uk/cathodyne.html) .
Look at the very bottom of the page and note that he has the grid stopper as a 470K and the grid leak as a 47K. He gives an explanation for the grid stopper, but I may have missed his reasoning for the 47K value of grid leak. Also, notice the diode in series with the 47K, that Merlin recommends for arc protection, found in the bottom of this page:
http://www.freewebs.com/valvewizard1/dccf.htm (http://www.freewebs.com/valvewizard1/dccf.htm) .
As to your other suggestions of component changes, I have saved you drawing to the same folder as I have the other TBM drawings. This will be as far as I can go (drawings), for now.
I really appreciate your looking my drawing over. I've only proof-read it a couple times, but will do so again. I tend to get component values and labels askew, when a schematic is this busy. But, I think that it's reasonably complete.
Take a look at my NFB. Though I don't see it on your rendition, I brought mine back to the FX Return side cathode of my V2. I did not include a means to switch it out. I chose the value that you used. I have another P-P that I used a 33K in the NFB, and brought it all the way back to the 2nd of three gain stages. That one has a Cathodyne PI in it. If and when I have that one open again, I may try your 27K, as it has a bit more gain than I want.
Again, thanks for the comments and suggestions. Have a good one.
Jack
Note: You added your edit before I could post my response. Glad you saw it. Thanks again, for the comments.
-
Tubnit- "I think it has some of that Bonamassa type cranked OD tone using a delay with it."
I had heard of Joe in the past but really knew nothing about him. Somehow I ended up on this link: http://www.youtube.com/results?search_query=joe+bonamassa+just+got+paid+royal+albert+hall+2013&sm=1 (http://www.youtube.com/results?search_query=joe+bonamassa+just+got+paid+royal+albert+hall+2013&sm=1)
I've played this video about 20 times since and try to hammer it out every other time I practise. Great guy, HUGE SOUND. Joe is also one of those really nice individuals in the music Arts. I won't say industry since his manager produces all their music outside of the mainstream.
Sounds like a winning design. Can't wait to hear it.
Silverfox.
2014- We made it!
-
Here is the complete drawing, with power supply. Please check for errors. And note, I placed a Hum Balance pot in place of the two 100R's that you have on your 6.3v filament winding. This works very well in my Ampegs, fixed bias or cathode bias. In the cathode biased models, they connect the wiper to the cathode junction of the power tubes, like you would if using the individual resistors. Take a look.
Jack
03Jan14 - Note: See below for rev-C.
-
Thanks for sharing this, Jeff! I'm going to try this one out. Do you find that the mosfet works ok without a gate stopper resistor? I see a lot of people add a ~220R there.
-
Take a look at my NFB. Though I don't see it on your rendition, I brought mine back to the FX Return side cathode of my V2. I did not include a means to switch it out.
I think that will work fine. I would suggest the NFB switch. I very seldom play mine with the NFB engaged. And there is a significant difference in sound between off/on with NFB. It's a somewhat more aggressive/pushed tone without the NFB.
Do you find that the mosfet works ok without a gate stopper resistor? I see a lot of people add a ~220R there.
Just an error in the schematic drawing I posted. There is a 220R/2w resistor there like on the D'Mars.
Restating something ............ there is a BIG difference in tone between the clean and OD. And the clean tone really is a nice warm clean sound. I can not imagine anyone not being able to tell what is which with a "blind test". Same thing with the mid boost. You can easily hear the difference. That makes those features very useful, IMO.
With respect, Tubenit
-
I think that will work fine. I would suggest the NFB switch. I very seldom play mine with the NFB engaged. And there is a significant difference in sound between off/on with NFB. It's a somewhat more aggressive/pushed tone without the NFB.
Not sure how to approach this with my configuration. Just a simple switch, to take it in and out? Or, should there be more?
Jack
-
Regarding the NFB switch...............
Yes, a simple spdt. It's in the original schematic at the top of the thread.
I am in the process of drawing up a layout board to go with your schematic. Will post probably tomorrow Thurs am.
With respect, Tubenit
-
Ok. I saw how you have yours. But, I meant to ask if I should include the paralleled capacitor and resistor, that you show on one leg of the switch. Rather than just a NFB disconnect.
Looking forward to the layout. Thanks the the fine work. Have a good one.
Jack
-
Ok. I saw how you have yours. But, I meant to ask if I should include the paralleled capacitor and resistor, that you show on one leg of the switch. Rather than just a NFB disconnect.
My apology, I am not sure how you'd hook up that NFB. I am inclined to think about leaving it out. IF you need something cleaner in tone, you can use LNFB around V1b like on Dumblish amps.
with respect, Tubenit
-
First, let me say that this is an interesting thread!
Which tube stage is driven to saturation when switched to OD?
From just looking at the schematic, It's hard to know since the trim pot before the pentode could very well be trimmed down quite low such than the difference in gain between the two switch positions ( as the signal exits the dpdt SW) is slight (10% 20%). If this is the case, maybe it's the 6v6s that are over driven?
Or if the trim pot delivers a decent signal to the pentode, is the signal that exits the pentode and hits the 500k level pot a clean sine wave ? Or squared off (I.e. saturated)? If it's clean, is it the first 12au7 in the fx segment that is driven to saturation?
-
Which tube stage is driven to saturation when switched to OD?
As far as I know Jack Hester's TBM 5879 OD is a draft and has not been built.
With mine which has an LTPI instead of concertina phase invertor, I think most of the OD is from the 5879 since it has a very clean tone prior to switching the 5879 in. However, as one cranks the amp ........ I would expect the 6V6's to become more overdriven also.
On these type of high gain amps, you can't really crank every knob to "10". It just doesn't sound right. So on mine, the clean volume is at 5, treble 5, bass 7, mid 3, OD trim 6, OD volume 7, FX send 5 & FX level 6-7.
I've never owned an oscilloscope, so that is the best answer I can give you.
With respect, Tubenit
-
Which tube stage is driven to saturation when switched to OD?
With mine which has an LTPI instead of concertina phase invertor, I think most of the OD is from the 5879 since it has a very clean tone prior to switching the 5879 in. However, as one cranks the amp ........ I would expect the 6V6's to become more overdriven also.
On these type of high gain amps, you can't really crank every knob to "10". It just doesn't sound right. So on mine, the clean volume is at 5, treble 5, bass 7, mid 3, OD trim 6, OD volume 7, FX send 5 & FX level 6-7.
You have a total of five gain controls (all the ones you've mentions except treble, bass,mid). the FX send and FX level are both independent master volumes of sorts (esp. if nothing is plugged into the FX loop). If you have 'FZ send' set to 5, the signal is being attenuated first 50%, and then about 60% with the 82k/100k "fixed" voltage divider (with nothing in the FX loop, that's 30% attenuation). the 12au7 driving the 250k FX-level make-up pot, with pot set to 6, is probably a total gain of 4X or 5X ? So, its possible all the OD crunch is in front of the 6V6s.
With clean-vol=5 and OD-trim=6, it seems to be very possible that the pentode is not being driven to saturation, but rather the first 12au7 triode is., especially if the total sound produced by the amp with the OD-SW=off is clean (with those same clean-vol and FX-vols settings).
None of this is a bad thing, especially if you are happy with the results (the only reason I bring it up is that I'm interested in understanding the circuit).
Personally, I don't like to build an amp that can't have all knobs set to 10 simultaneously, because,, well, if left unattended in the hands of another musician, they will all get turned to 10! On the other 5879OD thread, I mentioned using the 2nd half of the dpdt to switch in a resistor on top a volume pot that comes later in the circuit. For example, if you take the 100k FX-send pot that you set to '5', you could switch in a 100K resistor on top of that to produce the same 50% att. at max knob switch, thus giving you greater tune-ability on that pot, and the ability to crank it to 10. Instead of the FX-send, you could do the same with your final master FX-level.
-
Personally, I don't like to build an amp that can't have all knobs set to 10
I have no doubt, some individuals like to roll all the knobs to "10".
:icon_biggrin:
However, & just a personal preference .......... I have never played or owned any amp where I liked everything on "10". I have found much more musically sweet tones with pots dialed more from 3 or 4 to 7 range typically.
With respect, Tubenit
-
I checked this thread a couple times today from work, but was unable to comment. Shorthanded on help, and major busy starting up two of our generating units.
Anyway, that's a great layout drawing and schematic. And, I have a question about your turret/tag board.
When you make a layout for one of your amps, do you have some standard for board size dimensions? I buy blanks, sometimes fixed lengths from Doug, sometimes a large sheet from other sources, and cut them to fit whatever is needed. On my little table saw with a tile blade. Or, on a little Rockwell BladeRunner using a fine toothed metal cutting blade. I have some tile blades for it, but they make a cut that is way too wide.
My point is that yours seem to have some set size. I just picked up a generic, pre-drilled board off of the bench that I've been threatening to use on something. It is 10-1/4" x 3-1/8", 27 holes x 8 holes, at a 3/8" spacing.
Your layout would be 28 holes by maybe 6 holes, if I were to use the same spacing. I've never used one of these pre-drilled boards before, as I drill only what I need. But, this one may be suitable for me to try out on this build, though I'm thinking that I may want to shave 2 holes width off, lengthwise. Or, I may leave one set of holes empty down each side, and route wires through them.
On some of my simpler builds, I've taken the schematic like I posted earlier (smaller build, of course), plot it to scale on a sheet of paper, tape the paper over the board, and center-punched it though the paper. Drill the holes for turrets and mounting, and do the build just like it's drawn. No schematic needed after that, as you can literally follow it on the board. I've got a small AM radio transmitter that I plan to do this way, as it is ever so simple.
But, back to your layout. What would be your physical layout for what you've drawn? Thanks for the fine work.
Jack
-
Jack,
I have used Doug's tagboard dimensions ............ but his turret board materials.
In other words, the turret layout and size of the board matches the tagboard. I just use a hacksaw and cut the turret board material to a narrower width. I actually like Doug's Hoffman style turret boards ................. however, a paralleled turret board is easier to work with for an experimental build where one may be changing a lot of things around.
I had a small scrap leftover piece of the tagboard that I used to trace the size and the hole spacings.
This tag board has 2 rows of tags x 28 tags per row
The length and width are 300mm x 56mm or 11.875 x 2.25 inches
http://www.hoffmanamps.com/MyStore/perlshop.cgi?action=template&thispage=BoardBuilding&ORDER_ID=968932707 (http://www.hoffmanamps.com/MyStore/perlshop.cgi?action=template&thispage=BoardBuilding&ORDER_ID=968932707)
Hope that helps. with respect, Tubenit
The attached picture is mostly a paralleled turret board but with a few added turrets where needed.
-
Yikes! (in the previous drawing), I discovered that I had drawn the bootstrapped 5879/CF incorrectly. Hopefully, this is correct.
CHECK for errors! If there is a discrepancy between the layout and the schematic, go with the schematic.
With respect, Tubenit
-
Ok. On the turret board construction, the standard is really the application. Most of the pre-fabricated boards that I've seen are 3-1/8" wide, by whatever length. And, I buy those on occassion. But mostly, I like to cut the width and length to the application.
Another observation on the pre-drilled board. The holes are large, so I'm thinking large turrets or eyelets. I typically use smaller turrets, with an occassional large turret or eyelet. But, for the sake of this experiment, I can use large. Plenty of room for multiple components, if needed.
Good catch on the drawing. I'll save your update to my computer when I get home this evening. Thanks for the continued fine work on these drawings. Have a good one.
Jack
-
IF you wanted to .......... you could just use Doug's tagboard for under $7. :dontknow:
Only disadvantage is that they aren't as sturdy as his turret board material and turrets.
With respect, Tubenit
-
IF you wanted to .......... you could just use Doug's tagboard for under $7. :dontknow:
Only disadvantage is that they aren't as sturdy as his turret board material and turrets.
I would, if I didn't already have materials on hand. This pre-drilled board needs using, and I've got a large quantity of turrets and eyelets that will go in fairly quickly. I'll hold off until everyont has had a chance to look the drawings over. I plan to drop the NFB from my drawing, as per your comments on the lack of need.
I think that I have a generic aluminum chassis that I could use, though I don't have a cab. If I can put my hands on a plate to cover the bottom of it, I'll just put rubber feet on it, and let it be one that can be passed around. That way, I have a number of friends who would love to give it a tryout. Especially a couple of guys over in Durham. One of them would make some sound clips for me.
It's all pending on time, and a busy work schedule. I'll post anything that I do, with pics. Thanks for making this good stuff happen. More to come. Have a good one.
Jack
-
I have reconciled my drawing to reflect Jeff's changes, though I left one decoupling cap in the power supply to a value of 16uf (C27), as in the original drawing. Jeff had changed it to a 26uf, and I'm thinking a typo. Please confirm.
I also made a correction on my Mid pot location, to reflect the same circuit as Jeff's. I added the cap around the 33K resistor (C17) above the 5879 tube, and the cap around the 68K (C20) above the PI.
There are a few component value changes, to reflect his values, and I left my Hum Balance pot in place.
I left the OD triode CF and the PI triode in the same tube (V4) as a 12DW7, making my CF the same as a 12AU7 and the PI the same as a 12AX7. This one might be better as a 12AU7 tube, but I can experiment.
I left the active FX loop the same as Jeff's original, both triodes in one tube (V2). But, can experiment here, as well, with different tubes.
I will draw the layout as Jeff has drawn it, and add my component labels. I have had to correct my labeling several times, as I reconciled to his. So, I need to be sure that I have my layout just like his, drawn to fit this pre-drilled board. I'll have that on the same drawing as the rest of what I've done.
I've got to go in at Midnight and work until 8am tomorrow. Cold weather coverage at the plant. Found that out just after noon. It gets bone chilling cold down there on the water, and we're headed for the teens in temperature, tonight. If all is quiet, and nothing freezes, we stay shut up out of the cold, until called. Maybe I can make the layout drawing, then. We'll see. If not, tomorrow, after I'm home and have had a nap.
I'm posting my changes, up to this point. And, will post the drawing with the layout (with component labels), when that one is finished. Have a good one.
Jack
11Jan14 - Note: See below for rev-D.
-
Jeff had changed it to a 26uf, and I'm thinking a typo. Please confirm
Actually, I did change it. But as I said previously, some of the changes are just different and not necessarily better. This can be viewed as one of those. It simply tightened the bass response on that tube somewhat. The original 16uf is just fine.
With respect, Tubenit
-
It's been a spell, but today (Sat) I was able to finish my layout. Once again, modeling after Jeff's drawing, I set upon the task of making it reflect my tube lineup. Because I have a different configuration than Jeff, I had to shift components in my layout. And because making these type drawings are not easy for me, I really appreciate having his, to set the stage for mine.
Anyway, I tried to make mine follow convention as much as possible, though I tend to still draw literally as if I were building from a scaled drawing. Here is that first draft, with my previous schematic. I'm thinking that I will go back and do a schematic that, too, follows convention. But for now, here's what I have.
Again, Jeff is to have all the credit for the work.
Note: When I do complete my new schematic, it will have a corrected component labeling (updated numbers). Also, the pre-drilled board that I used to set the dimensions for this layout has holes that have 3/8" spacing.
More to come. Have a good one.
Jack
12Jan14 - Note: See below for update to rev-D.
-
Jack,
THANKS for sharing your work and drawing. It looks great! And I think you're going to have an incredible build.
From my perspective, this is totally your amp design with the triode CF and the concertina phase invertor. Please feel free to rename the amp anything that suits you.
:thumbsup: :thumbsup:
With respect, Tubenit
-
A fellow on another forum has offered me an empty Silvertone 1482 cab, that appears to be in very nice condition. It has no chassis or speaker, but may serve as a likely candidate for this build. That just came about this afternoon, so the timing was perfect. I'm no woodworker, and this may enable a nice old cab to be pressed back into service with a new purpose.
You'll notice that I put board dimensions on the drawing. I didn't indicate the gap between boards, but I made it 1/4". So, not knowing cabinet space available, I may or may not be able to use this type for the supply. A canned cap may be in order, with the resistors mounted on the terminals. We'll see.
I may take my lead on a power supply from some that I see in older amps. One that comes to mind is a Gibson GA-78, that has the power supply in the bottom of the cabinet, and a harness feeding the amp, which is mounted in the top. As this Silvertone cabinet has the chassis to one side, the power supply could be mounted opposite of it. Just an idea, as I don't know how much the speaker would crowd it.
A question about the transformers that you use. Do you have the spec sheets for them (PT, OT)? Mostly, I need the footprint, to figure their placement. I've got several nice ones, taken from trashed amps/radios, that I've marked with known information. However, most are very large. But, I like to re-use such when I can. For the sake of the drawing, I like to put modern specs on it. Others may take an interest, but only have access to new.
Anyway, I'll plan to start on the schematic, tomorrow after Church. I'll post that revision soon. Have a good one.
Jack
-
I updated the drawing, and left it as the same revision. The major change was to correct the component labeling to have sequential numbers.
I found an error where I had a ground in the wrong place on the Tone Stack.
I had to add a missing capacitor to the Volume pot, giving it the next highest number (C29)., rather than shifting them all.
I also added a missing resistor (R35) to the PI.
Other than these changes, I believe that it can be considered ready for construction. Please look it over and comment with errors found, or improvements. Every time that I think that I'm done, I seem to find one more thing. Hopefully, that's not the case now.
Jack
13Jan14 - Note: See below for rev-E.
-
I'm thinking that this will be the last update, before a build. I managed to put together something of a standard schematic. It's still not entirely like most, but it's a start.
So with this revision, I have included the layout, the new schematic, my original format schematic, a Bill of Materials, and a complete sheet of the entire drawing. I only drew the power supply once, as it's simple enough, as is.
I probably won't put a board together, or populate it, for a couple weeks. My work schedule has me working before daylight until after dark each day, starting Thursday. I had today off, and decided to stay in to head off a cold. But, I'll try to make a start when the long hours are behind me. Maybe I'll have the Silvertone cabinet in hand, to plan a chassis, and possibly a separate power supply.
I'll post my progress, as it comes together. Have a good one.
Jack
Note: C29 is now on the BOM and the new schematic (Vol pot R14). Also, added the Hum Balance Pot to the Layout
-
Question for Tubenit.
Meant to ask it earlier, but do you use new tubes in your builds like this? Or, old stock tubes? Thanks.
Jack
-
Jack,
I've been reading along the whole time and really appreciate all of your work....
I'll be experimenting with this circuit in the upcoming weeks and trying a few of your ideas in conjuction with the original design.
Let me know if there is anything I can do for you as far as comparing notes.
Thank you for sharing all of your hard work....it looks great! :thumbsup:
-
Let me know if there is anything I can do for you as far as comparing notes.
Actually, I thought of making another quick sketch of a fixed bias power section, with independent adjustable bias to V5/V6. But, decided to quiz Jeff as to why he chose the cathode bias on many of his designs. Maybe all of them. I hadn't got around to it, but now is as good of a time, as any. I'm curious as to how the two compare, in voicing.
Other than that, from your bread-boarding thread, I believe that you could answer a point (very soon) that he brought up about a possible volume jump. That is, when switching to OD.
When following my drawing(s), please comment on any discrepancies that you may find, so that I can correct and publish. I think that I've look at it too many times. Fresh eyes would be a big help.
Other than that, post lots of pictures and sound-bites. I'm very satisfied that Jeff's original circuit will perform as it should, as it's based on proven circuits. The little bit that I deviated from his original is based entirely on an idea, and nothing to back it.
Jack
-
I use a mix of new and old tubes. Usually NOS 5751's. New 12AY7's. Old 12AV7's. New 12AX7's. New power tubes. Usually new rectifier tubes unless 5Y3GT which will only be NOS or OS.
I like cathode bias tone. PRR stated some stuff about it on the forum yrs ago that convinced me more that's what I wanted. I am not trying to go for more loudness and what I end up with using cathode bias is plenty loud for me. Any of the quasi-pseudo pretend original designs I've come up with or worked on with Geezer have only been cathode biased.
Like on my D'Mars ODS, I can use a 5Y3GT and 6K6 .......... or 5V4 and 6V6 ................. or GZ34 and 6L6 all with only switching tubes and not having to rebias anything using a 270ohm resistor & cathode biasing. I like the convenience of that.
With respect, Tubenit
-
So, mostly new tubes. I have an abundance of octals, of all sorts. I'm fresh out of old stock 12AX7's, but that's because I used them as replacements for the newer stock (JJ's, Sovtek's, GrooveTube's, etc.) that I pull from old stuff, and replace with good, old stock. So for once, I may use all new(er) stock on a build.
And, I like your reasoning/examples for using cathode bias. Makes good sense to me. I'll leave the drawings as-is, on this build. And, play with the fixed bias maybe next time.
Jack
-
OK guys, I got it up and running...after a "few" hours of straightening out a couple mistakes on my new board, and the setup of this circuit :BangHead:
This is how mine is set up currently:
SS rectifier with 335 VDC on the plates of 2 NOS GE 6V6GT's, cathode biased, with a 270ohm resistor and 100uf bypass cap, approx. 30mA bias current,,,, into a Deluxe Reverb OT,,,, using a 12BZ7 as the bootstrapped cathode follower, and LTPI... 50/40/20/20/20 filtering
-I just ordered some 6K6GT's and i'll report back when those are in,,,,,but for now, I can't get it past 2-3 without disturbing the neighbors :sad: (I shoulda seen that coming)
Here's some brief, first impression notes:
- The clean IS very Fender'ish and reminds me very much of the AB763 DR I was just playing with....I'd love to add reverb to it, because without it, it's a little dry for my taste (and playing ability)
- The mid boost control is useful and seems to make the tone rounder overall......
- The clean can get very "pushed" by cranking the effects send and return,,,, and this affects the OD channel as well, which I like...it will take a little time and knob tweaking to find the sweet spot, and balance the drive of each channel.
- I did find that I could balance the volume of the 2 channels by the setting of the OD volume control...
- Switching in the OD channel adds a strong, fat, gritty "cranked" quality, that reminds me a lot of a good Billy Gibbons lead tone, at lower "drive" settings, but gets bigger, wider, and much meaner at higher gain settings,,with a ton of sustain, and harmonic blooming.........I wasn't able to really crank it yet, but I'm looking forward to the next chance I'll get.....
It might have to go back to the shop for play testing and recording.
- I (of course) wanted to see how much oomph I could get out of it, so I tried replacing the 12AU7 in the effects loop with a 12AX7, and it just wanted to sing all day....
- Only problem is, I have an inherent noise issue with running it flat out on the breadboard like this, so I'll have to work on getting it more quiet,,,and figuring out what I can and cannot get away with, gain wise.
I'll try to get an actual schematic together as soon as I settle on a couple things...
I'm really excited to get a slight delay in the loop and really get it singing :icon_biggrin:
-
Looking forward to seeing your schematic of the finished amp. Great job on such a fast turn-around.
Jack
-
Great job on such a fast turn-around.
This is how it was possible
-
Silvergun,
VERY cool stuff you're doing there and THANKS so much for sharing it!
With respect, Tubenit
-
VERY cool stuff you're doing there and THANKS so much for sharing it!
Thank you sir,,,,call me inspired.... :icon_biggrin:
I took the board back to work today so that I could crank it and give a report....here it is:
- The amp is voiced very nicely, and although I am a tweaker at heart, I was not inclined to change or even question ANY of the coupling cap values.......good, more time for play-testing
- This is a complex amp, and although it is hard to get a bad sound out of it,,,, one way is to crank everything to 10..
the controls are very interactive, and with them all on 10 you lose any real separation of the 2 "channels" (not to mention that there is just too much gain here to have control just maxxed out)
- There IS A TON OF GAIN (OD) here, and you can make the clean stages a drive channel just by turning up the preamp gain control past 6 (1st volume), and turning the effects send up to 6 or higher,,,and adding the mid boost...at that point the clean channel has a comparable amount of gain to a stock Trainwreck express,,, cranked ......yes, I just said that
- The problem with that is that when you add the 5879 stage, you wont hear the personality of the pentode come through because it's just gain on top of gain and it crushes itself,,,,,,so you have to set the amp up the way tubenit describes "his settings", so that you can appreciate the contrast of the 2 channels (even though it's not actually 2 channels,,,you are just swithching in and adding the 5879 to the equation)
-In my attempt to get the first 2 stages a little cleaner, I ended up with a 5751 there and thought that was a perfect tube for that location....it got rid of some front end noise, and it will stay for now
- I started poking around with the scope to figure out where the most OD was coming from and saw that you could see it in a few different locations just by changing the effects send/return levels in conjunction with the input volume or the pot feeding the grid of the 5879.......so what I'm trying to say is:
-If this was my gigging amp, I would spend a month getting the settings just right and then remove all of the control knobs except for the volume going into the PI (the "master")
- The character of the 5879 is the special feature of the OD in this amp and care needs to be taken in how you use it....it adds a fatness and feel of depth and dimension that makes it stand apart from a standard 12AX7 gain stage....too much gain going in will result in that character being overshadowed.....I'm wondering if we can extract any more character from it by changing component values (my lack of preamp pentode experience stopped me from trying that)
-There was one other item worth noting....the PI itself is responsible for a lot of gain and clipping and it seemed like no matter what signal I fed into it, it was coming out squared off.....I had a 12AX7 in there, and wished I had a 12AU7 handy because I would love to try it in that spot....I think that the PI gain could be lowered because the input sensitivity of the 6V6s is pretty high........
I guess that's it for now.....I'll try an AU7 in the PI tomorrow and see what I see....I'll let you know...
Hope that wasn't too much rambling, but I wanted to get that typed out while it was fresh in my head because I didn't write any notes tonight......it was just a knob turner night...these are all just opinions , and first impressions that I will try to confirm with MORE testing.
The amp sounds great! :thumbsup:
-
Wow! I find your report very interesting and very helpful information. And I think we're arriving at some similar conclusions.
I have had to discipline myself to "think about" these amps in a different framework. As you said, the clean channel above 6 with mid boost has quite a bit of gain. However, a 12AY7 in V1 & at around 4 to 4.5 has a pretty clean tone to my ears.
Overly simplified, I typically use 4 to 7 range on any of the pots that are connected to the gain. Then you've got to experiment to see what the best tonal pot settings are from my experience.
Sort of an odd way to think about amps IF one is prone to rolling all the dials to "10", .............. HOWEVER, the 4-7 ranges allow one to dial in some very sweet musical and useful tones. Cranking everything to 10 loses musical sweetness and just adds a thicker layer of mud to the tone, IMO.
I am typically using a 12AY7 in V1 on these type amps but have also used 12AV7 and 5751's on occasion.
I have tried a 12AT7, 5751 (nice) and a 12AX7 in the LTPI position. I liked all of them in that position.
So far, I like 12AV7 or 12AY7 best in the FX, but have also had reasonable results with a 12Au7 and 12AT7.
Given the variety of 12A_7's and pot controls and rectifier tube choices, ........... you can really get quite a variety of tones out of one of these amps, IMO.
With respect, Tubenit
-
Given the variety of 12A_7's and pot controls and rectifier tube choices, ........... you can really get quite a variety of tones out of one of these amps, IMO.
I was thinking about this some more last night, and realized that I should have made a few disclaimers BEFORE posting my comments above...
Firstly, I should've posted an accurate schematic for what I've done because it is a slight deviation of your design,,,and any of the opinions I stated above are based off of my modified take on your design....so I apologize for any misleading info. that others may take away from this....
I know that YOU know what I mean, but I probably should've given a more accurate account of how the amp sounded before I started modifying it for more gain.....
So here's some thoughts:
- All of my statements were a result of having a 12AX7 in the effects loop, which I think is probably not "the right" tube for that spot,,,,but in my eternal search for more gain, I had immediately replaced the AU7, and never looked back........with that higher gain tube in that spot it turns the effects loop into a big gain stage which makes the send/return controls more like additional gain controls than their intended purpose of loop "balancing"
The amp sounded great as designed, I just have a tendency to immediately start modifying things towards my personal taste (maybe not the best idea for a well thought out design like this....I could've at least given it 24 hours :laugh:)...
When I get a little bit of time, I'm gonna "roll-back" the amp to stock, and try to get a sound clip done for anyone who is interested,,,,,before I go any further with my own tweaks.....
Then,, I'm thinking that maybe I should just start a new thread of this modified version, so as not to muddy the waters for guys who will just want to build strictly off of T's design....
I also don't want to confuse Jack with my "hot-rod" tendencies....I'm sure that it can be difficult to keep up with all of my random thoughts about which tubes in which positions, and which controls set where.....I'll try to do a better job of being more specific
-
I also don't want to confuse Jack with my "hot-rod" tendencies....I'm sure that it can be difficult to keep up with all of my random thoughts about which tubes in which positions, and which controls set where.....I'll try to do a better job of being more specific
I am. Confused, that is. But, not in a bad way, as I'm really enjoying your commentary. I do hope that you document your build as-is with a schematic, before moving too far from it. Gives me a better picture to carry, as I go back over your descriptions.
Otherwise, continue on with your trials.
-
On the rev-E drawing that I have posted, the Trim is in the wrong place on V3, on my conventional schematic. It should be moved to the Control Grid, and not the Cathode. It is correct on the layout and my original schematic. I made the correction on my drawing, but have not plotted. Will post, when I plot it again.
Jack
-
OK, I went back and edited that post and added my version of T's schematic....
Biggest changes you should see are filtering values, dropping resistor value (between A and B), and screen resistor value,,,besides just basic tube substitutions....some small cathode bypass cap value changes...that's it
I set up the screens like that for use with 6K6GTs,,,and to try to "simulate" some of the sag effect that is lost by using the SS rect (I based the value off of the 5E3), and the 10 watt rating of that 4.7K resistor, is overkill, but cheap, low heat insurance
Sorry I haven't taken the time to work in SCH,,,it's just easier for me to cut and paste, and this schematic will be changing.
-
I just posted a short demo clip of how the amp sounds on the board as of Sat. 2/1
I bought a new little recorder and wanted to test it out.....let me know if there is anything else you would like to hear.
I'm using a slight delay in the loop with the MIX pot installed.
http://www.el34world.com/Forum/index.php?topic=16636.msg164501#new (http://www.el34world.com/Forum/index.php?topic=16636.msg164501#new)
http://www.soundclick.com/player/single_player.cfm?songid=12671470&q=hi (http://www.soundclick.com/player/single_player.cfm?songid=12671470&q=hi)
-
I listened to the clip a couple of times and realized that I should explain a couple things....
- 5879 is switched in the whole time, no cathode bypass cap, trim pot cranked to 8
- bootstrapped cathode follower 12AT7
- Input volume on 5, treble 6, mid 7, bass 5, mid-boost switched on
- 10K shared cathode resistor in the PI, used as a power dampener, per sluckey's scrapbook (18 watt switchable power dampener)
- 12AT7 phase inverter tube
- 6K6GT power tubes installed with "master" vol. set on 6.....pretty bearable volume, sitting right in front of it
- Celestion G12H-30 in the open back, top half of one of my 2x12 cabinets
- Parallel FX mod with Mix pot on 3, and slight delay in loop....carried over from this thread:
http://www.el34world.com/Forum/index.php?topic=16606.0 (http://www.el34world.com/Forum/index.php?topic=16606.0)
-
First of all, VERY nice playing! You have some very cool chops. :thumbsup: :thumbsup:
I think the amp sounds really excellent. You're getting what I would call that "vowel" tone, very sweet harmonics and some very very nice sustain/blooming.
I agree with you that the speaker probably isn't the best choice for it. I've tried an Emminence Cannabis Rex, Emminence Texas Heat and an Emminence Red, White and Blues with it. Each of those sound good to me. The CR and the RW&B would be the smoothest. The Texas Heat gives it some "Fenderish" honk, IMO.
THANKS a bunch for sharing the soundclip. Really enjoyed hearing you play. Very tastefully done.
With respect, Tubenit
-
OK, I went back and edited that post and added my version of T's schematic....
Biggest changes you should see are filtering values, dropping resistor value (between A and B), and screen resistor value,,,besides just basic tube substitutions....some small cathode bypass cap value changes...that's it
I set up the screens like that for use with 6K6GTs,,,and to try to "simulate" some of the sag effect that is lost by using the SS rect (I based the value off of the 5E3), and the 10 watt rating of that 4.7K resistor, is overkill, but cheap, low heat insurance
Sorry I haven't taken the time to work in SCH,,,it's just easier for me to cut and paste, and this schematic will be changing.
I saved your schematic (dated 22Jan), to compare with Tubenit's. You don't have your mods drawn on that one. Is there another posted that does?
Really great sounding clip. I can only hope that an octal version comes close. Breadboard may come first. Thanks again, for that inspiration.
Jack
-
I saved your schematic (dated 22Jan), to compare with Tubenit's. You don't have your mods drawn on that one. Is there another posted that does?
No,,,, and thanks for reminding me...
I'll update and post shortly.......there are definitely a couple changes worth noting.
Thanks for the kind words Jack, and keep up the good work yourself sir.
-
OK guys,
As far as I can tell, this is the way it appears on the recording.....
Changes from previous schematic:
- 12AT7 cath. follower after 5879 (quieter than the 12BZ7 I had in there)
- 12AT7 PI
- 10K input resistor
- Parallel FX mod with 100K MIX pot
- 390ohm cathode resistor on 6K6 power tubes to bring dissipation down to 8 watts per tube....was over 9 watts with 270ohm
- 10K shared cath. resistor on PI as a power dampener "trick"
- I had tried a cathode bypass cap on the 5879 and thought it was a keeper, but then during recording I was looking to drop some noise, and I found that I thought the 5879 sounded better without it (less boxy/gritty)
I think that's everything for now........back to recording tonight :icon_biggrin:
-
I've got a couple friends that I have sent Tubenit's soundclips to, from time to time, as they like his playing style (but, don't frequent forums). Yours will go on the same mailing list, as this is a keeper, too.
Another friend who plays lead in a band, will most certainly want to hear this. He's been playing for something over 30 years now, and he will love the sound of this amp. Especially, since he's just recently started building tube amps. A really good technician, and excellent guitarist. The amp building all came about last year, when a Vox combo amp of his went South on him. And, because of the circuit board construction, and the high quote to fix it, he and I had a discussion of putting a basic clean amp inside the cab, and running his effects through that. He built it in it's entirety, in his kitchen, on the counter. And, has performed with it.
Well, that snowballed into a second clone head build of a Marshall JCM800 (I don't remember the model), that has since been tweaked and modded. He's away on a job in Florida (we're in N.Carolina), but I had mentioned your building breadboards. When I told him that I was drawing the beginnings of one, he got excited.
I'm thinking that when he gets back, a second breadboard will be in the making. Then, the serious tweaking will begin. So, between Tubenit's amp designs, and your breadboarding (with soundclip), something else will begin to snowball. He's a copier/paster, like yourself. I'll just have to keep up with his drawings, as well.
Anyway, I'm sending him the soundclip is just a minute, and I'll let you know his response. Both of y'all keep doing what you're doing. Have a good one.
Jack
-
I posted this over on the sound clip thread, BUT I feel so strongly about this, that I figured I better put it here too....
I tried a Celestion Vintage 30 in place of the G12H-30 Anniversay speaker that I have been using,,,and it just absolutely sounded terrible to my ears, with this amp.
It brought a very nasally, harsh, sharp tone that I didn't find fitting at all.
If anyone builds this amp and plugs into a V30 they are going to be missing the great tone that this amp possesses.....sadly.
-
The challenge I had with the bootstrapped 5879/CF arrangement was I could not get a balanced clean to OD tone.
So, I am wondering IF there is another way of approaching this besides the typical DPDT switching on Dumblish amps.
Geezer came up with the idea of "pseudo-channel switching" on one of his HoSo56 amps:
http://www.el34world.com/Forum/index.php?topic=10999.0 (http://www.el34world.com/Forum/index.php?topic=10999.0)
You'd have two relays that switch simultaneously.
So here is what I am thinking ....................... for clean have things set like:
vol 3 trim 3 OD vol 5 FX level 8
then for the OD setting:
vol 7 trim 6 OD vol 5 FX level 4
I am sure these settings would need to be tweaked but that might be a starting place to have a clean tone for rhythm and a lead tone for
playing lead.
Don't know if you could breadboard this and/or how easy it would be to do ????
With respect, Tubenit
-
SILVERGUN,
You could check this idea out on your breadboard by simply experimenting with adjusting all the settings to see if you can get a reasonable clean tone first, ...................... and then ........................ adjust settings to see if you can get a good OD tone with nice sustain around the same volume or just slightly more volume for lead.
IF this works reasonably well, .............. could you record a rhythm and lead on clean and then the same song with OD settings for us to
hear?
With respect, Tubenit
-
That's kinda how I was thinking of approaching it.....except, I was picturing set value resistors across some of those same points...
So the resistors would be in parallel with the pots (volume, trim, etc...) and/or grid leak resistors for the clean tone...
And then you switch to your OD tone and it lifts a "shared ground" connection for a couple of the paralleled resistors......so that a couple points get switched in/out at the same moment, with one switch,,the same one we use for clean/od....but a 3PDT (if need be).... for guys who don't want to mess with relays :dontknow:
Is that worded well enough that you can picture what I'm suggesting?
Your idea with the pots would be a great way to determine what those resistor values need to be, and then the amp could be built without all of the extra pots....and I should be able to lay that out on the board without too much trouble.
Either way, I like the way you're thinkin' :thumbsup:
AND, I'm still kinda picturing this amp as a "pseudo" 3-channel....with CLEAN, OD, and SOLO (with the solo just being a different switchable "master" setting,,, that might also bring up the delay MIX :laugh:)
For right now,,,I'm still tweaking OD tone, and I need to take that as far as I can and then eliminate some of the gain to "create" the clean tone...
The front end drive of those first 2 gain stages has a lot to do with the OD tone that I really like......so somewhere along the way, I gave up any sign of a normal clean sound....because when I switch out the 5879 it's still a driven tone.
I hope this makes sense.....I wanted to get out some thoughts so you know where I'm coming from...
I'm starting to see the 5879 as more of the "icing on the cake" rather than the main gain stage (partially because of noise, but also partially because there are plenty of gain stages available to draw OD from.....it might take dropping (switching out) a cathode bypass cap on one of those stages to get back to a good clean sound :dontknow:
Just thinking out loud.... :icon_biggrin:
-
,,,I'm still tweaking OD tone
When I tried the 5879/CF bootstrapped OD, I didn't use it because of the clean to OD volume issue.
Having said that, I thought it sounded good BUT I also thought it could benefit from the OD tone control that I use on the original TBM and D'Mars. I thought the tone control added to OD might dial in "that" tone.
with respect, Tubenit
-
I also thought it could benefit from the OD tone control that I use on the original TBM and D'Mars. I thought the tone control added to OD might dial in "that" tone.
I saw that in one of your drawings.....haven't needed to try it yet, but I'll keep it in the holster
Here's a little drawing (from my idea above) of the proposed switching to knock down some of the gain in those first stages when you have the switch in the clean position...
- the added 500K across the volume pot drops that to a 250K pot
- the added cathode resistor cap combination drops the resistance, AND adds the cap for the OD tone
I think I have the switch drawn correctly for what I'm trying to accomplish... :dontknow:
I think this might help with the clean tone,, BUT, I think we would need another way of adjusting the 2 volumes in relation to one another
EDITED- fixed incorrect switch wiring
-
I think we would need another way of adjusting the 2 volumes in relation to one another
To me, that is the primary concern and issue.
With respect, Tubenit
-
To me, that is the primary concern and issue.
For me it's the amount of drive that the clean channel retained when I would switch out the 5879....it's definitely a see-saw effect of trying to find a good middle ground
Were you finding that the OD channel was much louder than the clean channel?....I have been able use the OD volume to balance the 2,,,but that is a compromise as well...
I'll just continue to try ALL of these things in an attempt to get it right.....it's not that far off
-
Using the "normal" 5879/CF that is not bootstrapped, I have no issue getting a great OD and clean at the same volume.
The bootstrapped version is so MUCH louder, that I could not find a good OD tone that balanced the clean tone volume.
In other words, the bootstrapped version has a GREAT OD tone but the "good tone" was so much louder then the clean. I could get an OD tone that matches the clean volume but it didn't sound good because the OD was so "reduced" in it's tone. Hope that makes sense.
With respect, Tubenit
-
The bootstrapped version is so MUCH louder, that I could not find a good OD tone that balanced the clean tone volume.
In other words, the bootstrapped version has a GREAT OD tone but the "good tone" was so much louder then the clean. I could get an OD tone that matches the clean volume but it didn't sound good because the OD was so "reduced" in it's tone. Hope that makes sense.
Yes, and I agree....
The OD tone does sound best when the OD volume control is above 5, and it does create a "balance" issue
Are you running a cathode bypass cap on the 5879....removing that might help, and I've found that when bootstrapped I seem to get just as much "drive", with a little less volume,,,as compared to not-bootstrapped and using a cap
You know me (I like OD), and I seem to actually like the 5879 better without the bypass cap :dontknow:
-
I preferred the bootstapped CF approach to not have a cathode cap. It sounded smoother to me.
Tubenit
-
Gentlman I may be wrong but I thought in a differant thread Slucky talked about using a voltage devider to pad down a signal to better match the loudness of two channels coming together. In other words dropping a bit of the signal from the OD section to better match the signal from the clean section.
I tried to find the conversation to referance from, but Im at work and dont have my saved files to pull from.
Maybe we can get some off those guys to chime in .I might be totally off base and it wasnt him but I thought it was.
I read from so many places trying to learn I get them mixed up sometimes. But If we can find away to drop some of the signal without changing the treble and bass characteristics, that might be the way to go.
Bill
-
But If we can find away to drop some of the signal without changing the treble and bass characteristics, that might be the way to go.
Please don't hesitate to chime in....the challange here is that the clean signal is one volume and then we are just adding the 5879 to that signal to make the OD tone, so inherently, the OD channel is going to be louder than just the clean channel.....
I am still thinking of a work-around, BUT I'm also still trying to get the OD tone just right,,,,so it doesn't make sense for me to try to balance a volume that isn't set in stone yet....and I may eventually choose to just use this circuit as a single channel amp, without worrying about the clean tone. I would like to see it be a balanced 2 channel amp, but I can't wrap my head around how to make it happen.
I'm so far off base that MY last idea was going to make the clean volume even lower, by reducing the gain to try to get to clean tone "right". :l2:
I'm thinking that T's original design is the best balanced version of this amp.
-
Im really interested in this also because I love the sound of the 5879 overdrive in this circuit Ive built the very 1st version of this and loved the sound of it.
I even went on to use the clean channel at the time which wasnt all that clean with the fat 3 gain stage version as a lead channel in a blues amp. I loved the sustain and blooming that one had in the clean channel.
But the high gain guys have to contend with this but they pad the signal by dropping some to ground with voltage dividers between stages.
Ive read discussions, but I still dont understand how that works or for that matter havnt been shown a clear example of how to apply it to a design.
Ive asked the question several times but I get a vague answer without a visual schematic to show me an example .
Sadly thats what I need to understand these things Im a visual guy.
Give me one example of how something fits in a circuit and why, and Im good to go. When I get home I will look through a bunch of my high gain schematics and see if I can find a common padding scheme between the high gain channels and the clean channels. At least maybe I can find a few examples post them and the really knowledgable guys here can explain them. Might be helpful might not
Thanks Bill
-
SG, did you build your version with all the OD pots? There are three - OD Trim, OD Drive and OD Volume. I thought the idea was to set the trim and drive then use the volume to match the level with the clean. Then again, I only played the amp at modest bedroom levels, so I never had a chance to crank it up, so perhaps the OD characteristic changes and requires re-adjustment of all the settings, which would be a pain for live situations.
-
Great job boys, I built the bogner XTC and having multiple channels the job of keeping then at similar levels I guess was a bit of a problem for the designers. The three stage CLEAN channel is one way to up the volume to match the OD.
Looking at REPLY #59 I guess you could use that schem and add a extra two triodes between the volume and level pots.
-
the high gain guys have to contend with this but they pad the signal by dropping some to ground with voltage dividers between stages
You don't need voltage dividers in this design. You have a volume, OD trim, OD volume, FX send, FX level. Essentially you have 5 volume pots to control gain stages. IMO, I'd rather have that then fixed voltage dividers.
I typically will use a voltage divider (like you see between the FX send and FX return) when I don't have room for a pot on the front of the chassis ............ OR it's an area that I never adjust the volume anyway.
With the 5879/CF bootstrapped, I still think the answer is Geezer's "pseudo-channel switching" in order to get a volume balanced clean to OD.
It would take about 5 minutes to figure out if this idea would work by setting the volume pot at 3 with FX level at 7 ............ & then change it to volume at 6 and FX level at 3. How does the OD sound like that? Is the volume between clean and OD balanced? Switching two DPDT relays at the same time would allow one to create 4 volume pot changes simultaneously.
With respect, Tubenit
-
Great responses GUYS,,,I really appreciate the attention and the desire to help :thumbsup:
SG, did you build your version with all the OD pots? There are three - OD Trim, OD Drive and OD Volume. I thought the idea was to set the trim and drive then use the volume to match the level with the clean. Then again, I only played the amp at modest bedroom levels, so I never had a chance to crank it up, so perhaps the OD characteristic changes and requires re-adjustment of all the settings, which would be a pain for live situations.
No jaz,,mines only got the TRIM and VOL.....I built it pretty similar to the first posted schematic on this thread, except I used a tube for the cathode follower....
The big problem with ME is....I like it better when they are all turned up,,,and that's how I've created this problem for myself
By using the lower wattage 6K6's and choking down the PI with the 10K shared cath. resistor, you can push all of those controls up to about 8 (including the MASTER) and still be able to sit in front of it :icon_biggrin:.....and that's where it really sings and sounds the best to me
BUT, at no point did I take the clean sound into consideration as I was just trying to max-out the OD tone
Looking at REPLY #59 I guess you could use that schem and add a extra two triodes between the volume and level pots.
REPLY #59 is THE BEST ANSWER....at least for me...I stayed last night and played around with it with good results....see below
:icon_biggrin:
-
With the 5879/CF bootstrapped, I still think the answer is Geezer's "pseudo-channel switching" in order to get a volume balanced clean to OD.
It would take about 5 minutes to figure out if this idea would work by setting the volume pot at 3 with FX level at 7 ............ & then change it to volume at 6 and FX level at 3. How does the OD sound like that? Is the volume between clean and OD balanced? Switching two DPDT relays at the same time would allow one to create 4 volume pot changes simultaneously.
YES!...that's it...read on
First,,,T, I apologize for any aggravation that I may cause by taking your nicely designed amp, and brutalizing it....I have just enough knowledge to be dangerous :icon_biggrin:....
Keep in mind that ---until yesterday I hadn't given the clean tone ANY attention at all and was just pushing the OD tone, thinking that I could always just go back and drop some gain and have a decent clean ....bad idea :embarrassed:...but this is MY first 2 channel amp build
I stayed a while last night and tried to test Geezer's approach and it works exactly as you think it would.....it seems to be the only way to have ultimate control over both tones and their volumes...
So I'm gonna go back to what I was doing and continue tweaking,,,knowing that I will be able to get back to clean by using the method outlined in REPLY #59
I think it'll be time to create a different thread, so that I don't muddy the waters surrounding T's original design, any more than I already have :icon_biggrin:
-
Hey man, I love it that you take a design posted and approach it in a fresh way to make it something innovative and your own. I am fully supportive of that and have zero aggravation around that. It's a good thing!
I think it's totally legit to just have a fully driven OD tone amp with no clean or a 2 channel amp that is moderate OD and then totally to max OD. It's all appropriate and good in my book.
I really like the OD tone you got. It's excellent! No reason to change it.
I'm just curious whether you can keep the uncompromised OD tone .......AND dial in some clean (or somewhat cleaner) at a comparable volume. That's where Geezer's psuedo channel switching idea got brought in.
Feel free to continue in this thread or start another. However you want to handle it is fine. I like watching the evolution of these design ideas unfolding. I'll keep watching what you do with this with interest.
With respect, Tubenit
-
Hey man, I love it that you take a design posted and approach it in a fresh way to make it something innovative and your own. I am fully supportive of that and have zero aggravation around that. It's a good thing!
Thank you sir....I truly value your support and direction...
I have one MAJOR mistake to report:
-In my last schematic (with parallel FX mod), I had eliminated the FX send pot and opted for a fixed value of 10K in place of that pot...
Well, that value is way too low, and I had come up with it while tweaking the OD tone with everything cranked....with the amp set like that, 10K is OK because there is a huge signal there and 10K knocked it down real good.....
BUT, when you switch it to clean, there is not enough signal to push past that 10K and most of the clean sound was going to ground and I was left with a very thin, anemic clean tone,,,if I left that 10K in there
- I switched it out for a 33K to simultate a setting of 3 on a send pot, and that appears to be a much better solution
-
Here's a small update...
I've spent a lot of time recently, tweaking and tearing the circuit down to learn more about what makes it tick....only to back track and return the circuit closer to the original design :undecided:
It seems like I have changed every other value in the amp, only to revert back to where it was... :icon_biggrin:
BUT, I spent a lot of time tweaking the effects return stage and the PI....because I thought it would make sense to push more current, by changing the bias point of the return stage.......
Well, by using the load line plotter, I determined that a more ideal operating point for the 12AU7 would be 33K plate load, with a 1.8K cath. resistor...
But in reality, I found that the increased current came with increased noise, AND I seemed to be hitting the grid of the 12AT7 PI too hard (causing hiss, and then cutoff, at a higher FX return "Master" setting)
So I spent a lot of time trying to push the boundaries of that area, and wound up with the 100K plate back in there, BUT, I increased the cath. resistor to 4.7K.......AND, I also took away the cath. bypass cap, and that provided a nice reduction in overall noise, and lowered gain (which I really liked there)
I tried it with and without that bypass cap, and it didn't seem to affect the sustain/harmonic blooming
I think that this change is very notable, and might be something that T (or anyone else) would want to try......by lowering the gain in that stage it has enabled me to drive the 5879 harder but with less amplification of the resulting noise :thumbsup:
And that's what I'm suggesting,,,,lose the bypass cap, increase the cath. resistor, and drop the gain in the effects return stage of the 12AU7, so that you can drive the 5879 harder AND raise the OD volume pot, for more singing sustain, with possibly less noise...
Of all of the moves that I have made, this one seems to be the most beneficial to my ears, for getting a "better" OD tone
It seems to have taken away some of the "boxy" gain sound that I thought I was hearing initially..... :dontknow:
-
Hey man, thanks for the update and the tweaking info. I'll probably try that in the next several weeks and report back how I like it.
With respect, Tubenit
-
I've been keeping up with the FX loop threads for the most part. following with interest.
One thing I'd want to do in such a circuit would be to install a switch to remove the entire set of triodes and all their circuitry from the signal path when FX loop not in use.
I sometimes use switched cliff style stereo jacks making use of the "ring" portion of the jack to do something -or not-, depending on its use. With such a switched stereo jack, when you insert a mono plug, the "ring" shorts to the "sleeve", which of course, is grounded. When you remove the plug, the sleeve is no longer grounded.
When this thread's parallel idea came up, the following occurred to me:
(http://i.imgur.com/I5MxARp.png)
values are generic. they aren't meant to rework what you've done here.
the focus is on R1 and R2 together, and the Return jack's switched connections.
Regarding the Return jack:
when loop not in use: (1) the "tip" is shorted to ground, and thus V1's grid is grounded. (2) the "ring" is open, not switched to anything; so this means R1 and R2 are in series. Signal at the Input travels directly to Output, bypassing the triodes and all its circuitry. R1+R2 & R11 form mix resistors, so the signal is attenuated (in these case of the values, 50%).
when loop in use: the junction of R1 and R2 is grounded by means of a mono plug in a stereo jack. Input would travel through the FX loop circuitry. ( and not through R1+R2, of course). R11 and R2 form a voltage divider, so signal is attenuated (in the case of these values, 33%). The Mu of V1 is a possible tweak point as is R11 and R2, of course.
I set R1+R2=R11 thinking in terms of a single channel AB763, where in absence of the 220K mix resistors, one might want to attenuate the signal by 50% like a 2 channel AB763. but, R1 and R2 don't have to be equal, and they could be bigger I suppose, like 1M each.
The Mu of V1, plus R11, R3, and R4 in addition to R1 and R2 would all be juggled to maintain similar signal levels for in use and not in use FX loop modes...
if all of this should be another thread, I'm happy to spin it off. Or if, there is no interest, I'm prepared for that as well! (tho I'd certainly like to hear comments on the idea...)
-
One thing I'd want to do in such a circuit would be to install a switch to remove the entire set of triodes and all their circuitry from the signal path when FX loop not in use.
I think you have a good idea with the cliff jack's shorting to ground. I think that would work?
I used to use a simple mini-toggle DPDT but found that I always have the FX on since one of the main uses for me is to use the FX level pot as a master volume which works excellent in that regard, IMO. So, I personally don't want the FX switched in and out. I would just switch the pedal into bypass mode instead. Just a personal preference.
with respect, Tubenit
-
One thing I'd want to do in such a circuit would be to install a switch to remove the entire set of triodes and all their circuitry from the signal path when FX loop not in use.
You're good on this thread term... we like ideas ...although this has the potential to spin-off to another thread...
I like this one,,,and was eventually going to try something like this as a way to switch an EQ in and out in the loop, as a solo boost, lead tone..
I don't need the loop to be active all the time,,,and it might be cool to just put a delay and an EQ there and be able to switch to those being activated, and just leave the pedals on all the time (and sitting on top of the amp) :dontknow:...
And I guess we "could" take the FX level pot out of the loop wiring (along the lines of your diagram), and just make it a true Master.
So for someone like me who wants to add the boost, along with the loop, we would use less attenuation when the loop is switched in,,,,at which point it becomes more of a "boost loop" than a fixed level effects loop
Just thinking out loud..............
-
I have a question about the preferred components that are used for these builds. As an example of what I have on hand, I have an abundance of carbon comp resistors, that I use for repair as like-in-kind on old repairs. I've used the same in scratch-build experiments. For capacitors, I stay with modern, of like value (or close).
Eventually, I want to include this information on my BOM's, as well as sources with part numbers. I use a spreadsheet for easy copy/paste, and then print the same as a PDF sheet with the drawings. The beauty of this is that this database can exist independent of any drawing. I already have something of a database started, but not in the format that I want to build for this. But, I can transfer most as I need.
Anyway, it would be good to include the best with comments as to reason for use, in my database. Please comment with your preferred choices, and any reason why you like them. Thanks for all help.
Jack
-
If you are ordering parts from Hoffman than I would recommend Orange Drop caps in the clean and LTPI to power amp.
I'd use Xicon in the OD section and perhaps the FX also. You could use Mallory 150s if you wanted in the OD and FX.
I typically use metal film resistors but I don't see why carbon comp wouldn't work? The CC's may be a little noisier at idle?
With respect, Tubenit
-
If you are ordering parts from Hoffman than I would recommend Orange Drop caps in the clean and LTPI to power amp.
I'd use Xicon in the OD section and perhaps the FX also. You could use Mallory 150s if you wanted in the OD and FX.
I typically use metal film resistors but I don't see why carbon comp wouldn't work? The CC's may be a little noisier at idle?
With respect, Tubenit
That's the info I want to document. And yes, Hoffman will go in as a primary source for these builds.
I agree with the noisy CC resistors. I don't mind this in some old amps. However, the '63 B-12-N is my standard for quiet. And, there are no CC's in that one, other than the PS. All the more reason to use proven components.
I'll follow your lead on the placement of the componets that you've given. And, hope that others will express their preferences, as well. Thanks a lot.
Jack
-
Jack,
I always use metal film resistors, just because of the low noise quality...
I trust T's ears more than my own when it comes down to choosing components....
I try not to get too caught up in chasing "mojo" by using certain brands of components,,,,and if anything, I'll try an oddball cap here and there just to spice things up....
On one build I noticed that it sounded "better" if I used 2 caps in parallel to achieve the correct value....as if I was getting the tonal personality of each cap and they complimented each other....
here's the thread:
http://www.el34world.com/Forum/index.php?topic=16281.msg159408;topicseen#msg159408 (http://www.el34world.com/Forum/index.php?topic=16281.msg159408;topicseen#msg159408)
And if I was going to build this amp, I would just follow T's layout, and component choices, because you just can't argue with the success of his builds......Although I might try a parallel cap or 2 :icon_biggrin:
-
I would just follow T's layout, and component choices, because you just can't argue with the success of his builds.
I easily trust the tone of my amps can be improved upon. And it's mostly subjective regarding tone and personal preference. I think what I have done is a reasonably starting point with the understanding these amps are intended to be tweaked for personal taste.
I hope forum members will continue to experiment and mod the amp designs Geezer and I have done and report back what has worked, what has improved and what doesn't work.
The collaborative efforts continue to help everyone's tone.
With respect, Tubenit