Gibson EH-185

[pompeiisneaks]

Oh thanks!  I'll check that out.  Yeah I've realized that, now that I have the actual resistors in hand, they'll be going off the side (the two 1.5k have screw holes so I can mount them to the chassis for heat dissipation.) The other big 20k I'll mount to the B node capacitor and have it sitting a good half an inch above it for room to breathe.  Oh sheesh, the jacks should be like my vox AC30 for the dual jack setup right?  Sorry I'll fix that too.  I'll upload an updated one later. 

I'll have to play with the visio shapes for schematics too, thanks.

~Phil

[pompeiisneaks]

I think this is right for the jacks... I've moved the 20k 20W resistor to page 2 with the caps, and moved the 1.5k off the board near it for reference.

Does that look good?

Edit: latest schematic and layout are in the first post.

~Phil

[sluckey]

Input jacks still wrong.

[pompeiisneaks]

Oh yeah I see, d'oh!  Here's try three? :)

Edit: latest schematic and layout are in the first post.

~Phil

[sluckey]

Strike three! You have the middle jack tip strapped directly to ground.

[pompeiisneaks]

GAH!!!! lol okay this is right now, (Or at least I hope, if not, I need to drink more this st paddy's day and just give up for 24 hrs lol)

Edit: latest schematic and layout are in the first post.

~Phil

[sluckey]

Nope. The attached layout matches your schematic. Be aware that your schematic will result in only 1/2 of the instrument signal reaching the volume pot. You can snip the jumper between the ground lug and switch lug on both jacks to deliver all the instrument signal to the volume pot. The original schematic does not use a switching jack.

If you prefer to have a typical HI/LO jack input like a typical Fender, look at Doug's Library of Information.

[pompeiisneaks]

Trying again...

Thanks Steve, sorry I'm getting it now, I was trying to do the fender jacks, but even that wasn't quite right because I don't have the 1M to ground.  I'd rather stick with the schematic, I want to see what it sounded like as best I can.

Edit: latest schematic and layout are in the first post.

~Phil

[sluckey]

I'd rather stick with the schematic, I want to see what it sounded like as best I can.

Then remove the jumper between the ground lug and switch lug on both jacks or use Switchcraft 11 jacks.

[sluckey]

There's a discussion about this amp over at TAG that you may find interesting or make some contacts for additional info...

     http://ampgarage.com/forum/viewtopic.php?t=29052

[pompeiisneaks]

Thanks, gotcha, so the big issue is that I'm using a drawing of a 12A switchcraft type instead of 11.  On the 11 there's no 's' switch post.  I'll update that. (I'm at work now, I'll get it later).  Sadly I can't load that link I get a security warning that the site has malware in chrome.  I'd rather not risk it at work, I can load it from a Linux host later maybe? 

~Phil

[DummyLoad]

There's a discussion about this amp over at TAG that you may find interesting or make some contacts for additional info...

     http://ampgarage.com/forum/viewtopic.php?t=29052

that site's been blacklisted as a malware source.


--pete

[pompeiisneaks]

So I've removed the link from ground to switch.  Here we go.

Edit: latest schematic and layout are in the first post.

~Phil

[sluckey]

The resistor that connects to the 6L6 cathodes should be 10 watts.

[pompeiisneaks]

Oh, I knew that and ordered one, but your'e right, the actual resistor on the diagram looks like a normal 1watt or less type.  Fixed, thanks :)

Edit: latest schematic and layout are in the first post.

~Phil

[sluckey]

Just a suggestion... rather than posting a new layout in every reply and ending up with dozens of layouts scattered across multiple pages, just post a single layout in the first message and replace it with the most current revision. Then we will never get confused about which layout to use and the forum server will remain clean and lean.

[pompeiisneaks]

Oh excellent idea, I should have thought of that

Edit: and done :)

~Phil

[kagliostro]

Just a council, if you use trasparency (near 20% will be OK) on the board, the route of the wires that are under the board is readable

and so is easier to read the layout

Franco

[pompeiisneaks]

Oh very cool, thanks!

~Phil

[sluckey]

There's a discussion about this amp over at TAG that you may find interesting or make some contacts for additional info...

     http://ampgarage.com/forum/viewtopic.php?t=29052

that site's been blacklisted as a malware source.


--pete

Guys, I would never post a link to a malicious website. TAG has been on Google's warning list since June of 2015 when they were hacked. The site admin removed the malicious code but for unknown reasons has not coordinated with Google to be removed from the list. That's a shame. Traffic is way down on TAG because of the Google warning.

I'm not advocating ignore Google warnings. Just saying that TAG is safe, There is no danger on the TAG site.

[pompeiisneaks]

I don't disagree, or doubt you, but I was attempting to follow that link from work (and I am at work again) and they're going to not be happy if I even try.  Once home, and if I can remember to look it up, I will. 

Thanks for the information, it is sad that they can't be bothered to work with google to get the all clear.

~Phil

[sluckey]

I have some 3K CC resistors if you are interested.

[pompeiisneaks]

OO I may be, I'd love to keep this closer to stock, everything now is only 3.3k,  I'll pm.

~Phil

[pompeiisneaks]

I have some 3K CC resistors if you are interested.

Got them today, Steve, thanks so much
Phil

[pompeiisneaks]

Okay,

Amp is all built and works great, but I've got the instrument jacks wired wrong obviously because only the 'mic' input works.   I got switchcrafth 11 type jacks since you said that jumpering the two S to G is not needed.  I thought I read that 11 would work in my case, but I may have done that wrong.  Here's what goes on.

If I measure tip of either to the other end where it connects to the pot, it reads 100k just like it should, if I connect tip to tip I get 200k like that should.  I get no continuity to ground on either tip connection.  I plug a sine into either and I can see it going down the wire TO the resistor, but on the other side of the resistor, its completely gone. 

If I input into say instrument 1, and then jumper from instrument 2 to mic, it works. 

What am I doing wrong? 

I'll go get a pic of it too, to see if that helps.

Edit:  Pics: https://goo.gl/photos/uLDupe6vkZehhWyt6

~Phil

[pompeiisneaks]

NVM, found it, nothing to do with the jacks.  It was the connection of the output from the volume pot to the input of the grid that somehow was touching the pot and grounding out.  I desoldered it and the ground loop disappeared, resoldered it and it was fine, so it was just that.

I'll have a video up probably tomorrow night with the actual build details and final output of the amp.  Sounds quite cool, except that the 'mic' input is way sensitive, I can't get it much over maybe 3 or 4 before it starts overdriving quite a bit, and getting it to like 7 makes the distortion sound horrible ;) 

The instrument jacks get a bit distorted/od at about 7 or 8 but still really sound good.

~Phil

[sluckey]

Your layout shows a 1K resistor connected to pin 6 of V2 and V3. Your schematic shows 100K which is correct. What did you actually put on the board?

[pompeiisneaks]

It's 100k, thanks for catching that on the layout, I'll fix it. 

Something else kinda weird.  I get no output for a while, sometimes only, and if I start probing around with my oscilloscope probe, it suddenly outputs sound and starts working.  Why would it be silent until i do something like that? 

I think it turns on every time I probe the output of the capacitor that is going into the treble pot...  Makes no sense.  Other times when I turn it on, it just works.  Last time it was dead silent for almost a minute until I grabbed the scope probe and touched it and then boom, sound.

~Phil

[sluckey]

Bad connection comes to mind.

[mresistor]

--pete

Guys, I would never post a link to a malicious website. TAG has been on Google's warning list since June of 2015 when they were hacked. The site admin removed the malicious code but for unknown reasons has not coordinated with Google to be removed from the list. That's a shame. Traffic is way down on TAG because of the Google warning.

I'm not advocating ignore Google warnings. Just saying that TAG is safe, There is no danger on the TAG site.

Absolutely true.  I got that malware warning and then decided to investigate and can confirm what he says is true, The site is clean and no problems for me for quite a while now. 

[pompeiisneaks]

Bad connection comes to mind.

It is possible, but where would it be?  works perfectly from there on out. 

I have one other thing I noted that may be related... the way the phase of the two inputs works seems like they're out of phase.  If I input the guitar into one of the two instrument inputs and then jumper the other over to the mic input, the volumes are decreased some, until you get the mic level high enough.  Also, though, when I connect the scope probe to one or the other side of the PI, they seem opposite of one another if I just do one or the other.  Seems odd, though, because the mic has two tubes which should mean its back in phase by the time it outputs at the second tube right?   

~Phil

[sluckey]

If you want to compare phase relationships of the signal as it passes through the amp you'll have to trigger the scope from the same source. Don't set the scope to trigger on the same signal you are looking at. IOW, if you are injecting a signal from a generator, then externally trigger your scope with that signal. Or, if you have a dual trace scope, connect the sig gen to channel two and trigger the scope on channel 2. Then use channel 1 to check the signal as it passes through the amp. You'll be able to see every phase inversion this way.

[pompeiisneaks]

Yeah I have a 4 channel scope, and I was using inputs 1 and 2.  1 is the input signal, and 2 I was putting at the PI on one side.  If the volume was at max on the instrument input but 0 on the Mic it was in phase with the input, but if I raised the volume of the mic, it lowered the volume for a bit until the mic input seems to overpower it and then the phase is reversed. 

Or so it seems to me anyway.  If I put instrument at 0 and mic up a bit, the phase is def reversed.  I'm not sure why, when the mic goes through two tubes but the input only goes through one. 

Oh wait...

That makes sense after all.  The mic input is in phase when it enters the PI  but the instrument is opposite phase as it has only gone through one stage.   so I guess it means I need to not jumper them.  The mic input is probably just too hot for a guitar at this point, maybe I need to put a 68k or 33k inline on that as well?   Then I'd want to use either the one or the other at that point.

~Phil

[sluckey]

That makes sense after all.  The mic input is in phase when it enters the PI  but the instrument is opposite phase as it has only gone through one stage.   so I guess it means I need to not jumper them.

Ah, now I understand. You're correct. When you jumper the instrument input to the mic input the signals will be opposite phase when they are recombined at the common plates of V2 and V3 and will cancel. Since the mic path has more gain, that signal will tend to swamp the instrument signal.

Since the mic channel is too hot for guitar, you could use a split load on the plate of V1. IE, replace the 100K plate resistor with two series 47K resistors and connect the coupling cap to the junction of the two resistors rather than directly to the plate. The two resistors don't have to be the same value but their total resistance should be close to 100K.

[pompeiisneaks]

Sounds like a good idea.  I'll give that a try.

[pompeiisneaks]

I did it, (I only had a 47 and 55k around but I figure its pretty close).  That seems to have tamed it a bit, would it also be good to put a resistor inline between the input jack and the grid like on all others I've used?  Attenuate it a tad? 

Also, I still can't find the source of that odd behavior.  I'm going to attach a image of the board and circle in red (with arrows pointing to them if they're not obvious :D ) showing the locations I can touch that seem to 'kickstart' the circuit.  If I probe anywhere else, it stays silent.  I've reflowed all the connections in the area. 

One other oddity, I found.  After the circuit is 'up' the areas near the blue output wires to the 6l6's have continuity to ground.  But ONLY after that, before it happens there's nothing.  IS that supposed to happen?  (Doesn't seem right)

One final question...

I looked up the 6l6 datasheet and the grid and anode voltages are supposed to be different for a self(cathode) biased amp, but in this amp they're not.  Both sit at 278 V. 

I checked the cathode voltage at the 250 (245 measured) resistor and I get 25.5 V idle, which at 235 ohms gives me 104 mA which seems to be okay, but I'm not sure that's a perfect comparison since the datasheet is for a 400V Anode, 300V screen.  (or 400V anode 250V screen).   Or is that all fine?  Doesn't seem like its having too much issues on the power amp sid.

It seems like something between my preamp section and the PI is 'stuck' and gets a kick in the pants if I touch any of the red circled areas shown above, and then starts outputting to the Power Amp side.

~Phil

[pompeiisneaks]

BTW, Here are some voltages.  The first set is pre 'kickstart' when there is no output.  The second set will be post. 
(V1-V3 preamps, V4, PI, V5/V6 6l6's
Before:

V1: Pin 2, 12.8mV, Pin 3 1.09V, Pin 6 138V
V2: Pin 2, 120mV, Pin 3 .77v, Pin 6 94.3V
V3: Pin 2, 94.3 mV, Pin 3 .7V Pin 6 94.3V
V4: Pin 3 279V, Pin 6 107V, pin 8 1.96V,
V5: Pin 3 311V Pin 4 313V Pin 5 35mV Pin 8 25.5v
V6: Pin 3 311V Pin 4 314V Pin 5 53mV Pin 8 25.5v

Then after:

V1: pin 2 13.9 mV Pin 3 1.0v Pin 6 125V
V2: pin 2 25 mV Pin 3 .7v Pin 6 85V
V3: pin 2? Pin 3 .7v Pin 6 85V
V4: pin 3 148V Pin 4? Pin 6 118V pin 8 2.5v
V5: Pin 3 290V Pin 4 293V Pin 5 50mV Pin 8 30V
V6: Pin 3 287V Pin 4 292V Pin 5?  Pin 8 30V

the ? are all low mV ranges that kept coming and going so I didn't feel confident calling it 300mV no 10 no 0 no 30 no .... (if you get the idea, it was almost like a cap discharging and then charging).

The B+ reads:

A 408V
B 313V
C 271V
D 164V

Now maybe this is just somethig I'm not getting, but why is the second anode of the PI only at 107 V on the exact same rail as the other which is then at 279V?  They almost balance out when it's 'running' (148 Vs 118)

Also I noted as I put my Voltage meter on the treble pot, input side, the voltage was negative about (Edit, this was actually wrong:-20V it's actually about -170 when I first hit it, and then it drops fast) but slowly went down to a point where it 'turned on' maybe -2 v or so?  Does that mean something is pulling the voltage negative there that shouldn't be and is causing this imbalance, and until it gets nearer to ground potential, it won't output?  It seems the problem is the PI or something leading into or out of it?

~Phil

[pompeiisneaks]

Figured it out!!!

Layout error :)

ON the schematic, the output of the treble ties into the output of the 750 pF cap, then THAT goes to the grid of the first side of the PI.  I was skipping it entirely and going from output of treble straight into the grid, skipping the 750 pF completely.  I've fixed it, and it's working! :)

~Phil

[pompeiisneaks]

Okay so after a bit of playing with it, I do have something odd going on.  I think it is an oscillation issue.  I have the instrument inputs at low volume and they sound great, when I get up to maybe 7 or so, it starts in with a high pitched squeal/whistle.  The Mic channel seems fine at first too but sometimes ends up with an insane amount of hum buzz at times as well, but it also is intermittent.  Is this a ground loop issue, or something else seriously wrong?   Could it be interaction between the two channels after the mods I made to make the mic input a bit more calm? 

~Phil

[sluckey]

At this point it could be one or more of several things, layout, bad connection, wiring error, tubes, etc. Show us some pics. Your backward chassis layout could be a major factor. I would pull V1 and V2 and concentrate on getting the instrument channel right first.

I doubt the V1 plate resistor mod is a factor if you did it logically and neatly.

[pompeiisneaks]

Ok thanks,

I'll try that and get pics.  I think I did try that and I had clean tone completely at that point, but now I don't remember (I really need to write notes as I troubleshoot, it would make things a lot easier for me later heh).  I can also try just the mic input and remove that V3 and see what taht gives as well.

~Phil

[pompeiisneaks]

Here are some pics. 

I've had some serious issues troubleshooting because it got significantly worse.  I started tapping around with the chopstick but the sound was so loud I could only handle it in short bursts.  Then I found that when I touched the grid input from one of the tubes it went either way worse.  I traced that back to the pot and touched the pot and it disappeared and it was working fine.  I touched that center pole on the pot again and it would go nuts.  I pried it a touch and it seems to have stopped completely.  Does that mean the pot is bad, or do I just likely ahve a bad solder joint there?  it seems okay for now.  The mic input also has a decent amount of buzz/hum, maybe the ground on that stage is a bit weak?  The other two inputs seem really clean if I just turn the mic input down to 0. 

Here are the pics of the guts:

https://goo.gl/photos/REerjstcWZ88ySXq5

~Phil

[sluckey]

Sounds like a bad pot or a bad connection on the vol pot wiper or ground terminals. V3 grid relies on a good path to ground through the vol pot. Touch up all solder joints and spray clean the pot. Use electronics spray such as Caig Deoxit. Don't use WD-40.

I thought you were going to pull V1 and V2 until the instrument channel is fixed??? Doing so will prevent the mic channel from being a factor in the instrument channel problems. Once the instrument channel is working well, then plug in V1 and V2. Any problems that crop up should then be associated with the mic channel only. If you are satisfied that the instrument channel is working as expected, then ignore this paragraph.

You need to use a switching jack for the mic input and it needs to be wired IAW the original schematic. This will help keep the high gain mic input quiet when nothing is plugged in. The mic input jack on your *.sch schematic is drawn wrong.

Your pics are very good. But, we need at least one high rez pic that shows the ENTIRE completed chassis wiring. The pics you posted don't even have the rectifier tube socket connected.

[pompeiisneaks]

Thought I explained that, sorry.  I did that and got the instrument nice and clean before I found this.  Sorry I had swapped the left power tube location with the rectifier and the noise was worth.  I'll get some now that I reconnected it all up.

How can you tell a switched input from a non switched input on a schematic?

Phil

[sluckey]

I'm still confused. Are you saying the instrument channel is fixed and the only problem you have is the mic channel?

A switch jack has a circuit symbol that is different from a non-switched jack. This pic shows Switchcraft 'type 12A' switched and 'type 11' non-switched jacks.

[pompeiisneaks]

Oh gotcha, I see that now, so I do need to get a switched one for the mic input.  Okay.  I'll have to swap that out. 

Second thing, though, is that I did it again today where I have just the V3 in and I can get intermittent good performance out of it.  If you look at the same link I've added photos from today and put them to the front.  (With the system working).  https://goo.gl/photos/REerjstcWZ88ySXq5

I'm also going to attach a link to an audio sample I took of it:  https://www.dropbox.com/s/hc8ql1qwexplneh/guitarEdit.mp3?dl=0  If you listen at the first, you can hear a bit of 'buzzing' in the sound, but if the volume is low (which I do for a bit after that), it's very clean.  Then I turn it back up and it starts buzzing, snapping, popping etc, and there's a very high pitched almost inaudible squeal going on. 

I also Still have this weird issue where the center post of the volume pot for the instrument input, no matter how many times I try to resolder it etc, seems to go berserk until I push it to just the right position, and then it goes mostly clean like this except for the high whistle/squeal at high volume.  When it was freaking out, I get a huge hum and something akin to radio freq noise.  If I move the anode wires and ground wires around it changes the pitch etc, which leads me to think this is oscillation caused b y the wiring.  (The mic input seems to not have this issue, just a heavy grounding noise when I have the volume up, but maybe because its amplifiying it so much more than the instrument input.  When I was playing with the scope, I got maybe 20V output from the instrument at max volume, but the mic gets probably 4x that after we dropped it down with the split anode load and I added a 100k resistor in series on the input. 

Let me know what you think of the pics and of the sound.

~Phil

[sluckey]

Replace the vol pot. If you don't have a spare, steal the pot from the mic channel. I really couldn't tell much from the sound sample using my cheap computer speakers.

I do have a concern about your pics. Your speaker jack sits right above your mic preamp tube. That's the worst possible place for the speaker jack. Unscrew the jack from the chassis and just let the jack dangle off the end of the chassis, far away from anything. And get that coil of OT extra leads far away from the input jacks too.
 

[pompeiisneaks]

Will do, I'll report back when complete.

Phil

[pompeiisneaks]

Okay did all of the above and it seemed better, but to test I put the output jack back where it was and it didn't change the sound/tone at all. 

I found there were definitely two culprits.

1. the pot is bad, it keeps going intermittently connected on the wiper.  It also seemed to make the weird high pitched noise.  When I replaced the pot with a spare one from the old Vox, it went way better but had a nasty hum, I kept messing with the ground a bit and got that to go too but I think if I probe the bus with a chop stick it still pops occasionally so somewhere else i need to fix a poor solder connection to ground. I know the pot was bad also because I had it out of the chassis and as I'd connect it to the wiper and either side it would go from reading fine to suddenly 0L (dead open, no conductivity) to like 3M or 4M etc, like only partially any connection was happening, and then if I'd put a little pressure on it, the resistance would come in until I released the pressure and then it would go back out again. 

2. I realized the bulk of the noise may ahve also come from my grounded wire from pot to the grid of the tube.  It was really doing weird things, so I just replaced it and bam, the rest of the problems went away. 

Thanks for the help!

~Phil

[pompeiisneaks]

Btw here's the view of it from the outside now:

https://goo.gl/photos/FhvWnswzuqDzLsuBA

You can see the hole for the missing pot and the temp pot sticking out on the bottom, I'll need to get a new pot, and I think I'll get isolating washers for the inputs and replace the mic input with the switched one as mentioned and she'll be done! ;)

~Phil