Please help! Signal bleed at zero volume - Classic 30

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FleshOnGear
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Please help! Signal bleed at zero volume - Classic 30

Post by FleshOnGear » Sat Apr 10, 2021 3:37 pm

Greetings! This is my first post here, and I’m hoping you guys can help. I just bought a used Classic 30. I’m not sure how old it is, but it’s not the second version. The amp sounds great, but I’m having a problem with it.

The amp passes signal even when the volume knobs are all the way off. The sound is the same regardless of which channel it’s on - a muffled clean tone sound. It’s only a problem in the overdrive channel, as it causes a mix between the overdriven tone and the rogue clean tone when the channel volume is turned up. Once the volume is up around maybe 4-5 you can’t discern the clean tone anymore, but then the amp is too loud for most home use.

I’ve done some testing on the amp, just stuff I can do without removing the PCB, using only a multimeter. All of the volume controls’ CCW terminals have continuity to ground. The cathode resistors and bypass caps of V1 A and B have continuity to ground. The caps at the preamp power supply nodes measure within tolerance according to my multimeter, but I don’t know if there could still be a problem the meter can’t detect. The amp doesn’t exhibit the usual signs of bad power supply caps.

I tried grounding out the output of V1A, and it reduces the signal bleed, but does not eliminate it. Grounding the grid of V1B actually makes the signal bleed louder. Plugging into the effect return eliminates the signal bleed. It seems like V1A is causing interference in V1B, but I don’t know how.

What else should I check? I’m just baffled. Thanks for reading.

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JamesPaul
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Re: Please help! Signal bleed at zero volume - Classic 30

Post by JamesPaul » Wed Apr 14, 2021 11:36 pm

Just to clarify, this only occurs when you are sending a signal into the input?
Enzo wrote:I find if the amp is working, that is a good point to stop fixing it.
James Paul's Peaveys
Decade, Classics, Ecoustic, Windsors, VYPYR, Triple XXX, XXL, VKs, Bandit, JSXs, VIP, Piranha and a Penta.

FleshOnGear
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Re: Please help! Signal bleed at zero volume - Classic 30

Post by FleshOnGear » Thu Apr 15, 2021 7:22 am

JamesPaul wrote:
Wed Apr 14, 2021 11:36 pm
Just to clarify, this only occurs when you are sending a signal into the input?
Right. And plugging anything into the effects return interrupts the signal.

I’ve discovered after a bit more tinkering that the amp only exhibits the signal at “zero” volume problem intermittently. When I power on the amp, it will randomly decide whether or not to behave normally, and it will stay in that state as long as the amp stays on. If the amp decides to bleed signal, I can turn the amp off, wait a few seconds, power it on again, and it might return to normal. Very strange.

rogue777
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Re: Please help! Signal bleed at zero volume - Classic 30

Post by rogue777 » Thu Apr 15, 2021 9:46 am

Not saying this will fix it,,,

I was wondering, focusing on the clean channel, does it make any difference if you swap tubes V1 with V2 and try it?
Last edited by rogue777 on Thu Apr 15, 2021 5:00 pm, edited 1 time in total.

FleshOnGear
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Re: Please help! Signal bleed at zero volume - Classic 30

Post by FleshOnGear » Thu Apr 15, 2021 12:30 pm

rogue777 wrote:
Thu Apr 15, 2021 9:46 am
Not saying this will fix it,,,

I was wondering, focusing on the clean channel, does it make any difference of you swap tubes V1 with V2 and try it?
I didn’t swap V1 and V2, but I did swap in a set of known-good 12AX7s. I’ll try swapping V1 and V2 just in case.

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JamesPaul
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Re: Please help! Signal bleed at zero volume - Classic 30

Post by JamesPaul » Thu Apr 15, 2021 10:49 pm

FleshOnGear wrote:
Thu Apr 15, 2021 7:22 am
JamesPaul wrote:
Wed Apr 14, 2021 11:36 pm
Just to clarify, this only occurs when you are sending a signal into the input?
Right. And plugging anything into the effects return interrupts the signal.

I’ve discovered after a bit more tinkering that the amp only exhibits the signal at “zero” volume problem intermittently. When I power on the amp, it will randomly decide whether or not to behave normally, and it will stay in that state as long as the amp stays on. If the amp decides to bleed signal, I can turn the amp off, wait a few seconds, power it on again, and it might return to normal. Very strange.
After it is powered on, does the Channel Select Switch have any effect on how it behaves?
Enzo wrote:I find if the amp is working, that is a good point to stop fixing it.
James Paul's Peaveys
Decade, Classics, Ecoustic, Windsors, VYPYR, Triple XXX, XXL, VKs, Bandit, JSXs, VIP, Piranha and a Penta.

FleshOnGear
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Re: Please help! Signal bleed at zero volume - Classic 30

Post by FleshOnGear » Fri Apr 16, 2021 10:00 am

JamesPaul wrote:
Thu Apr 15, 2021 10:49 pm
FleshOnGear wrote:
Thu Apr 15, 2021 7:22 am
JamesPaul wrote:
Wed Apr 14, 2021 11:36 pm
Just to clarify, this only occurs when you are sending a signal into the input?
Right. And plugging anything into the effects return interrupts the signal.

I’ve discovered after a bit more tinkering that the amp only exhibits the signal at “zero” volume problem intermittently. When I power on the amp, it will randomly decide whether or not to behave normally, and it will stay in that state as long as the amp stays on. If the amp decides to bleed signal, I can turn the amp off, wait a few seconds, power it on again, and it might return to normal. Very strange.
After it is powered on, does the Channel Select Switch have any effect on how it behaves?
No

FleshOnGear
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Re: Please help! Signal bleed at zero volume - Classic 30

Post by FleshOnGear » Sat Apr 17, 2021 6:56 pm

rogue777 wrote:
Thu Apr 15, 2021 9:46 am
Not saying this will fix it,,,

I was wondering, focusing on the clean channel, does it make any difference if you swap tubes V1 with V2 and try it?
I swapped V1 and V2. It helped. So I tried a bunch of my 12AX7 stash, and some tubes allowed signal bleed, others didn’t. Strange.

rogue777
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Re: Please help! Signal bleed at zero volume - Classic 30

Post by rogue777 » Sat Apr 17, 2021 7:23 pm

That is strange. I would of thought all the tubes would be the same.

Make sure the tube socket is clean itself, and the PC bd area is clean (no contamination resulting in leakage).
All the tube socket connections should be electrically isolated from each other.

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