Scratchy Guitar Volume Pot Problem

[matttornado]

Hello

I have this issue when I turn my guitar's volume up and down I get a scratchy sound from my amp.
When the guitar volume pot is not being turned, it seems fine. The problem seems to be when I turn the volume from 10 to 0 or 0 to 10 quicky. If that makes any sense. gradual turns of the guitar volume while playing does not make weird noises.

So far I tested an ruled out:
- The guitar - amp did the same thing with my other guitars. Guitars do not make the noise plugged into other amps.
- guitar cord. Only using one and tried a few others - no fix
- cleaned all jacks and sockets on amp - no fix
- checked all three preamp tubes with a known good one - no fix.
- checked all controls on the amp. No scratchy pots - no leaking DC, all amp controls work and sound as they should.
- cleaned all tube sockets

Next step is to open the amp up and poke around inside with a chopstick and try to make the noise happen.

I noticed that when I move the guitar cord's plug , at the amp's input, while plugged into the high treble input, it makes a scratchy sound while the other three inputs don't make a noise when doing this,

I also notice when I wiggle the PI tube, I get some some weird noises but they might be normal?

First thing I'm going to check are the inputs and check the solder joints for any broken or loose wires.

Then chopstick the rest of the amp and look for loose wires / bad solder joints.

Any other suggestions are welcome.

 

[fitz]

Deoxit.
In the pot(s).
In the jack(s).
In the tube socket(s).
Re-check for noise.

 

[Kutt]

What amp are we talking about here?

 

[Kutt]

This happens to me with my EVH 5150III 100w Stealth. Not sure if it's the same root cause, but if your amp is super high gain it may be a sensitivity issue more than an actual fault. If so you'll drive yourself nuts trying to pinpoint it.

They make low friction pots which allegedly cures this problem. I have not used them myself though.

 

[matttornado]

Deoxit.
In the pot(s).
In the jack(s).
In the tube socket(s).
Re-check for noise.

Did all of that. forgot to mention cleaned tube sockets.

 

[Pete Farrington]

The problem seems to be when I turn the volume from 10 to 0 or 0 to 10 quicky.

Is there an accompanying ’thump’?
Does it happen at all settings of the amp’s controls, especially channel volume, presence and treble?

 

[matttornado]

What amp are we talking about here?

1959 Superlead

 

[matttornado]

Is there an accompanying ’thump’?
Does it happen at all settings of the amp’s controls, especially channel volume, presence and treble?

No thump that I'm aware of . yes all level settings, both channels,

 

[matttornado]

This happens to me with my EVH 5150III 100w Stealth. Not sure if it's the same root cause, but if your amp is super high gain it may be a sensitivity issue more than an actual fault. If so you'll drive yourself nuts trying to pinpoint it.

They make low friction pots which allegedly cures this problem. I have not used them myself though.



View attachment 103564

This amp is not new to me. I been playing this amp for 27 years the same way and this never happend before. It's not high gain, just Superlead gain. Not the guitar's pot.

 

[Pete Farrington]

High value bright cap, eg 4n7?
As a temporary diagnostic measure, how about if one of its legs is lifted?
Or a 100pF anode to cathode cap fitted to the input stage.

 

[matttornado]

High value bright cap, eg 4n7?
As a temporary diagnostic measure, how about if one of its legs is lifted?
Or a 100pF anode to cathode cap fitted to the input stage.

the bright cap on my volume 1 pot was removed many years ago.
I can try a 100pF cap on V1.

 

[Spanngitter]

So far I tested an ruled out:
- The guitar - amp did the same thing with my other guitars. Guitars do not make the noise plugged into other amps.

If all guitars show a scratchy pot on this amp but not on other amps the problem is not the pot, it is in most cases DC on the signal line.
Since there is no real source of DC on the Input of a 1959 I would suspect a failing V1 unless you are all covered up in synthetic clothing and do statically charge yourself and the Guitar/Pickguard but ussually this is then heard as crackle...

 

[william vogel]

Swap V1 tube.

 

[matttornado]

Swap V1 tube.

I mentioned in my OP that I did that already.

 

[matttornado]

If all guitars show a scratchy pot on this amp but not on other amps the problem is not the pot, it is in most cases DC on the signal line.
Since there is no real source of DC on the Input of a 1959 I would suspect a failing V1 unless you are all covered up in synthetic clothing and do statically charge yourself and the Guitar/Pickguard but ussually this is then heard as crackle...

Yeah I never though it was the pot. I never had any problems with static electricity in all of the 40 years I been playing so that is unlikely.

 

[matttornado]

If all guitars show a scratchy pot on this amp but not on other amps the problem is not the pot, it is in most cases DC on the signal line.
Since there is no real source of DC on the Input of a 1959 I would suspect a failing V1 unless you are all covered up in synthetic clothing and do statically charge yourself and the Guitar/Pickguard but ussually this is then heard as crackle...

There are no leaking DC anywhere that I'm aware of. None of the controls on the amp are scratchy. The amp works great and sounds incredible.

 

[william vogel]

There are no leaking DC anywhere that I'm aware of. None of the controls on the amp are scratchy. The amp works great and sounds incredible.

Have you measured for DC voltage on the cord without being plugged into the guitar. I know you say no leaking DC but you haven’t opened the amp.

 

[matttornado]

Have you measured for DC voltage on the cord without being plugged into the guitar. I know you say no leaking DC but you haven’t opened the amp.

No I havent but that sounds like a very good idea! if I do find DC, what would be the culprit?

 

[matttornado]

Have you measured for DC voltage on the cord without being plugged into the guitar. I know you say no leaking DC but you haven’t opened the amp.

I just recently restored the PCB and put the amp back together and while doing that, I checked that there were no leaking DC anywhere on The PCB. https://www.marshallforum.com/threads/1974-pcb-restoration-repair.124914/post-2233571

 

[matttornado]

Thanks for the help!