Hearing Volume pot wiper noise in active guitar circuit.

jwhmca

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This is an active EMG style guitar tone circuit. The strange thing is I can hear the "wiper" of the tone potentiometer. It almost sounds like a dirty pot, but for sure it's not. It's not a crackling sound, it's a smooth "crrrrrrrrrrrr" sound when you turn the wiper. The control is brand new, and I have tried 3 others.

The wiper noise is still there when the guitar volume is down. There are other active circuits in the guitar.

Where should I start looking for an issue. Would a constant DC voltage on the pot make this type of sound? Is there any other way to "hear" the wiper of a pot?
 

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CJ

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capacitor feeding the pot needs to be replaced, it is leaking a bit of DC into the pot,

 

abbey road d enfer

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jwhmca said:
This is an active EMG style guitar tone circuit. The strange thing is I can hear the "wiper" of the tone potentiometer. It almost sounds like a dirty pot, but for sure it's not. It's not a crackling sound, it's a smooth "crrrrrrrrrrrr" sound when you turn the wiper. The control is brand new, and I have tried 3 others.

The wiper noise is still there when the guitar volume is down. There are other active circuits in the guitar.

Where should I start looking for an issue. Would a constant DC voltage on the pot make this type of sound? Is there any other way to "hear" the wiper of a pot?
If your schemo is accurate, the cap that goes to pin 5 is reversed. + pin should go to the right.
 

SSLtech

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Could be a leaky cap... -COULD be. -A single DVM measurement would prove or disprove.

However, it might also be DC leaking BACK from the following stage.
 

JohnRoberts

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Most likely suspect is DC getting into the pot from somewhere.

less likely scenario, I have seen circuits that would oscillate transiently during wiper bounce... most pots use multiple wiper fingers in parallel to reduce possibility that all wiper fingers are airborne at same instant. I have seen this noise mechanism in an EQ with marginal pot wiper design. 

Another low probability scenario is just very high gain with granular pot element resistance that is lumpy and causes signal jumps when turned (more likely in volume pot than EQ)

JR
 

jwhmca

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I have built a few of these and they all have the noise but only when there are other active circuits in the guitar. I'm going to test the DC level on the pot, but thought i would make the quick comment that it SOUNDS clean when in a passive guitar circuit.

Could I / Should I put a cap on the output of the pot?

CJ, do you think the cap being wrong would cause the problem?
 

abbey road d enfer

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jwhmca said:
I have built a few of these and they all have the noise but only when there are other active circuits in the guitar. I'm going to test the DC level on the pot, but thought i would make the quick comment that it SOUNDS clean when in a passive guitar circuit.

Could I / Should I put a cap on the output of the pot?

CJ, do you think the cap being wrong would cause the problem?
I wrote: "the cap that goes to pin 5 is reversed." It is sufficient to create DC. Have you checked that?
 

jwhmca

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CJ said:
capacitor feeding the pot needs to be replaced, it is leaking a bit of DC into the pot,

Well, that was it... I original found the first cap off the Input from volume pot to be backwards. How are the rest of them?
 

CJ

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ARDE had it figured, flip the circled cap>

 

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