Dual Gain Control Footswitch Pop

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mboyd43

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Working on a Sansamp vero but with 2 gain control pots selected by a 3pdt footswitch with an LED. Getting a nasty switch pop on it, also a pop on the on/off 3pdt but doesn't seem as bad. It is also one of 3 effects in a box but the other 2 function normally. I've tried connecting gain 1 from the board to each pot via their own wire and gain 1 and gain 2 to the 3pdt. Also tried all 3 gains to a 4pdt. Tried disconnecting both LED's. Any ideas how to tame the pop? Much appreciated

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Tech 21 SansAmp GT2

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Probably not avoidable, to some extent.
1)Does it do it in all 3 mods/modes(clean, high gain, hot rod switch)?
2)Is it significantly worse on the higher gains or the same? If it's worse on the high gain(middle switch middle position in ppcb schem), it's probably DC leakage from C7. You can check for DC present between the wiper and ground. If that's the case, replace the 2u2 with a 1u film cap. Shouldn't be much audible difference unless you're playing 7-8 string. even then it will be negligible.
3)What if you disconnect the LED/CLR(just break the LED circuit somewhere)? Any better?
Are you switching all 3 lugs on both pots?
PPCB build doc link
 
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One idea is to use LED/LDR combo as “switches”. They have just enough lag that you shouldn’t get a pop. You’ll have to cover the LED/LDR combos with heat shrink tone so they don’t bleed. In this case with 100k pot, the full dark and bright LED on resistances should work fine. Just have your stomp switch the LEDs. You’ll want to “switch” both the lug3s and lug2s in this case, because if you had 2 100k pots in parallel, it would make 50k, and that would mess up the filtering frequencies.
 
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jwin615 said:
Probably not avoidable, to some extent.
1)Does it do it in all 3 mods/modes(clean, high gain, hot rod switch)?
2)Is it significantly worse on the higher gains or the same? If it's worse on the high gain(middle switch middle position in ppcb schem), it's probably DC leakage from C7. You can check for DC present between the wiper and ground. If that's the case, replace the 2u2 with a 1u film cap. Shouldn't be much audible difference unless you're playing 7-8 string. even then it will be negligible.
3)What if you disconnect the LED/CLR(just break the LED circuit somewhere)? Any better?
Are you switching all 3 lugs on both pots?
PPCB build doc link
Click to expand...
It does do it in all modes/settings pretty consistently. I have also tried disconnecting all LEDs and no difference. First I tried switching all 3 lugs on a 4pdt, then tried just Gain 2 & 3 on a 3pdt and pop was the same. I'll try switching C7 anyway, see if that changes anything.
 
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If it pops in all 3 settings, it's not C7.
Wait! I had the wrong switch in mind! It's the Mic position switch that proceeds the drive pot.
Does changing it's position change the switch pop? If it's worse in the middle position(assuming your layout follows the ppcb schem) then I would suspect C7. Sorry. Not sure how I mixed those up.
Otherwise:
Try tacking 2x10Meg on the switch, 1 onto each switched pot lug
Lug 3 pot 1 to lug 3 pot 2
Lug 2 pot 1 to lug 2 pot 2
Keep the lug 1s independent with their own resistors to ground(R9 in ppcb schem).
there will be a little bit of interaction between the pots but it should be very little. Just lay the resistors across the 3pdt and tack them on to test. That way it's easily reversible in case I'm a idiot.
It likely won't 100% cure the pop but it may lessen it. There's a lot of gain after this switch position so I think it's likely unavoidable but putting the 10meg resistors there will at least resolve the potential difference some, kind of acting as a make before break.
Or may not do anything. But it's the last idea I have. Good luck!
 
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phi1 said:
One idea is to use LED/LDR combo as “switches”. They have just enough lag that you shouldn’t get a pop. You’ll have to cover the LED/LDR combos with heat shrink tone so they don’t bleed. In this case with 100k pot, the full dark and bright LED on resistances should work fine. Just have your stomp switch the LEDs. You’ll want to “switch” both the lug3s and lug2s in this case, because if you had 2 100k pots in parallel, it would make 50k, and that would mess up the filtering frequencies.
Click to expand...
I've been investigating solid state relays (SSRs) as well for my amp builds, which do not experience pop. I've been using opto-isolators for a while for silent switching.
 
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