Fatpants Leaking Voltages When Bypassed

[ddog]

I have a Fatpants (2013) that has recently started making pedals placed after it 'pop' when I hit their stomp switch. This only happens to the pedals placed after, not the ones before.

I checked the voltages - when the pedal is bypassed there is  3.5V - 4V on the tip of the output jack which drops to 0V when I turn on the pedal. Turning the knobs (FAT, LVL) or the switches (SOFT, BODY) has no effect on the voltage.

The pedal is currently wired in buffered mode (diagram). I was thinking of re-wiring it into true bypass to fix the problem.

Before I do that, is there a possibility that a component is faulty (C2?, C7?, other? and which one do I check) or maybe the switch became faulty (how would I check that?). I rather switch out a component than rewire the pedal into true bypass.

Here is the schematic:




Thanks for the help!

[Zerro]

Signal at Buffer output is hanging out, without galvanic connect with ground via some resistor. I suggest add at this output resistor to ground, cca 470k, as shown at picture I attached. Maybe experiment with value of this resistor - maybe even 22k will be enough :@)

[madbean]

Signal at Buffer output is hanging out, without galvanic connect with ground via some resistor. I suggest add at this output resistor to ground, cca 470k, as shown at picture I attached. Maybe experiment with value of this resistor - maybe even 22k will be enough :@)

This should not be needed. Buffered bypass wiring (not shown) grounds R7.

My guess is a leaky C2 cap.

[mauman]

I agree with Madbean, the buffered bypass wiring shown should be grounding the nexus of C2/C3/C4 during bypass via the 2 lugs of the footswitch circled.  Verify that the foot switch is grounding lug 6 to lug 5 during bypass, if it is then replace C2.

[ddog]

With the 9V plugged in:
-when bypassed, 5 and 6 are 'momentarily' grounding, that is when I set dmm for continuity measurement I get a short beep, (and the LED turns on). Sometimes I get chirping (ie multiple short beeps)
-when turned on 5 and 6 is continuous

Without the 9V:
-when bypassed, no ground connection between 5 and 6

I'll replace C2 and report back. It seems I used a tantalum capacitor for C2 (oops), Ill try to replace it with a metal film. I'll probably replace the C7 one as well, since I used the exact same type of capacitor for it as C2.

[mauman]

With the 9V plugged in:
-when bypassed, 5 and 6 are 'momentarily' grounding, that is when I set dmm for continuity measurement I get a short beep, (and the LED turns on). Sometimes I get chirping (ie multiple short beeps)
-when turned on 5 and 6 is continuous

Without the 9V:
-when bypassed, no ground connection between 5 and 6

I'm counting the foot switch lugs like this:

1   4   7
2   5   8
3   6   9

During bypass, there should be shorts between 2/3, 5/6 and 8/9, as read with ohmmeter or continuity test, without 9V power to the pedal.   If 5 & 6 aren't shorted during bypass, the foot switch is faulty and would result in the trouble you describe.  If they're ok, it's probably C2 as you suspect.   

[ddog]

Thanks mauman. Yep looks, like it is C2. 5 and 6 are shorted during bypass.

[mauman]

 

[Zerro]

C2 would be wrong, it is second possibility. But try that hack with resistor at output bypass.

[ddog]

I took a look back on my board C2/C7 are actually MLCC (makes a bit more sense than tantalum).

I've also noticed that the output jack isn't always outputting a voltage when bypassed. What tends to happen is I can use the pedal as normal (meaning the pedal won't cause the pedals in front to pop), then suddenly I will get a volume drop followed by a volume recovery and now all the pedals in front will start popping. If I take the pedal out of the chain and try again next day, the behaviour resets.

C2 would be wrong, it is second possibility. But try that hack with resistor at output bypass.

I've been playing around with this hack. Does the size of the resistor matter with respect to tone? Ie is there any auditory difference between 470k vs 22k?

I've managed to reduce the output voltage to 0  if I use a 270R resistor. Im sure I can achieve the same result if I use a 10R as well. Is there any advantages to using a lower value? (or higher value?)

Is there any benefit to achieving a 0.00V? I can achieve a 0.05 or a 0.2 voltage; will these also cause a large pop? Is there a risk to continuously output such voltages (via the output jack) to other pedals / amps?

[Zerro]

Hallo, ddog. This discharging resistor at bypass output must be from cca 22k - 470k. Not lower. Lower values could spoil output signal from input buffer to second stage and from bypass output too. At buffer output after C2, at 1k resistor, going to buffer output, there is no reason to find here DC voltage. Maybe for a moment, before the electric charge at C2 is not discharged. Only AC voltage from signal will be here. What kind of signal is at buffer output after C2, when there is no signal at input? In still stage, after C2 cannot be resistent DC voltage. And connecting of that switch before second stage to the ground won't reset some DC voltages at buffer output, in any way. This is why I recomended to add that discharging resistor at buffer output. But this cannot be at zero or too low valuse - this would shorten signal to ground.

Fiddle around those values I said before and controll that output pluck. I suppose that bypass/fx switch is connected properly  :@)