General Tso wiring with buffer switch

[mcf]

I'm building a General Tso with the 3PDT breakout board with buffer switch so I can switch between true bypass and buffered bypass. I think this should work fine, but I'm a bit unsure of how to wire the mute pad on the main PCB.

From the build doc, I see that MUTE should be grounded when the pedal is off. Since the center lug of the 3PDT is ground, and the bottom middle lug is unused, I think I can just hook up that bottom middle lug to the MUTE on the PCB and get the exact wiring in the build doc when the switch is at BUFFER. I drew some lines to show the trace of the breakout board and how I would connect MUTE.



When set to TB, I'd get the usual 3PDT true bypass wiring, except that the PCB input would not be grounded when the pedal is off. I don't think this is a problem with the Tso circuit, but maybe someone could confirm?

I noticed in the description of the breakout board it says "Grounds PCB input in bypass to reduce noise", but unless I'm mistaken, I don't think any of the 4 possible switch positions will ground the PCB input.

And while I'm here, I was wondering if anyone could explain the function of MUTE on the Tso circuit? Looking at the schematic, it essentially shorts R20, but I don't understand why.

Thanks in advance for any help!

 

[mcf]

Just an update for anyone else who might want to use this breakout board with the General Tso: I ended up wiring this as I described above and everything seems to be working fine.



With my limited circuit analysis skills, I believe that grounding MUTE essentially removes the AC component of the + input of the opamp, muting it. Otherwise, if SW1 is in blend mode, some of the compressed signal would leak across the balance potentiometer into the buffer output. I think without grounding MUTE, you'd get the same result as the balance knob all the way down. In practice, I couldn't really hear any difference between grounding MUTE and not when in buffer bypass mode (maybe a tiny change in noise?).

I also tested the difference between grounding the PCB input or not in true bypass mode, and this had absolutely no effect, so this is nothing to worry about. Still, I think the description of the breakout board should be updated, since it claims to ground the PCB input, but this doesn't seem to be the case.