Thank you for trying to be so clear in your communication….sorry for my lack of understanding very well. I’m not sure what is going on here. Somehow the Quaverato is interacting with the PXL in a weird way, seeing that when it’s not in the signal path the issue doesn’t occur, no matter what pedals are in the signal path. I would love to find the schematic to the PXL to see what buffer circuit they are using.
You were very clear that the pedals that have been part of this issue contain opamps (“an actual physical DC-coupled electronic voltage amplifier with a differential input; also known as an OPAMP”). But you also described the buffer in a non-activated Boss pedal as “an opamp”. From the Boss service manual schematics we can see that Boss pedals use common collector discrete buffers, so I’m a little confused about what you are calling an opamp…are you just calling an active pedal, despite it’s particular circuitry, an “opamp”?. Either way, you said the jump does occur when a bypassed Boss pedal is powered on downstream of the Quaverato, so I’m assuming this volume jump also happens with discrete, non-opamp based pedals like a big muff, or LPB-1, or mosfet boost are on downstream of the Quaverato…is this correct?
One thing this might be related to is the phase of the Quaverato signal. If you look at the Quaverato schematic, you will notice that the output signal is out of phase from the input signal. But I’m not sure why only the Quaverato would cause a jump in the volume and not other pedals that flip the phase (like the LPB-1 set to unity gain, for example…which I suppose is something to check out). There is a way to mod the Quaverato to have in-phase output…it requires a lot of trace cutting and jumper wire running.
Another thing that crossed my mind is that the “silent switching” circuit on your pedal may not be operating correctly…possibly causing impedance issues. You can check this by removing C17, which will remove that circuit from the signal path. You’ll need to use a solder sucker to clean out the PCB holes (heat it up from one side of the board, suck from the other side of the board).
That’s all I can think of for now. Good luck!
-Brach