AB Switch + Question

[bcalla]

I had a great idea that grew into something much larger. It started out as a simple selector switch – 2 basses going into 1 amp, with a stomp switch to select which bass. I remembered that I had a GPCB Silent Tuner and Buffer PCB, and decided that a tuner out with mute would be a nice feature. When I read my notes for this circuit I found the mod that allowed you to replace R4 with a pot to adjust the gain. So my next idea was to have 2 pots – 1 for each input – which would allow me to preset the gain for each instrument.

I figured out a wiring plan – see below – and it works pretty well, with one exception noted below. The black wires are directly from the build doc. The colored wires are to support the instrument and pot selection.  The center strip of the stomp switch lights one of 2 LEDs to indicate which instrument is active.  I didn't want to clutter this diagram with the LED wiring.  I also omitted some of the grounds from the diagram.



There is one problem that I'm hoping to solve. If I don't mute the output first, there is a loud thump when I switch between instruments.

Does anyone have any suggestion to eliminate the thump?

[PRR]

> thump when I switch between instruments.

ANY two instruments?

[bcalla]

I have only tried it with 2 basses.  I'll try a couple of guitars & see what happens.

[bcalla]

I just tried it with 2 guitars with the same result.  I also did it with nothing plugged in to either input, and still got a thump.

[duck_arse]

perhaps the gain pots going outta circuit is the cause. you might need to trick-up a value for R4 and the pots that still allows yr wanted gains.

[Seljer]

Battery or DC adapter powered?

For good measure disconnect the LED switch somewhere to see if that inrush of the current required for the LED that's causing your thump