Switch to swap op-amp feedback resistor *POP*

[PhiloB]

I have a friend that wants a simple pedal to set 2 different vol/gain levels and provide a buffer.  I thought a simple approach would be to use an op-amp and vary the feedback resistor.  I decided to lay it out as below in hopes to keep the impedance low on output.  He wants the max volume to be unity gain.  My problem is there is pop when I switch between pots.  I suspect DC build up.  I tried using "pull-down" resistors either side of the pots with no luck.  Do I need to use 2 separate sides of the op-amp and switch between op-amp?  Or can I utilize the current layout and deal with the DC?  Thanks for any help.

[PRR]

Your plan goes Open-circuit, "infinite gain", while switching. That will pop.

Try this. The in-between mode, while the switch contacts are neither here nor there, is a low-gain condition.

[PhiloB]

That makes a lot of sense.  Thanks PPR, I'll give that a shot in the morning!!

[PhiloB]

I gave this a shot this morning and it helped significantly.  Thanks for the suggestion.  There is still some pop but it is much better.  Not sure I can expect a mechanical 3pdt switch to have NO noise.

[PRR]

R4 should be *zero*. 1Meg may, depending on the op-amp, be a very significant DC error which will change with gain condition.