Hi & Low switch pop

[jmusser]

I just built Tim's Phuncgnosis circuit, and all is well except the high and low switch. When I switch between the two choices, I get a nasty pop. Since this is not a bypass switch problem, I'm not sure exactly what to do about it. I'm afraid if I put some sort of pull down resistor in there, that it will screw up the tone function. This is the first circuit I've had with this problem, but it's also the first one to switch LEDs too, instead of caps.

[jmusser]

I just thought iId see if I could get this thread back up front of the pile to see if someone could steer me in the right direction, in case this subject has already been beaten to death before.

[gez]

Not familiar with the circuit but whenever I've had popping when switching components in a wah filter I've usually had to resort to electronic switching rather than mechanical.  Set the switch up so that the thing turns on 'slowly' by using a cap which ramps up/down.

Might be a simple solution here, but as I said I'm not familiar with the circuit.

[toneman]

well, I haven't actually built the Phuncgnosis(what a name, huh?),
but pops happen because of DC level shifting.
Since everything thru the output opamp is AC coupled,
it could B the Vr bias.  Check with a digital meter to make
sure Vr is 1/2 of supply.  U might make Vr slightly adjustable to move
it up or down a fraction of a volt.   But that's complicated.
B4 U try that, try hanging a load on the output opamp.  
Say a  47K ohm at the output of U1b to gnd.
U1b is just driving the .1 cap.  It has no load.
Try it and letus know what happens.
staybalanced
tone

[jmusser]

Thanks guys. I will add that resistor, and see what happens. That circuit is on Tim Escobedo's Circuit Snippet site in the "Links" section of this forum, for the guy who's not familiar with it. It's a pretty good Auto Wha, and has plenty of quack. If the pop doesn't go away, I'll probably just use the high end selection, and forget the low end. To me, the high tone really brings out the essence of the effect.