Relay Switching And Pop Noise

[kryfcn]

Hi guys. Im having trouble with pop noise . what would be wrong here? As you can see there is dc on the relay switch comes from the PI grid. Is that the problem? I tried to put there different values of caps but pop noise still there and amplifier didnt sound the same as before in negative way. Is there another switching circut that allows me to be free to keep dc on the switch without pop?

Many Thanks.

[R.G.]

Yes, DC on the relay is most likely the problem. It allows you to open the series path to a capacitor, or more than one cap. The cure is usually to add big-value resistors from the opened end of the cap to the voltage it would have if the switch were closed.

All capacitors leak a little. A capacitor with DC voltage across it will slowly leak down if it has no path to keep it charged. A relay switch opening the cap will allow it to leak down from the DC idle voltage it had before the switch opened. Then when the switch closes again, the amount the cap leaked down is introduced as a signal - a pop.

This is a very common issue with stomp boxes. The cure is to introduce a large resistor from the end of the cap to the voltage it "should" have with the switch closed. This keeps the cap at the idle voltage, so no pop happens when the switch is closed.

There is one additional issue with relays. The sudden change in voltage on the coil can couple to the signal on the contacts. This varies from relay to relay, but is worst with physically big relays. Small DIP style relays usually don't have much of this. This is more of a (click) than a pop in most cases.

[kryfcn]

Thanks for the ideas R.G.

Which cap would cause the Pop in this scheme?
C10 or C17 ?

[R.G.]

Try this to start:
1M to ground from the relay end of C10 and C17.

The PI is a bit more complicated. I would add a new capacitor, 0.1uF, in series at C2 of the FXloop relay to the PI input. Then I would add a 1M resistor to ground from B2 and C2 of the FXloop relay. This ties the free end of C19 and the new cap to ground all the time, in spite of the relay switching.
The new cap to the PI input is to break the DC from the PI input and allow the relay switched ends of the caps to be tied to ground.
I think this will cover it. Yell if it doesn't.