cap popping on a 1p12t switch > pull down theory

[ulysses]

hey guys

in one of my home brew designs ive been using a 1p12t rotary switch to go through 12 caps basically to see how different caps effect the sounds in different positions. each time i rotate the knob i get a pop.

i tried using a resistor to limit the pop but that affects my circuit as well as stopping the pop.

apart from actually stopping the guitar before turning the cap changing switch is there anything i can do to stop the pop noise. i presume it the discharge of the caps or something like that.

thanks guys
ulysses

[Processaurus]

Did you try bigger resistors (1M, 2M, 4.7M) from each of the 12 poles to the common lug?

The caps are leaking DC onto the side that is connected to the switch lugs, and when you switch to them, there is a big transient from the change in DC level in your audio.  Its the same idea as the 1M-4.7M pulldown resistors on modern true bypass effects.

[R.G.]

The standard practice when switching between a number of caps to be selected is to put a high value resistor in series with each cap, then to use the switch to short out the resistor of the cap you select. The resistors hold the same DC voltage on every cap. All the switch does is remove the high resistance for a low one to allow signal through the selected cap. In this way the caps never have a different DC voltage, so there is no discontinuity to cause a pop when you switch.

[Gus]

Are you using a break before make?

If so try a make before break

[Mark Hammer]

I find the best strategy is to place the caps in series and use a switch to short out various caps in the series to yield different series capacitances.  Since nothing is left with a "hanging" free end, there is no pop.  Trouble is, that's a whole lot easier to implement when you're using a 3-position toggle than a 12-position rotary.

[ulysses]

thanks for the replies guys.

rg do you have a schem with the series wiring? i am a little confused..

i tried wiring a resistor on each cap in series but it seriously degraded the effect to the point where it was unnoticable..

mark i have studied your theory before on a circuit with 2 switching caps.. figuring out the values for 12 caps would prob be difficult if even possible to get standard values for all 12 caps.

thanks guys
ulysses