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Popping octave switch on Foxx Tone Machine

7/23/2003 8:26 PM
BillF Popping octave switch on Foxx Tone Machine
Hello all: I've built a Foxx Tone Machine copy (per RGK schem), works fine and the tone is great, however I get a big POP every time I hit the octave up switch. I am using a regular DPDT footswitch for the octave up. Has anyone encountered this before, and more importantly, can anyone suggest a fix?  
Guitar is a Fender EC Strat, amp is a Twin Reverb.
8/14/2003 3:31 PM
Mark Hammer

In principal, you shouldn't get a pop since every cap associated with the switch contact points in question have a place to drain as near as I can tell Switch popping is generally related to having a cap with a "free end" so that stored charge has nowhere to go until switch closure. The generic solution for switch-popping on inut and output jacks is to wire up a high value drain-to-ground resistor to what would normally be the "free" end of the relevant cap. The only thing I can see that would be possibly pertinent here is the 10uf cap connected to the "input" side of the sustain pot. The + side has a path to ground via a 100k resistor, but it has to pass through a diode first and that may constrain exactly how much current can drain off.  
Just for the hell of it, try tacking on a 2.2M (or higher) resistor from the junction of that 10uf cap and the diode and 100k-resistor-from-V+ to ground. That is the resistor goes between the "free" end of that cap and ground, bypassing the diode and its own 100k resistor to ground. The effect should be to bleed off stored charge that has nowehere to go because of the diode without having much audible effect on the functioning of the diode.  
Tell us what happens.
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