Wah with Limit Switch producing lots of Popping

[Nick C.]

I rehoused and modified a crybaby to use a LDR for wahing and a mini limit spdt switch instead of a stomp switch. The circuit switches to bypass when the rocker is heal down. Someone around here had the idea of holding the rocker against the switch with a magnet and it works great, but I'm having a lot of popping. Two questions for the wise folks around here.

What did I miss? Cap and/or pulldown on the bypass line? Pull down at the very output?

On the bypass arrangement, I added the input buffer to present a high impedance to the bypass input. I think it works ok, but not sure if it sucks tone. Problem is the lack of affordable mini dpdt limit switches. Does it make sense?

Thanks, Nick

[Myampgoesto12]

 Magnets can do weird things when placed near mechanical components in the signal path, or near a signal path in general. But those switches have a springy click as well.

A more elegant solution could be to use that switch to activate a relay bypass, but those CAN cause pop as well.

Perhaps a Boss style bypass circuit could be installed to remove the need to hold the treadle against the switch. That's a good bypass with basically no noise when switched since the switch isn't directly in the signal path.

[Nick C.]

Chuck, that's interesting, I never thought about the magnet field messing with the stomp box. And I am rocking some steel up and down near the magnet and the signal. If it messes with the signal, it would still do it in bypass too. Something to think about, but it doesn't seam to affect it too much.

The relay or transistor switching would probably be a better solution, but beyond me. The limit switch is probably very bouncy and when I hit the switch while playing it does make a little noise, but most of the pop is happening just the first time it's engaged after powering up.

I left out of my schematic a dpdt manual toggle switch I put in as a true bypass. When this is switched there's no pop. I just figured out that if I rock the treadle when in true bypass and then use the wah, these's no pop. It's a work around, but I'd still like to fix it since I usually don't use the toggle.

[Myampgoesto12]

Sorry that its been a while, been super busy..

Your limit switch is momentary right?

If so, 9v momentary Relay switching is really really simple to implement, its just risky as far as noise goes. You may have to try a few models of relays, and bypass styles( true bypass with effect input grounded when bypassed, or true bypass with effect input not grounded when bypassed, or basic "hardwire" bypass that the pedal has stock where the output is the only thing that's switched).

With a 9v dpdt momentary relay you have 6 terminals/pins (whichever type you go with) in the switching mechanism (lets call them pins 3-6) and 2 more for power to engage the relay (1 and 2). You would only need to wire your guitar  signal on its switching (3-6) pins just like you would on a stomp switch for true bypass. Pin 1 would be the voltage source for the relay. Pin 2 would go to ground, though the order shouldn't matter.

You would power the relay by putting voltage from the pedals power source to the common pin of the limit switch, then a wire from the from one of the other pins to pin 1 of the relay. And remember pin 2 of the relay goes to ground. You just have to know which pin of the limit switch will allow voltage to go across it while you are using the treadle for the effect. In this manor of wiring the relay has the longest life span since its only engaged for use of the effect.

Have you thought about spring loading the treadle and using a momentary dpdt stomp switch? You'd only lose the %^&*ed wah and walk away effect by doing this. And its fewer terminations.