Question about kill switch pedal design

[irishstu]

Morning ladies and gents,

I found a really nice heavy duty momentary push switch and was thinking of making a foot-operated momentary kill switch pedal with it.

Here's my plan:



Now, I know that the best kill switch circuits will short the positive to earth rather than leaving the circuit open, and this will, of course, cause no damage whatsoever to anything further down the chain (i.e. whatever comes AFTER this pedal).

However, I'm wondering how this might adversely affect the output of whatever comes BEFORE the pedal. Obviously if this came straight after a passive pickup, then there's nothing to worry about, but what about if it comes after an overdrive pedal or something? Is shorting the output of the overdrive to ground going to damage it? The reason I ask is that one of my guitars has a treble booster built in.

I realise a three-legged switch would be a good option (Common/NO/NC), as at the same time of shorting to ground, I could disconnect from the input signal, but unfortunately this (very nice) stomp switch only has two legs.

So I guess I have two questions:

1) Could this mess up whatever's before it in the chain? (I'm assuming the answer is yes)
2) Is there anything passive I could add to this circuit that would prevent any damage?

I was thinking that maybe a very small resistor either in line with the input signal, or between the switch and ground might be a possible safety option, like 10 ohms or something, but I'm really just guessing here.

Thanks for any advice you can give.

Stu

[anchovie]

Shorting the output to ground is exactly the same as turning the volume pot on the pedal or guitar before it to zero. I don't think anyone's blown up any gear before by turning it down!

[CynicalMan]

Most volume pots are wired with the 1st lug connected to the circuit, the 2nd lug connected to the output, and the 3rd lug connected to ground. Therefore turning the volume pot all the way down on a stompbox will short the input of the next stompbox. The volume pot would make the maximum resistance to ground the value of the volume pot and the minimum resistance the value of the volume pot in parallel with the input impedance of the next circuit. At no point would the circuit output be shorted to ground unless the input of the next circuit was shorted to ground.

Responding to irishstu, I have never had any problems having a kill switch after an effect. Putting a 10k resistor in series with the input would probably protect the previous stompbox, although you might have a small volume drop.

[anchovie]

Thanks for clarifying, I see now how it's the next input that's being grounded.

[irishstu]

Responding to irishstu, I have never had any problems having a kill switch after an effect. Putting a 10k resistor in series with the input would probably protect the previous stompbox, although you might have a small volume drop.

Thanks CynicalMan. In that case do you think I could get away with a resistor of a smaller value than 10k?

[CynicalMan]

Responding to irishstu, I have never had any problems having a kill switch after an effect. Putting a 10k resistor in series with the input would probably protect the previous stompbox, although you might have a small volume drop.

Thanks CynicalMan. In that case do you think I could get away with a resistor of a smaller value than 10k?

You could, but I don't think it is necessary. Given that most effects have an input impedance of about 500k, and that most amps have an input impedance of about 1M, you'd lose 0.172 dB with an effect following the kill switch and you'd lose 0.0864 dB with the amp. Still, if that is too much, you could reduce it. I can't see you losing more than 1dB of signal.

[fuzzo]

I did the same things (just to see) with a boss switch and it worked good, any problems with other pedals in chain.

[irishstu]

Thanks again.