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DIY Stompboxes => Building your own stompbox => Topic started by: Derringer on July 09, 2015, 08:32:33 AM

Title: Question about switching with grounded inputs and pulldown resistors
Post by: Derringer on July 09, 2015, 08:32:33 AM
If a bypass switch is wired such that the input of the effect is grounded when the effect is bypassed, is a pulldown resistor still needed from the effect's input to ground to prevent switch pops? Let's assume that the output of the effect is a volume pot so that the output doesn't pop when switched.

Title: Re: Question about switching with grounded inputs and pulldown resistors
Post by: samhay on July 09, 2015, 09:43:00 AM
It might do - if the outside (not circuit side) of the input cap is pulled high for some reason while the effect is engaged then it will pop when the effect is bypassed, as it will be pulled to ground.
Title: Re: Question about switching with grounded inputs and pulldown resistors
Post by: kleber.kag on July 09, 2015, 09:57:24 AM
In this case a series input resistor would prevent it to short to ground popping.
Title: Re: Question about switching with grounded inputs and pulldown resistors
Post by: R.G. on July 09, 2015, 10:43:53 AM
It depends on what it's fed from on the input. If the thing feeding the input has a series capacitor (as in, it's another effect, not a guitar) and that output is not pulled down, then both caps will leak when the effect is engaged. Also, my day job has taught me that users will do weird sh... er, stuff   :)  and you can count on at least one of them to do the worst possible thing you could imagine.

For the cost of a resistor, it makes sense to put a pulldown on it whether it nominally needs it or not.
Title: Re: Question about switching with grounded inputs and pulldown resistors
Post by: Derringer on July 09, 2015, 11:47:01 AM
Quote from: R.G. on July 09, 2015, 10:43:53 AM

For the cost of a resistor, it makes sense to put a pulldown on it whether it nominally needs it or not.

and that's what I did when I built the thing, just in case  :icon_mrgreen:

thanks folks!