Question about switching with grounded inputs and pulldown resistors

Started by Derringer, July 09, 2015, 08:32:33 AM

Previous topic - Next topic

Derringer

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.


samhay

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.
I'm a refugee of the great dropbox purge of '17.
Project details (schematics, layouts, etc) are slowly being added here: http://samdump.wordpress.com

kleber.kag

In this case a series input resistor would prevent it to short to ground popping.

R.G.

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.
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

Derringer

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!