pull down resistor and input grounding

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pull down resistor and input grounding

Postby poiureza » 08 May 2017, 10:22

Hello,

Here is the 3PDT wiring I use for all my builds (pic from Gaussmarkov) :
Image

I ran across a situation where I'd like to have a bicolor status LED (bypass/on).
Implementation would be easy if I could use the entire center row of the 3PDT switch.
That in turn would mean I'd need to remove the wire that enables circuit input grounding in bypass mode.

AFAIK the sole purpose of input grounding is to avoid popping when you turn the effect on and off.
And it is only effective if popping is actually due to input capacitor leakage.
Yet the 1M pulldown resistor at circuit input is used for the exact same purpose.

I guess my question is : Isn't circuit input grounding at the switch + pull down resistor overkill ?
If so, can't I just leave the pulldown resistor and have my bicolor LED wiring on the 3PDT switch ?
poiureza
 
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Re: pull down resistor and input grounding

Postby plush » 08 May 2017, 12:23

Hi!

poiureza wrote:
AFAIK the sole purpose of input grounding is to avoid popping when you turn the effect on and off.


No. Input grounding is done to avoid self oscillation in some circuits, when they are bypassed.
It has nothing with switch on/off popping and you can omit it in most cases.
The most common anti-pop measure is 1-2m ohm pulldown resistor and power filtering cap (w led connected to 9v before the filter cap). In general, all counter-measures vary depending on the reason of popping.

poiureza wrote:If so, can't I just leave the pulldown resistor and have my bicolor LED wiring on the 3PDT switch ?


Yes, of course you can.
But I myself would add some sort of a transistor key to switch between led states and leave input grounding.

For this message the author plush has received thanks:
poiureza (09 May 2017, 12:35)
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Re: pull down resistor and input grounding

Postby poiureza » 09 May 2017, 12:34

Thanks, I hadn't thought about transistor switching. I'll check that :thumbsup
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