anti-pop resistor with IC based circuit

All frequent questions on switching: true or not true bypass, transistor-based or mechanical.
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fishfude
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Post by fishfude »

Hi folks,

I was just wondering if it is necessary to have a 1M anti-pop resistor to ground when using an IC based circuit such as the MXR Distortion + (see image):

Image

I was also wondering if someone could give me a description of what the anti-pop resistor is doing when it's doing it's job.

Thanks,

ff

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Nocentelli
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Post by Nocentelli »

Capacitors store charge. An input capacitor can store charge when the input is disconnected in bypass. When the effect is engaged, the cap is reconnected and can discharge. This can cause an audible pop. An antipop/pull-down resistor is a permanent route to ground from the input side of the input capacitor. When switched to bypass, the cap can discharge to ground so popping is less likely. The value of the resistor should be high enough (typically 1M) so it doesn't bleed guitar signal to ground when the effect
is engaged.
All of the above also applies to the output cap, but since most dirt pedals have a volume pot at the output after the output cap with lug 1 connected to ground, the pot acts as an antipop resistor. You'll notice that any circuit without a volume pot at the end always has a resistor to ground after the output cap to perform this role.

As tot whether you need one on the D+, my instinct is that it can't hurt but it might help. 1M or 2M2 would be fine.
brownwhopping wrote:How can I learn by reading threads an making circuits, when some day I can see a lawsuit or somebody beat me in the face for that?

fishfude
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Post by fishfude »

Thanks again! That makes perfect sense.

ff

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