anti-pop resistor with IC based circuit

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anti-pop resistor with IC based circuit

Postby fishfude » 08 May 2014, 14:35

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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Re: anti-pop resistor with IC based circuit

Postby Nocentelli » 08 May 2014, 16:23

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.
mmolteratx wrote:absolutely zero commercial use allowed. If I find anyone selling these, I'll fly to your house and kick you in the nads. And you may or may not find yourself in trouble.

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Re: anti-pop resistor with IC based circuit

Postby fishfude » 26 May 2014, 16:58

Thanks again! That makes perfect sense.

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