when a pull down resistor is not necessary?

[Toney]

I have been in the habit of adding a anti-pop pulldown resistor from the input to ground in all my pedals .
I feel I should know this one, but I'll ask anyway...

When a pedal such as the Orange Squeezer already has a 4m7 from input to ground in the layout, do I still add the standard 1m pulldown?

What's the range of resistance that "catches" pop transients?
And... is there any risk of effecting the input signal?

[bioroids]

If you already have a resistor to ground on the same side of the input cap, there's no need to add another. If you are afraid of the 4m7 resistor being to big to catch pops (i'm not sure about this), then just replace it with the 1M resistor. I mean, there's no need to put both in parallel, really (4M7 in parallel with 1M gives you like 824K).

I'm not sure about how large can be this pull-down resistor and still be able to catch pops. Anyone?

Luck

Miguel

[R.G.]

I'm not sure about how large can be this pull-down resistor and still be able to catch pops. Anyone?

This is one of those places where you have to understand the theory before you can come up with an answer other than easter-egging parts.

It depends on the input cap. Plastic film caps are usually quite low leakage and can have almost as big a resistor as you can get (10M to 22M). New electrolytics may only need a 4.7M, while old ones can need a 470K as the leakage rises.

You also have to define "catch pops". Some pops are either inaudible or unnoticeable even when present. In designing the Millenium bypasses I set myself a 2mv threshold. It's arbitrary, depending on the situation. In roaring hocky rink, you might not be able to hear ...any... pops, however present. In studio, the tiniest noise is unbearable.

[bioroids]

This is one of those places where you have to understand the theory before you can come up with an answer other than easter-egging parts.

I think that's always the case!

Thanks for the info. So it has nothing to do with the size of the cap

Luck!

Miguel

[R.G.]

So it has nothing to do with the size of the cap

Only vaguely, in that bigger electrolytics leak more than littler ones.  But a big new electrlytic will leak less than a smaller old one.

The insulator material makes a big difference.

[Processaurus]

One situation where you don't need a pull down resistor, and you still see people put them in, is when there is a volume control pot after the output cap.  Since it is a resistor going to ground, its redundant to put another high value resistor in there in parallel.  Not that it hurts anything, it just doesn't do anything.

[bioroids]

One situation where you don't need a pull down resistor, and you still see people put them in, is when there is a volume control pot after the output cap.  Since it is a resistor going to ground, its redundant to put another high value resistor in there in parallel.  Not that it hurts anything, it just doesn't do anything.

You're right. If its low value compared to the pot, can alter its taper...

Luck

Miguel