Volume pot (voltage divider) and pull down resistor

[bthm3288]

Hi all, first post here. I've tried searching but have not found definitive info on this. My question is this - on circuits that have a volume pot on the output (wired as voltage divider), is it necessary or beneficial to also have a pull down resistor? For example, the LPB-1 has a 100k pot on the output, does this effectively function as a 100k pulldown resistor? If so, is 100k too small a resistance, and would the circuit benefit from a 1M or larger pulldown resistor?

Thanks in advance!

[R.G.]

If you have a volume control "outside" the final signal capacitor, it will also act as a pull-down resistor, and no other pull down resistor is needed. The smaller resistance is not a problem.

[bthm3288]

Thanks for your reply RG. So any circuit that has a voltage divider after the output cap does not need or benefit from a pull down resistor? For example the son of screamer uses a 10K volume pot on the output.. no need for a pull down there? 10K is sufficient? Very interesting.

This might explain why, after adding a 100k volume trimmer to the output of my chorus pedal (to adjust unwanted volume boost), it also fixed the switch pop problem I was having on that pedal...

Thanks!

[willienillie]

10K is sufficient?

The lower the resistance, the better it works.  It's there to bleed stored DC voltage from a cap to ground.  The reason you usually see 1M and higher used for pulldowns is that they are usually added on to a circuit that already functions as intended, and the higher resistance has less or no effect on the sound of the circuit.  If you used a 10K pulldown at the input of most circuits, it would dramatically lower the input impedance and alter the tone in an undesired way.

[bthm3288]

10K is sufficient?

The lower the resistance, the better it works.

now that I think about it, I see what you mean.. the output cap will drain faster with a lower resistance, correct?

So it's safe to say that that on any of my diy pedals that use a volume pot on the output (voltage divider downstream of the output cap) that I don't need an output pulldown resistor. And since I generally ground the input of the effect when bypassed, there's no need for an input pulldown resistor there either, correct?

thanks!

[willienillie]

You got it.