How can I tame an output pot?

[BuddytheReow]

Many circuits out there have an output cap followed by a volume pot. Like so....



Cranked wide open, there are no issues. However, as you turn the knob down you start to change the tone since this also acts as a passive filter. Is there a way to remove the tone shaping aspect but keep the volume change piece? I KNOW this was discussed somewhere here, but I can't seem to find the thread.

Is it simply putting a cap between 2 of the pins? I THINK that's what was talked about?

Thanks,

BuddytheReow

 

[JamieJ]

If you use a a 1u or 2u2 output cap and a 100k pot it should make the filter redundant for guitar frequencies.

At 25k it filters at 2Hz. 50k is 1.4Hz and 75k is 1Hz with a 2u2. So with this value you don’t have a useful filter as everything above these values is allowed to pass on the output, so you only end up getting the decoupling benefit from the cap. Similar effect at 1u with 75k filtering at 2.1Hz and 25k at 6.4hz. You could place a simple fixed HPF just before the output cap if you do need to take some bass frequencies out on the output if needed.

With a typical 100n output cap at 25k it forms a HPF at 63Hz which may be helpful for you to get rid of some problematic low end.
220n filter point is at 29Hz at 25k on the pot.

I think it only really becomes a big problem for lower cap values like 10n - where at 25k the HPF would be at 637Hz.

 

[BuddytheReow]

thanks @JamieJ

I should clarify. This is probably going on a circuit for bass, so I need to preserve the low end. If it means anything this is also going on a tone bender/fuzz face circuit

 

[jesuscrisp]

If you want to be very sure to conserve your low end, just use a 10uF cap. But realistically speaking, 1uF is plenty even for bass.

 

[JTEX]

Increase the cap 10x and reduce the pot to 10k. A 100k output pot on the output of a circuit results in a way too high output impedance once you turn the pot down and the pot's top-to-wiper resistance then appears in series with the output. High output impedance forms a low pass filter with the capacitance of the cable following the output (which is often into the nanofarads), rolling off the high end. In pretty much no situation is a volume pot higher than about 25k justified on the output of an active audio circuit. 10k is better. 5k even better. Just make sure the output stage has no trouble driving the pot's resistance.