On Volume Pot Values and Resistance

[kapsel]

Hi guys,

Two noob questions on volume pots, I guess they are simple but I can't really understand. I tried to read "the secret life of pots" article and I think I should burn down my A levels and uni degrees Anyway.

1. What is the relationship between the resistance value of a volume pot and the level of output? I mean what would happen if i used a 100k pot or a 10k pot where a schematic says 50k pot? Is there one standard answer for this or it depends on the circuit/ schematic?

2. Regarding the following schematic (modded Electra Distortion): I built that and it works fine but I was thinking to put it in an enclosure without a volume pot, but with a fixed volume level like the one it now has when the pot is maxed. How do I do that? Do i just remove the pot and wire the output after C2? Do I need to add a resistor of 100k (same value as the max value of the pot)?

Any help will be appreciated.

Cheers!

[drolo]

Hi Greg,

In your example, you should replace the pot by its equivalent resistor if you want to achive the same result as you get with the volume maxed.

The volume pot ideally should just act as a voltage divider for the output signal but some circuits are more sensible to the volume pot value you hook up than others. Especially when they have a high-ish output. A smaller value will for example load down a circuit like the Fuzz Face resulting in overall less treble and volume. A circuit using OP-amps like the tube screamer will be far less (or not at all?) influenced by the pot value, because it has a low output impedance.

[Gus]

here are two graphs from a sim. The same circuit only the volume control was changed.  The 390pf and 470k after the gain stage is 10 feet of 39pf a foot cable and a 470k load.

100K

500K

[mistahead]

Consider the output before the pot the main "pipe" as we hit the pot its a Y junction (in most volume controls you see here) - some of the signal passes through the "left" side of the junction to the output lugs/next stage, the rest of the signal passes through the "right" side of the junction to GND (dumped for all intents and purposes here).

Considering the total "width" of the junction will impact on how much signal can flow through the "pipe", and then start splitting that out from that junction to the lugs/next stage and dumping portions of it.

Gus has visually shown the outcome of playing with that "Y-junction's" "width" - but hopefully this will get you thinking / visualising it too.

[Canucker]

Hi Greg,

In your example, you should replace the pot by its equivalent resistor if you want to achive the same result as you get with the volume maxed.

The volume pot ideally should just act as a voltage divider for the output signal but some circuits are more sensible to the volume pot value you hook up than others. Especially when they have a high-ish output. A smaller value will for example load down a circuit like the Fuzz Face resulting in overall less treble and volume. A circuit using OP-amps like the tube screamer will be far less (or not at all?) influenced by the pot value, because it has a low output impedance.

Did you just say that as you turn up a fuzzface it gets bassier? I'm not trying to be a smart ass.

[mistahead]

Hi Greg,

In your example, you should replace the pot by its equivalent resistor if you want to achive the same result as you get with the volume maxed.

The volume pot ideally should just act as a voltage divider for the output signal but some circuits are more sensible to the volume pot value you hook up than others. Especially when they have a high-ish output. A smaller value will for example load down a circuit like the Fuzz Face resulting in overall less treble and volume. A circuit using OP-amps like the tube screamer will be far less (or not at all?) influenced by the pot value, because it has a low output impedance.

Did you just say that as you turn up a fuzzface it gets bassier? I'm not trying to be a smart ass.

I think what was said is that using a lower value VR for the volume divider can result in trebble and volume loss, possibly is a fuzzfaece

[drolo]

Hi Greg,

In your example, you should replace the pot by its equivalent resistor if you want to achive the same result as you get with the volume maxed.

The volume pot ideally should just act as a voltage divider for the output signal but some circuits are more sensible to the volume pot value you hook up than others. Especially when they have a high-ish output. A smaller value will for example load down a circuit like the Fuzz Face resulting in overall less treble and volume. A circuit using OP-amps like the tube screamer will be far less (or not at all?) influenced by the pot value, because it has a low output impedance.

Did you just say that as you turn up a fuzzface it gets bassier? I'm not trying to be a smart ass.

I think what was said is that using a lower value VR for the volume divider can result in trebble and volume loss, possibly is a fuzzfaece

indeed that's what I meant. But actually i'm not so sure anymore about the treble loss ... most threads here seem to indicate that in a Fuzz Face lower volume pot = more treble, higher = more bass ... oh well, maybe some one will chime in with a more acurate explanation ;-)

[mistahead]

Capacitance...

Its the answer.

Not sure how to apply it well here though.