Potentiometer Values...

[jishnudg]

So how does one decide the values of potentiometers used for master volume controls? I've seen values ranging from 10k to 470k ( most of them seem to be 100k)...whats the theory behind selecting a potentiometer for this?
Thanks
J.

[Thecomedian]

Standard voltage divider rules.

i modelled some stuff in LTspice. A passive tone control with far too small or too high pot distorts the way the tone control works, usually turning it into something like a flat line with a cutoff freq of either just high or low, as opposed to variable voltage over different frequencies.

The right size pot gets you the most voltage for output, and smaller pots get you less voltage. Larger pots get you more voltage.

Basic meaning behind it all. Im sure impedances of circuits behind and in front of the pot are a factor too.

[midwayfair]

A smaller pot will have lower output impedance but less output.

A larger pot will have more output but higher output impedance.

The volume pot and output capacitor combined also form a simple high-pass filter, so the value of the volume pot can determine what frequencies are passed at the output. Lowering the value of the volume pot on a fuzz face, for instance, produces a slightly brighter fuzz. You can usually roughly get the cutoff frequency with a simple calculation (http://sim.okawa-denshi.jp/en/CRhikeisan.htm).

Sometimes a larger volume pot is intentionally chosen because of its larger output impedance. Echoplex preamp-based pedals, for instance.

There are very special circumstances in which the specific value might matter for the total function of the circuit, but they are rare.

[Thecomedian]

with the opposite being true for guitar pots. higher value = brighter, no cap decoupler

[gnort_2]

if you use a potentiometer with a lower value will the signal be able to be adjusted with less of a turn of the shaft then one with higher value.

otherwise- lower value: shaft turns noticeably adjusts signal throughout entire rotation
                higher value: shaft turns noticeably adjusts signal only throughout last 1/8th or 1/16th of a turn

or is the above scenario more of a characteristic of audio/log vs linear potentiometers?


Thanks all

[Thecomedian]

If the adjustment causes a  casually noticeable large change only in certain areas of the rotation, it's logarithmic. Log = AxxKohm, Lin = BxxKohm.

It's my own opinion that choosing log or linear pots is really a choice of marketing and personal preference rather than any realistic advantage. It doesn't matter if you get 50% vol at 75% rotation and 80% vol at 90% rotation, or 50% at 50% and 80% at 80%, you're going to get the volume you want either way.