Volume pots: Why are low values better?

[Christer]

It is often claimed that volume pots should be of fairly low value, rather 10 k than 50 k (not considering law faking now). However, I can't remember ever reading a motivation for this claim. I can think of two reasons:

1) Noise:
Nothing to argue about there, in cases where the extra few dBs matter.

2) Avoiding unnecessary HF roll off due to cable capacitance and other stray capacitance:
Doesn't really require a low value pot since we could put a resistor in parallel with it to reduce input impedance. It may matter though in combination with input transistor capacitance.

So my question is, are these the reasons for the claim, or is there some other reason I have overlooked, or are high value pots usually of inferior quality for some reason?

[moamps]

Originally posted by Christer
...Doesn't really require a low value pot since we could put a resistor in parallel with it to reduce input impedance....

Can you elaborate please?

[Christer]

Originally posted by moamps


Can you elaborate please?

Well if I have a 50 k volume pot, the input impedance is 50 k. Connecting a resistor in parallel with the pot (between the ends, not the wiper), will make the pot appear as a lower resistance to the source.

Of course one could use a lower value pot for a start, but I can think of several reasons not to. One might already have a good 50 k pot at hand, or if investing in an expensive pot one might want to try it in different circuits, some of them requiring the higher value. One could also imagine a case where some sources demand a higher impedance. Then one could have a paralleling resistor on the other inputs, before the input selector, of course.

[audionut]

years ago there was an article in Audio Amateur on a 2k stepped attenuator...which I acrually built and am using...

In that article is explained why you might want a lower ohm volume control. Can't remember the reasons at the moment...

[Christer]

2 k is extremely lowish. Of course there is nothing wrong at all with such a low impedance, if you know your source can handle it. However, many sources will most likely not like such low loads. Even if if they often have a series output resistor on the order of 1 k to protect them from short circuits, drive capability is probably bad in most cases, causing unnecessary distorsion.

[jeff mai]

In a situation where the source impedance allows it, try a 600 ohm attenuator. Listen and you will immediately know a reason to prefer it over a 50Kohm attenuator.

[Christer]

Originally posted by jeff mai
In a situation where the source impedance allows it, try a 600 ohm attenuator. Listen and you will immediately know a reason to prefer it over a 50Kohm attenuator.

Few sources can handle that out of the box, although one could redesign them, of course. I know our two Pavels use output buffers and 50 Ohm termination at the receivng end, and claim that to improve the sound, althought they have no explanation for why.

However, although listening impressions are interesting, I would like to know why, and it it is only under certain circumstances? However, one part of my question was also if it is only the input impedance per se that matters, or if higher value pots are inherently inferior for some reason?

[Tube_Dude]

Originally posted by Christer
However, one part of my question was also if it is only the input impedance per se that matters, or if higher value pots are inherently inferior for some reason?

Hi Christer

For me is the output impedance of the pot that matters.

For ex. a 50 K pot have a worst case output impedance of 12.5K and a 10k pot only 2.5K...What a difference..

[Christer]

Originally posted by Tube_Dude


Hi Christer

For me is the output impedance of the pot that matters.

For ex. a 50 K pot have a worst case output impedance of 12.5K and a 10k pot only 2.5K...What a difference..

Sure, I agree, but if that is a problem dependes on what comes after it. If noise is not a major concern and capacitances are not too big, then it need not be a problem. I am absolutely not suggesting that a high value pot should always work fine.

[Tube_Dude]

Originally posted by Christer


Sure, I agree, but if that is a problem dependes on what comes after it. If noise is not a major concern and capacitances are not too big, then it need not be a problem.

In that case I agree with you.