Capacitance of common volume pots

[fieldwrangler]

Folks -

Anyone measured this?

Will the Mighty Extech yield valid readings across the usual 250/500k pots?

I recently had a shocking experience with an installed hi-z pickup's resonant frequency dropping dramatically relative to its behavior on the bench and started to look into this...

Bob Palmieri

[Mike Sulzer]

Folks -

Anyone measured this?

Will the Mighty Extech yield valid readings across the usual 250/500k pots?

I recently had a shocking experience with an installed hi-z pickup's resonant frequency dropping dramatically relative to its behavior on the bench and started to look into this...

Bob Palmieri

Mine does not. I think the C is very small, and that it is not causing the shift in frequency that you see. In a low Q circuit the actual peak frequency response is a function of just how low the Q is, while the formally defined resonance frequency would not reflect that. Load with a different R and you see some shift.

[John Kolbeck]

I measured about 10pF when I hooked a quarter sized pot to my Extech. It is hard to get a good reading, because even having the probe leads near each other causes several picofarads capacitance. It looked to me like it was right about 10pF, though.

[fieldwrangler]

I measured about 10pF when I hooked a quarter sized pot to my Extech. It is hard to get a good reading, because even having the probe leads near each other causes several picofarads capacitance. It looked to me like it was right about 10pF, though.

Certainly seems about right; they don't look like very good capacitors to me!

[fieldwrangler]

Mine does not. I think the C is very small, and that it is not causing the shift in frequency that you see. In a low Q circuit the actual peak frequency response is a function of just how low the Q is, while the formally defined resonance frequency would not reflect that. Load with a different R and you see some shift.

Sounds right to me!

[J M Fahey]

The point being even if you have a 2:1 error either way because of probe capacitance, etc. , in any case we are talking VERY SMALL capacitance , I bet internal guitar wiring is higher than that, so any change you notice must be caused by something else.

[John Kolbeck]

Will the Mighty Extech yield valid readings across the usual 250/500k pots?

I recently had a shocking experience with an installed hi-z pickup's resonant frequency dropping dramatically relative to its behavior on the bench and started to look into this...

Sorry, I missed this obvious question earlier, does "on the bench" also happen to mean "without a guitar cable" by chance? Guitar cables are the major cause of resonance drop, almost without exception.

[fieldwrangler]

The point being even if you have a 2:1 error either way because of probe capacitance, etc. , in any case we are talking VERY SMALL capacitance , I bet internal guitar wiring is higher than that, so any change you notice must be caused by something else.

Thanks for this. Really, the pots seem like the most insignificant capacitive elements just by looking at them in terms of conductive area, proximity, etc. I just decided to get somewhat more specific about all this stuff instead of just "assuming" as I'm prone to do.

In fact, the shielded cables are reacting at 80 pf per foot.

[fieldwrangler]

Sorry, I missed this obvious question earlier, does "on the bench" also happen to mean "without a guitar cable" by chance? Guitar cables are the major cause of resonance drop, almost without exception.

Without doubt. Fortunately, in this application the maker supplies a specific cable for the instrument, so I get to control that factor.

In fact... anyone have some low-C well-shielded cable they like for hi-z guitar hookups??