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Of course, it depends a lot on the taper of the volume control.

I need to know how turning the volume knob affects signal voltage.

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  • \$\begingroup\$ You could just look for the spec you can find in pot datasheets like this one from bourns (page 3). \$\endgroup\$
    – brhans
    Jul 23 at 14:21

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Here's how I measure it.

I used:

  • an ItsyBitsy M4 microcontroller's 3V pin to provide a fixed 3.3VDC which served as a "signal",
  • a Fender S1 potentiometer as a volume control
  • the Itsy's A4 analog input to measure the voltage from the centre tap of the volume pot

I adjusted the volume control in 42 increments of approximately equal rotation (corresponding to the knurled ridges on the knob). At each increment, I measured the voltage by taking 32 readings from the A4 pin in quick succession. The graph below plots the average and range from each increment.

Note about the scale: the Itsy measures 3.3V as 65535, and 0V as 0.

I have read that some volume controls with "audio taper" use two sections of linear track, which might explain the shape seen here.

graph of measurements

Here are the raw numbers

[(160, 206.0, 256), (160, 206.0, 256), (160, 209.0, 256), (160, 209.0, 320), (160, 203.0, 288), (128, 201.0, 288), (0, 344.0, 608), (384, 920.0, 1504), (608, 1444.0, 2016), (1248, 1935.0, 2784), (1152, 2345.0, 3392), (2080, 3215.0, 4288), (2432, 3498.0, 4608), (3104, 4015.0, 5280), (2944, 4111.0, 4992), (3072, 4670.0, 5632), (3552, 4705.0, 5952), (3488, 5308.0, 6976), (4640, 5783.0, 6656), (4864, 5933.0, 7072), (5440, 6484.0, 7776), (5504, 6531.0, 7936), (5888, 7150.0, 8608), (6816, 7765.0, 8576), (7328, 8345.0, 9120), (7904, 9073.0, 10112), (9024, 10288.0, 11584), (10368, 11478.0, 12704), (11360, 12849.0, 14176), (15232, 16793.0, 18848), (19424, 21055.0, 22432), (24096, 25076.0, 26080), (28576, 29744.0, 31168), (32864, 33939.0, 35008), (37440, 38750.0, 40032), (41952, 43124.0, 44032), (46880, 47782.0, 48640), (52288, 53667.0, 54528), (57696, 58692.0, 59616), (65520, 65520.0, 65520), (65520, 65520.0, 65520), (65520, 65520.0, 65520), (65520, 65520.0, 65520)]

Here's my experimental setup experimental setup

Here's a close-up of the volume control, showing the knurls which determined the increments potentiometer

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