|[AMRadio] LOG, LINEAR, and REV LOG|
bbruhns at erols.com
Thu Sep 6 17:42:21 EDT 2007
Fortunately we seldom encounter anything but linear or log or audio tapers, but I have seen reverse-log pots being sold. Log taper
seems to be considered different from audio taper - maybe audio taper is not as precise.
I once had an audio mixing board that had linear sliders!!! Arrrgh, real mixing was very difficult that way.
It was the age before the internet, and I had trouble finding physically compatible replacements. But the circuitry driving the
pots was low enough Z, so I added a fixed resistance from each wiper to ground The pots were about 50K, and I added something like
2.2Kfrom the wiper to the ground end. What that did was it caused the middle of the adjustment range to sag down in level, making
the control a lot more like audio taper.
It was still tricky, though. You want a certain rotation angle, or a certain slider distance, to produce a certain perceived volume
change. All the extra resistor did was improve a terrible situation. If I'd had more money and time, it would have been better to
find audio taper sliders of higher quality.
I suppose an audio taper pot could behave more like a linear taper by using the reverse of that trick - adding a resistor from the
wiper to the high side. But the resistance would change with the pot setting.
Another trick: my R392 had less high frequency response with its volume control set in the middle, because of stray capacitance in
the line from the wiper to the audio amp. I added a small cap from the high side of the pot to the wiper to compensate.
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