[AMRadio] LOG, LINEAR, and REV LOG


Bob Bruhns 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.

   Bacon, WA3WDR


More information about the AMRadio mailing list

This page last updated 15 Dec 2017.