Potentiometers for Fender Amplifiers
Note: A pot is
guitar pots have a layer of conductive carbon deposited on a
phenolic plastic base. A metal "wiper" sweeps along this carbon
resistance path as the pot shaft is rotated, allowing us to change the
resistance and thus choose the level of attenuation. The density
of the carbon deposit determines the taper of the pot. A linear taper
changes resistance evenly; at about half rotation (12 o'clock) you'll
roughly half the total resistance of the pot. An audio (A.K.A.
taper pot works differently; you'll have to turn it up to about three
rotation to measure one half of the resistance value of the pot. Try
yourself with an audio taper pot, a linear taper pot and an ohm meter.
Looking down at the top of the pot with the solder lugs facing away
you, put your two meter probes on the left-most and center solder lug.
Now turn the pot all the way counterclockwise and you should measure
total resistance of the pot (e.g. 500K or so...). Now turn the pot
clockwise to about half rotation; it helps to have a pointer type knob
on the shaft to keep track of the rotation. If you're measuring a
taper pot, about half rotation should give you half of the total value
of the pot. If you turn this linear taper pot up about three quarters
you'll measure 20-25% of the total resistance value. When you turn the
pot up all the way clockwise you will probably still measure some
say 2 to 60 or so ohms. Now try to measure an audio pot. You find that
the resistance changes only 15-20% or so at half rotation, reading half
the total resistance value only after you've reached almost three
rotation and then it drops rapidly (logarithmically...). Audio taper
are commonly used when fine adjustment is needed at lower listening
There are many other pot tapers available. In my experience, different
examples of even" standard" tapers such as "audio" can vary quite a bit
in how they feel to a guitarist. Here again, experimentation with
pots may be worthwhile. Remember that a pot is not an amplifier; it can
only attenuate signal.