Friday 13 December 2019

Potentiometers - convert Linear to Log

Converting the linear potentiometers to log pots.

This may come in handy if you don't have the appropriate Audio/Log pot at hand (because of an odd form factor or dual pot configurations), or if you wish to tailor the log curve.

Usually the three lugs or terminals are numbered:
1. input
2. Wiper
3. Ground

The usual solution is to add a resistor between the pot wiper & ground. If you can pick the right size, the result will be
close to a logarithmic response. This is usually OK for most audio applications. You don't have to stop there. Fixed resistors can be added to both ends. .... ie between the input & wiper, and ground & wiper.

The results can be wonderful ... or crazy.
It's all about taper.
1. Reverse Log / Reverse Audio (A)
2. Linear Taper (B)
3. Logarithmic Audio Taper (A)
4. Straight line "pseudo-audio" taper

Usually a resistor value of 10% to 20% of the pot resistance gives a good approximation of an audio-taper pot.
Smaller values will give less change in volume at the lower portion of pot rotation, higher values will give more change.

This is a dual gang pot.

This is a 1M reverse log pot.
It's marked C1M

1 comment:

  1. So, being A or C type is determined by the lugs used to connect a parallel resistor ?