Potentiometer prefix - A, B, C?

[YurkshireLad]

I'm looking for some potentiometers and I noticed that the various values are prefixed by A, B or C. Is there any significance to these letters or do I only concern myself with the resistor's value?

[davent]

Prefixes refer to the taper, A - audio/log, B - linear, C - inverse audio/log. Audio taper resistance slowly increases between wiper and ground as the knobs turned clockwise until the knee where-after it hits max resistance in hurry, linear, steady flat increase in resistance throughout the travel, inverse audio self explanatory.

[Rob Strand]

They represent the pot taper, go down just past half way to Marking Codes,
https://eepower.com/resistor-guide/resistor-types/potentiometer/

The common types are the Japanese/American codes.   The Japanese types also have C (and G).

Unfortunately there are other marking codes in *every country*.   It's bit of a pain but generally you
assume the common Japanese/American codes.

[YurkshireLad]

Ah thanks! I tried searching but I didn't hit the right keywords. So A is best for guitar pedals?

[davent]

Ah thanks! I tried searching but I didn't hit the right keywords. So A is best for guitar pedals?

They'll all get used but most common are audio and linear, depends on what function they are controlling.

[idy]

What are you thinking of building? I try to keep A and B taper. There are some well known pedals that use C. MXR Distortion +...

And a few that use an A taper wired backwards ("more" CCW, "less" CW) to avoid using a C.

[YurkshireLad]

Im looking for pots for the volume and gain controls for a distortion pedal.

[GibsonGM]

Audio taper for volume pots. But linear will work for testing and 'learning'....the audio taper gives a smoother, more natural response. Human hearing is logarithmic, so linear control seems 'bunched up' to one end of the pot travel. 

Gain is generally "B", or linear, taper.    Values of 10k, 100k and 1meg are VERY common for each 'type'.

[Mark Hammer]

The preferred taper will depend on where one wants/needs the most differentiation to be.  Any pot of the right resistance value will "work", but the user may find that the control will be twitchy, and magical settings hard to replicate.  This will probably be more true of smaller diameter pots (9mm vs 12 vs 16mm vs 24mm), where the circumference of the resistive strip is much shorter, and the contact made by the wiper less precise.

So, for instance, when it comes to LFO "speed" control, reverse-log (C taper) is generally preferred, since it allows one to "skip through" the slowest rates easily, and have finer gradations in faster speeds available over most of the rotation of the control.  Of course, that presumes that clockwise = "faster".  If one doesn't have reverse-log available, you simply use regular A-taper log, and wire the pot "backwards", such that clockwise = slower.

Reverse-log can have other applications beyond LFO rate.  For example, the MXR Distortion+ used a C-taper pot for Distortion intensity. Why?  My own hypothesis is that, at the time, simply boosters, apart from the EHX LPB-1, were rare.  The use of a large-value C-taper pot allowed the user to dial in lower-gain boosts that would not be clipped by the diodes, and easily skip past those clean-ish settings to dial in gradations of grind.

Personally, I wish I could find a 1M W-taper pot with a centre-detente.  W-taper is a sort of blend of linear and log, with logarithmic change in each direction from the midpoint.  Generally used for symmetrical boost/cut on EQs.  One CAN also use linear pots, but the feel of the adjustment on W-taper is more pleasing to the user. 

I like to use a "bi-directional" tone control on my guitars, providing one treble cut in one direction, and a different one in the other direction.  Since guitar tone controls are never out-of-circuit (unless treated to be "no load"), a 1M pot of this type, set to its midpoint, is essentially two 500k pots in parallel, which is a sort of 250k resistance to ground through several caps.  Hence the use of 1M where one is normally used to a much lower pot value for tone control.