"J" taper vs. "A" taper pots.

[J M Fahey]

Look what the cat brought: from a post in diy Audio :

https://www.vishay.com/docs/51031/p11sp11a.pdf

Vishay pot datasheet, including what they call pot tapers.

To add to the general confusion:

* A is Linear

* L is 10% Log

* W is 20% Log

* F is 90% antiLog

* S is S , 10% Log plus 90% anti Log in the same track

* R is 10% Log but with pin contacts reversed, wiper apparently touching a contact is actually farthest from it.

Another IMPORTANT parameter nobody quotes and which is VITAL, literally, is track to body insulation and dielectric strength: IMPRESSIVE 1500VAC RMS (I am floored by that), good for those making Tube Amp PPIMV and specially MosFet Power Attenuators.
It simplifies their life very much-

[Helmholtz]

A is Linear

That's the old German (European?) nomenclature.

Vishay acquired several German pot and resistor manufacturers (Roederstein, Draloric, Beyschlag..). Seems they continue to use their original taper designations.

[pdf64]

To my knowledge, ‘A = linear’ has always been the standard for UK manufacturers too, eg see p3 of https://www.omeg.co.uk/wp-content/up...0BU-B4OW2S.pdf

[Helmholtz]

To my knowledge, ‘A = linear’ has always been the standard for UK manufacturers too, eg see p3 of https://www.omeg.co.uk/wp-content/up...0BU-B4OW2S.pdf

Most interestingly they also use the German termination terminology:
A: Anfang (start)
S: Schleifer (wiper)
E: Ende (end).

[pdf64]

Most interestingly they also use the German termination terminology:
A: Anfang (start)
S: Schleifer (wiper)
E: Ende (end).

I'd never have worked that out for myself, thanks!
Omeg will build custom pots, from their FAQ If the model selected consists of parts already in existence then the minimum order quantity is 10 pieces and the minimum order value is £25 + carriage + VAT if applicable.

[Chuck H]

One thing I want to say on the matter. It's just as Juan has described in an earlier post. Any ideal that the log tapers are curved in any way is a fantasy. Example: for a 10% log pot It's a straight (ish) line through the 10% margin at five that continues to just past six before intersecting another straight (ish) line to it's final resistance pad somewhere between nine and ten (it's pretty sloppy actually). The curves shown by, say, Alpha that look to have anomalies in the curves that are still close enough to best practice ARE F#@&!nG CARTOONS!!! If you're ever designing something that's dependent on the pot curve in question (and sensitive to it) you absolutely should buy several examples of that pot and test them yourself on your own bench. I probably wasted over two hundred hours working with the published taper curves while doing cad design and simulations. Even Bourns and CTS are guilty. The taper curves shown are made up for marketing purposes. Really. When it actually matters you must purchase the product in question and take your own measurements because the manufacturers published taper curves are quite literally lies.

[Gregg]

Any ideal that the log tapers are curved in any way is a fantasy. Example: for a 10% log pot It's a straight (ish) line through the 10% margin at five that continues to just past six before intersecting another straight (ish) line to it's final resistance pad somewhere between nine and ten (it's pretty sloppy actually).

This is entirely true. Below is an interesting article about tapers of some well known HiFi pots together with an Excel table with graphs:

https://tangentsoft.net/audio/atten.html

I also have this graph of several commonly used pots measured according to the article (the yellow line is an ideal 10% taper also according to that formula) which only confirms what was said about the real life log tapers.