Arrggh..I can NEVER keep this straight!

[Fred G.]

I've got a few brand new Alpha pots I bought several years ago sitting in a drawer, but they're marked as the pot value with a 'B', i.e., B250K, B1Meg, etc.

Are these audio or linear taper pots? I can't remember! I have others clearly stamped "audio".

What confuses me even further is when I look at the Duncan tone stack calculator and see as pot options "linear", "Log A", and "log B".

Will some kindly soul please straighten me out (again)?

Thanks in advance,

Fred G.

[Don Symes]

Set the wiper to 50% rotation.

Is the value 50% (of the end-to-end measured value)? Yes - linear, no - some audio taper ( I think the %value at 50% rotation is the log percentage ... and I think I remember that Log A is 10% and log B is 20%.)

[Mark Black]

"B" on an Alpha pot pretty much guarantees linear.

[Jag]

From http://www.patent-invent.com/electri...ntiometer.html

Linear potentiometers
A linear law pot ("type B") has a resistive element of constant cross-section, resulting in a device where the resistance between the wiper and one end terminal is proportional to the distance between them. Linear describes the electrical 'law' of the device, not the geometry of the resistive element.


Logarithmic potentiometers
A log pot ("type A") (sometimes called a log taper pot) has a resistive element that either 'tapers' in a logarithmic manner from one end to the other, or is made from a material whose resistivity varies logarithmically from one end to the other. This results in a device where the distance between the wiper and one end terminal is proportional to the logarithm of the resistance between them. The 'log pot' is used as the volume control in audio amplifiers, where it is also called an "audio taper pot", because the amplitude response of the human ear is also logarithmic. It ensures that, on a volume control marked 0 to 10, for example, a setting of 5 sounds half as loud as a setting of 10. There is also an anti-log pot or reverse audio taper ("type C") which is simply the reverse of a log pot. It is almost always used in a ganged configuration with a log pot, for instance, in an audio balance control.

[Bruce / Mission Amps]

What's wrong with all this is that it seems like many modern made audio pots are not log or audio.
They act like a series string of 5 or 6 non-linear straight taper resistances with knees or bumps in the resistance.
I've wondered many times if that is what is ment by log a or log b.

[Fred G.]

Thanks, everybody!

I think I'm straightened out now.

Fred G.