6G8 bass potentiometer

[deci belle]

The schematic for the Fender Brown (blonde) Twin amp says the bass pot is a 1Meg-D.

I've seen A, L, and RA pots, but what does the D mean?

How is that different from a 1Meg-A pot?

[Jazz P Bass]

'D' is a log taper.

At 50% travel, you will read 10% of the overall value.

Pro Audio Reference P

[g1]

If there are actually pots designated as "L", would that signify linear or log?

[deci belle]

And thanks for the link too, Jazz!

The taper defines the amount of resistive change as a function of travel. Several popular examples follow:
audio taper (aka A-taper): Usually 15% resistance at the 50% rotation point.
C-taper: usually a reversed audio taper.
E-taper: Similar to a reversed audio taper but with 25% resistance at the 50% rotation point.
linear taper (aka B-taper): Always 50% resistance at the 50% travel point.
log taper (aka D-taper): Often used as an audio taper since its 50% rotation point has 10% resistance.
MN taper (aka balance pot): Special taper developed for home stereo "Balance" controls. Consists of two sections (one for each channel) operating opposite each other. Exactly one-half of each section is a zero resistance surface (i.e., solid-copper or equivalent), the next 50% of travel is linear taper. Therefore for one channel rotating the slider through the first 50% of travel does not change the level at all, while the other channel is reduce from full to zero, and vice versa, with the middle position (usually featuring a center-detent) always passing full signal to each channel. See balance control.
RD-taper: A reversed D-taper (see log taper above).
W-taper: A modified linear taper with the standard 50% resistance at the 50% travel point but is must steeper on both sides, then slows down above and below the 85% and 15% points. A special version is used for the boost/cut control found on analog equalizers. This version adds a dead zone in the middle, which is fitted with a center-tap terminal that is usually grounded by the application so that the center position has no effect on the assigned frequency band.

What g-one said …so Linear (B-taper) is 50% at 1//2 turn.

[pdf64]

Just to note that those designations aren't a worldwide standard, eg from Omeg P20 potentiometer data
Resistance Laws (Taper) - A (Linear), B (Audio/Log), C (Reverse Audio/Anti Log)
Pete

[deci belle]

That link puts the tapers on graphs— with a lot of information too. Thanks Pete!

[wyatt]

Just to note that those designations aren't a worldwide standard, eg from Omeg P20 potentiometer data
Resistance Laws (Taper) - A (Linear), B (Audio/Log), C (Reverse Audio/Anti Log)
Pete

That's the modern standard that most companies now use, especially since they've streamlined their industrial offerings. In the '80's, the MBA's took over and wide catalog offerings where whittled down to a handful of compromises, and everything else is a large-quantity custom order.

But if you run into a 30+ year old pot, there's a good bet it uses A=Audio, B=Linear, C=Rev Audio, and D=Log. But few of us deal with those except to repair.

[pdf64]

'But if you run into a 30+ year old pot, there's a good bet it uses A=Audio...'
Yes if it's USA etc manufacture but my understanding is that UK made log pots, where such a code is used, have generally always been 'B', linear 'A'.
Pete