"RA" taper?

[H4T]

I want to build an EA Tremolo, but one of the pots is listed as being an "RA" taper. Does this mean "reverse audio," and if so, can I just wire up a regular audio taper pot backwards? Otherwise, what do I ACTUALLY use here?

p.s., I'm referring to the Rate pot, info at: http://runoffgroove.com/eatremolo.html

[snoof]

reverse audio refers to the taper of the pot, not the rotation.

[Mark Hammer]

I want to build an EA Tremolo, but one of the pots is listed as being an "RA" taper. Does this mean "reverse audio," and if so, can I just wire up a regular audio taper pot backwards?

Yes.  On an audio taper pot, resistance from wiper to "input" lug increases logarithmically as you rotate clockwise.  If you were measuring from the wiper to the opposite side lug, resistance would increase logarithmically as you rotated counterclockwise.

Normally, in a log taper, the requirement is for resistance change per degree rotation to increase as you go clockwise. There ARE some circuits where the rate of change needed to achieve suitable "dialability" requires that you go through a lot of change in resistance very quickly and then simmer down to smaller amounts of resistance change.  One case in point is the Drive pot on an MXR Distortion+ where you have to scoot through some 900k of resistance before you start to achieve noticeable changes in gain.  The last 50-100k of resistance change gets you all the interesting differences in gain, so the required taper of the pot is one that stretches out that last 5-10% of total resistance over a big chunk of the pot's rotation.  That pot is reverse audio, reverse log, or "antilog".

Of course, all of this need for reverse tapers is predicated on the assumption that you absolutely need to be able to dial in "more" of something by specifically going in a clockwise direction.  If you were fine with wiring up a regular log taper pot in reverse and having the 5:00 position be "slower", as opposed to "faster", then you're good to go.  There are a lot of things where it messes with your head to have "less" as you rotate clockwise, but happily there are plenty where the mental translation is easy to do.  "Slower" would appear to be one of those.  Perhaps because it is easy to imagine stepping harder on the brakes as a kind of "more".

[jlullo]

mark,
that's good to know! now i'm not going to bother ordering a RA taper pot for my EA trem

jonathan