[sdiy] Linear Taper versus Audio Taper potentiometers inquiry

[Tim Parkhurst]

On 11/25/05, Jeff Farr <moogah at gmail.com> wrote:
>
> Well, if your going to be attenuating an audio signal directly with
> the pot you need an audio taper (suprise).  If, however you are
> planning on controlling a VCA with the fader (and why not?). I believe
> you'll need linear taper.
>
> On 11/25/05, Logan Mitchell Sr <prowlerraven32 at yahoo.com> wrote:
> > 11/25/2005
> >
> > What is the difference between linear taper & audio taper
> potentiometers,
> > and which one should be used for input level controls on a multi-channel
> > mixer that's being made for a homemade analog synthesizer ? I want to
> > incorporate one in the same cabinet as the rest of the synth modules.
> >
> > Logan
> >


Audio taper pots are also used when you're controlling something like an R/C
time constant. Fer example, many ADSRs use audio taper pots for the A, D and
R times, while the Sustain level is a linear taper pot.

By the way, the difference between a linear taper and an audio taper pot is
this: a Linear taper pot has a linear change in resistance along its travel.
If you take a 100k linear pot and move it 1/4 turn, you'll get 25k
(approx.). If you move it 1/2 way, you'll get 50k, 3/4 turn and you'll get
75k. In other words, if you plotted the pot's resistance vs. its travel, the
plot would be a straight line. Now an Audio taper pot has a non-linear
change in resistance along its travel. The resistance will typically change
slowly at first, then more rapidly as the pot reaches the end of its travel.
Take a 100k audio pot and move it 1/4 turn, you might get 5k or so. 1/2 turn
gets you about 10k (approx), and 3/4 turn gets up to 30k. Most of the change
in resistance will be in the last 10 to 15% of the travel. This works okay
for audio because this is the way our ears respond to power levels. There's
a pretty good explanation, along with a graph showing a plot of the
different types of pot responses at
http://www.geofex.com/Article_Folders/potsecrets/potscret.htm


However, here's one thing that puzzled me a little, and maybe the gurus out
there can answer this one: Looking at the pot values on the ARP
Odyssey/Avatar, I see that the Fine and Coarse frequency controls for the
VCOs are linear pots. Okay, that makes sense. What puzzles me is that the CV
input pots (modulation from LFO, S/H, etc.) are audio taper.
http://www.arpodyssey.com/odyssey-slider-values.jpg
It obviously works, but I would have thought all the pots on the CV input
summer would be linear. Any thoughts or explanations?


Tim (explaining and asking at the same time) Servo
--
"Imagination is more important than knowledge." - Albert Einstein
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