# Convert log pots to linear pots

Discussion in 'Electronic Basics' started by [email protected], Dec 11, 2006.

1. ### Guest

Hi,
I am getting log pots (audio pots) very cheap. Is there a way to
convert this to linear ones?

I've seen a few designs on the net that convert linear to logarithmic
by adding a resistance or two, but not any for the other way round. Is
this doable by similarly connecting a resistance?

Thanks,
Venkat.

2. ### Bob MyersGuest

In short, no. If you want linear, buy linear.

Bob M.

3. ### Don BruderGuest

Not that I've ever heard of. Adding resistances to convert linear to log
is pretty easy, but as far as I'm aware, converting log to linear would
require physically reworking the resistance element of the pot. Dunno
about you, but that's a task that's *WELL* beyond my skill... (Well, OK,
maybe not "beyond" - I'm sure I could hack on a pot and alter its
performance, but I wouldn't count on the results being anywhere near
reproducible or predictable, which probably eliminates any usefulness...)

4. ### BobGGuest

If you are gettin em for half price, hook 2 of em up back to back to
cancel each other out.

5. ### kellGuest

It probably won't come out perfectly linear, but you could straighten
it out some by attaching a resistor to the wiper and one of the legs.
experiment. Let us know what happens.

6. ### Michael BlackGuest

How?

On a linear pot, each degree of rotation of the shaft has an equal resistance
change. On a log pot, that change of resistance per degree of shaft
rotation varies.

You can "syntheisze" a log pot with a resistor from the arm to one of
the fixed ends (for discussion, we'll assume the ground end) of the pot
because that resistor will be swamped out as the arm gets closer to ground
(where the resistance from the arm to ground becomes less). Move
the arm up towards the free end, and the resistor from the arm to ground
will have more of an effect on the resistance of the pot.

But if add a resistor to a log pot, as the poster is asking, you will
get the same effect, only magnified. Not only will the pot be logarthmic,
but the resistor will add to the effect.

Michael

7. ### kellGuest

Listen, I know he's not going to get a true linear pot but he can fake
it.

Set the log pot at its physical midpoint. Take resistance measurements
from the wiper to the endpoints of the pot, call them R1 and R2. Get a
resistor with a value approximately equal to the absolute value of
R1R2/(R2-R1). Connect this resistor between the wiper and the end of
the pot where you measured the higher resistance, you now have a pot
with a resistance centered at its physical midpoint.

Yes, probably crappy. But what's the harm? If the guy wants to take
log pots and try to "convert" them, let him.