# Exponential potentiometer

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#### argo

Does anybody have an idea how to make exponential potentiometer from linear or logarithmic pot using resistor(s) a la Rod Elliot’s “better volume control”?

Argo

#### AudioFreak

Why do you want an exponential volume pot? Human hearing operates in a logarithmic manner ... exponential is the oposite to logarithmic and so would result in an even worse volume control than a standard linear pot...

Rod's project creates an approximation of a true logarithmic pot (almost all 'log' pots sold these days are linear log not truly logarithmic) over a relatively small range (about 20dB)

#### TG

Hello argo,

You can do this with a linear pot by adding resistor between input and output pins (not between ground and output, as it's done by Rod Elliot). The value of this resistor should be 0.3-0.5 of initial pot value.

Good luck!!!

#### argo

AudioFreak said:
Why do you want an exponential volume pot? Human hearing operates in a logarithmic manner ... exponential is the oposite to logarithmic and so would result in an even worse volume control than a standard linear pot...

.. You are right but I don’t need that pot for volume control but for phase control. I just mentioned Rod's project because he uses simple risistor to turn linear curve into to logarithmic. So I thought one can do vice versa to produce exponential curve.

Argo

#### AudioFreak

ok now i understand your point

#### argo

Thanks TG, I tried that already ...maybe there is something wrong with simulation soft I have but it seems this doesn’t work either. ...or maybe because the pot doesn’t have direct connection to ground?

Argo

#### TG

Yes, this method assumes direct connection to the ground...

If you need totally "floating" pot, it won't work.
And I'm afraid you need true exponential pot for this...

#### JDeV

Log or Linear?

For volume control purposes, will a Log pot always be the best option? What are the audible differance between a Log and Lin pot?

#### Havoc

There are no "audible" differences between lin and log, but it is much more comfortable to use a log. It feels more right.

With a lin you would use only a small part of the turn range and it would be sort of compressed at one end. You turn it, and to make it twice as loud, you only have to turn it now half so far further. Twice as loud, again half so far (1/4 of the initial turn).

The log gives a more spread out use. Like if you turn it twice as far, it sounds twice as loud.

#### Pjotr

Quite right Havoc. But log tapers can suffer from large deviations between left and right channel. Especially at low volume settings. Log tapers are usually –20 dB halfway. A linear pot with a resistor parallel from taper to ground can mimic a log taper for volume control quite satisfactory. As a general rule this resistor need to be approx. 1/16 of the resistance value of the pot. This gave me satisfactory results and the same “feeling” of a regular log pot and synchronisation between left and right is far more accurate. However the driving stage must be capable of driving the total lower resistance without problems. “Full open” is sees approx. 1/20 of the normal resistance of the pot.

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