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23rd May 2002, 12:05 PM  #1 
diyAudio Member
Join Date: Feb 2001
Location: Estonia

Exponential potentiometer
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 
23rd May 2002, 12:23 PM  #2 
Warp Engineer
On Holiday

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) 
23rd May 2002, 12:28 PM  #3 
diyAudio Member

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 0.30.5 of initial pot value. Good luck!!! 
23rd May 2002, 12:35 PM  #4 
diyAudio Member
Join Date: Feb 2001
Location: Estonia

[QUOTE]Originally posted by AudioFreak
[B]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 
23rd May 2002, 12:49 PM  #5 
Warp Engineer
On Holiday

ok now i understand your point

23rd May 2002, 12:55 PM  #6 
diyAudio Member
Join Date: Feb 2001
Location: Estonia

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 
23rd May 2002, 01:15 PM  #7 
diyAudio Member

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... 
28th November 2002, 01:38 PM  #8 
diyAudio Member
Join Date: Oct 2002
Location: Cornwall

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?
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28th November 2002, 05:17 PM  #9 
diyAudio Member
Join Date: Feb 2002
Location: Belgium

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. 
28th November 2002, 10:41 PM  #10 
diyAudio Member
Join Date: Nov 2002
Location: Netherlands

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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