really weird linear potentiometers that have a logarithmic response - diyAudio
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Old 13th February 2007, 03:39 PM   #1
VvvvvV is offline VvvvvV  United Kingdom
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Default really weird linear potentiometers that have a logarithmic response

I bought a bunch of linear potentiometers and I have measured them they look totally linear in all measurements, but when I attached them to a novation commercial circuit board and controlled a music program the response of the knob in the software was completely logarithmic started very slowly and went fast at the end...

that is really really weird because it means that the Novation circuit board uses logarithmic potentiometers that are converted into a linear signal which is just completely barmy. so when I attach a linear one it's converted to a logarithmic signal.

Why the hell would this insane thing happened that a manufacturer uses logarithmic potentiometers converted into a linear MIDI signal?
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Old 15th February 2007, 10:58 AM   #2
Daveze is offline Daveze  Australia
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Because sound pressure/volume is usually a log scale?
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Old 17th February 2007, 07:33 PM   #3
VvvvvV is offline VvvvvV  United Kingdom
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yes but i'm plugging in a linear potentiometer into a linear MIDI controller and the results coming out of the MIDI controller is logarithmic compared to the original potentiometer.
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Old 17th February 2007, 08:49 PM   #4
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Obviously the original pot wasn't linear then, it was either log, anti-log, or some special custom pot (less likely).
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Old 21st February 2007, 01:09 PM   #5
uhcmos is offline uhcmos  China
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thanks
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Old 5th March 2007, 12:24 PM   #6
VvvvvV is offline VvvvvV  United Kingdom
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thanks for that
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Old 5th March 2007, 05:12 PM   #7
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by Nigel Goodwin
Obviously the original pot wasn't linear then, it was either
log, anti-log, or some special custom pot (less likely).
Hi,

This does not follow at all, completely depends on the crcuit its connected to, /sreten.
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Old 10th March 2007, 05:57 PM   #8
Albertb is offline Albertb  United Kingdom
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It depends what impedance you are putting it in with. Not only the value but the shape of any pot can be altered by hanging other resistances around it. A resistor between the top or bottom and the wiper for example will have a very profound effect. Could be as simple as that!

You could check out its action very roughly out of the circuit with a DC source, (9v ish battery?), and a meter. Make sure that any impedances in the circuit around the pot are much larger than its own value to minimise their effect on it
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Old 30th March 2007, 10:00 PM   #9
VvvvvV is offline VvvvvV  United Kingdom
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thank you for that excellent advice, I thought that all 10k potentiometers would be the same, other than the curve, perhaps the circuit is going around the potentiometer so I should try and isolate one for measurements, and I will try and figure out what's going on with the voltage and impedance- it sounds like it takes a lot of thinking
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