really weird linear potentiometers that have a logarithmic response

VvvvvV · 13th February 2007, 03:39 PM

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?

Daveze · 15th February 2007, 10:58 AM

Because sound pressure/volume is usually a log scale?

VvvvvV · 17th February 2007, 07:33 PM

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.

Nigel Goodwin · 17th February 2007, 08:49 PM

Obviously the original pot wasn't linear then, it was either log, anti-log, or some special custom pot (less likely).

uhcmos · 21st February 2007, 01:09 PM

thanks

VvvvvV · 5th March 2007, 12:24 PM

thanks for that

sreten · 5th March 2007, 05:12 PM

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.

Albertb · 10th March 2007, 05:57 PM

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

VvvvvV · 30th March 2007, 10:00 PM

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

13th February 2007, 03:39 PM	#1
VvvvvV diyAudio Member Join Date: Oct 2003 Location: oxfrd	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?

15th February 2007, 10:58 AM	#2
Daveze diyAudio Member Join Date: Jun 2004 Location: Sunny Queensland, Australia	Because sound pressure/volume is usually a log scale? __________________ Signature Pending...

17th February 2007, 08:49 PM	#4
Nigel Goodwin diyAudio Member Join Date: Jul 2005 Location: North Derbyshire	Obviously the original pot wasn't linear then, it was either log, anti-log, or some special custom pot (less likely). __________________ Nigel Goodwin

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17th February 2007, 07:33 PM	#3
VvvvvV diyAudio Member Join Date: Oct 2003 Location: oxfrd	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.

21st February 2007, 01:09 PM	#5
uhcmos Banned Join Date: Feb 2007 Location: CHINA	thanks

5th March 2007, 12:24 PM	#6
VvvvvV diyAudio Member Join Date: Oct 2003 Location: oxfrd	thanks for that

10th March 2007, 05:57 PM	#8
Albertb diyAudio Member Join Date: Apr 2006 Location: Hants	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

30th March 2007, 10:00 PM	#9
VvvvvV diyAudio Member Join Date: Oct 2003 Location: oxfrd	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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