Log fake resistor vs. log pot: Which is better?

Spasticteapot · 21st December 2009, 10:47 PM

I'm going to be putting in an order from Mouser, and was hoping someone could recommend some cheap potentiometers that aren't too awful. From what I've heard, sub-$5 log pots are generally pretty nonlinear, and you're better off buying a linear-taper pot and applying a log fake resistor. What do folks here recommend?

Don Hills · 21st December 2009, 10:56 PM

Check out these sites:

ESP - A Better Volume Control

http://www.elby-designs.com/document...ionometers.pdf

Spasticteapot · 22nd December 2009, 02:35 AM

The main problems I see with log-fake reistors is that they drastically alter the input impedance of the device depending on their position. Beyond adding an op-amp, how would you suggest compensating for this?

rdf · 22nd December 2009, 02:55 AM

If you have a ten-turn linear sitting around give it a try and see if you really need a logarithmic. The gain structure of your system might be such that it's rarely turned up past the first rotation. I lived for almost 15 years with twin 10K pots, only going to an active pre with 100K to make my tube phono happier.

Spasticteapot · 22nd December 2009, 02:57 AM

I guess log-fake it is.

Can anyone recommend a cheap ($2) pot from Mouser? Much more than that and I'm tempted to use one of those $15 eBay 21-step attenuators.

Glowbug · 22nd December 2009, 08:35 PM

The PEC carbon pots are supposed to be pretty good (they were used in the commercial version of the Pass B1 buffer, IIRC)...Apexjr has them for cheap, although I think you have to contact him to find out exactly what values he has.

When I finally get around to putting together my line stage, I think I'm going with two of those.

oshifis · 27th December 2009, 12:02 PM

I use a 2x100k PEC carbon linear pot and 10k law faking resistors at the tapers to ground. The problem is that the resistor does not convert the linear to a perfect logarithmic, I mean the lower 20% and the upper 20% is unusable (lower end is too loud, volume does not change much in these regions). The usable range in the middle is about 25-30 dB at most, which is not enough. I tried with different law faking resistors, neither was better.

paulb · 02:05 PM

The Panasonic EVJ from Digikey are not too bad.
Digi-Key - P2T3103-ND (Manufacturer - EVJ-C20F02A14)
Also have a look at this:
Notes on Audio Attenuators
He sells pots too; maybe the cheap Alps one would work for you:
http://tangentsoft.net/shop/

21st December 2009, 10:47 PM	#1
Spasticteapot diyAudio Member Join Date: Jan 2006 Location: Wisconsin....what did you expect?	Log fake resistor vs. log pot: Which is better? I'm going to be putting in an order from Mouser, and was hoping someone could recommend some cheap potentiometers that aren't too awful. From what I've heard, sub-$5 log pots are generally pretty nonlinear, and you're better off buying a linear-taper pot and applying a log fake resistor. What do folks here recommend?

22nd December 2009, 02:55 AM	#4
rdf diyAudio Member Join Date: Jun 2004 Location: big smoke	If you have a ten-turn linear sitting around give it a try and see if you really need a logarithmic. The gain structure of your system might be such that it's rarely turned up past the first rotation. I lived for almost 15 years with twin 10K pots, only going to an active pre with 100K to make my tube phono happier. __________________ Ears aren't microphones.

22nd December 2009, 08:35 PM	#6
Glowbug diyAudio Member Join Date: Feb 2006 Location: Hillsborough, NC/McLean, VA	The PEC carbon pots are supposed to be pretty good (they were used in the commercial version of the Pass B1 buffer, IIRC)...Apexjr has them for cheap, although I think you have to contact him to find out exactly what values he has. When I finally get around to putting together my line stage, I think I'm going with two of those. __________________ Jim J.

27th December 2009, 02:02 PM	#8
paulb diyAudio Member Join Date: Jun 2001 Location: Calgary	The Panasonic EVJ from Digikey are not too bad. Digi-Key - P2T3103-ND (Manufacturer - EVJ-C20F02A14) Also have a look at this: Notes on Audio Attenuators He sells pots too; maybe the cheap Alps one would work for you: http://tangentsoft.net/shop/ Last edited by paulb; 27th December 2009 at 02:05 PM.

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21st December 2009, 10:56 PM	#2
Don Hills diyAudio Member Join Date: May 2009 Location: Wellington	Check out these sites: ESP - A Better Volume Control http://www.elby-designs.com/document...ionometers.pdf

22nd December 2009, 02:35 AM	#3
Spasticteapot diyAudio Member Join Date: Jan 2006 Location: Wisconsin....what did you expect?	The main problems I see with log-fake reistors is that they drastically alter the input impedance of the device depending on their position. Beyond adding an op-amp, how would you suggest compensating for this?

22nd December 2009, 02:57 AM	#5
Spasticteapot diyAudio Member Join Date: Jan 2006 Location: Wisconsin....what did you expect?	I guess log-fake it is. Can anyone recommend a cheap ($2) pot from Mouser? Much more than that and I'm tempted to use one of those $15 eBay 21-step attenuators.

27th December 2009, 12:02 PM	#7
oshifis diyAudio Member Join Date: Mar 2004 Location: Budapest, Hungary	I use a 2x100k PEC carbon linear pot and 10k law faking resistors at the tapers to ground. The problem is that the resistor does not convert the linear to a perfect logarithmic, I mean the lower 20% and the upper 20% is unusable (lower end is too loud, volume does not change much in these regions). The usable range in the middle is about 25-30 dB at most, which is not enough. I tried with different law faking resistors, neither was better.

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