Law faking issue

oshifis · 4th April 2008, 01:08 PM

I am trying to use a 100k lin pot with law faking resistor for volume control. Initially I put a 47k resistor between the taper and GND, but then the volume was too high throughout most of the range, and the change at the bottom end was very abrupt. Then I replaced the resistor to 6.8k. Now the volume is acceptable, but the volume difference between say 1/5 and 4/5 (30 degree to 270 degree over a 300-degree range) turn is quite small, about 20 dB. Normally I never use it over 4/5 (which is 20 dB below maximum BTW), but I want to use it below 40 dB attenuation, which is below 1/5. My problem is that resolution and channel tracking is not very good there. It seems to me that law faking with good resolution is usable over a 20 dB range only. Is there any trick to improve it?

AndrewT · 4th April 2008, 01:22 PM

yes,
setting the faking resistor to between 10% and 15% of the pot value.
Try some values between 10k and 15k.

The LIN pot is recommended only because of better tracking at low volumes.

But your Zin >=5times Rfake and preferably >=100k.

You may find that Zin is already working as a law faking resistor if it is below 20k.

337alant · 6th April 2008, 08:57 PM

Andrew
If I have a power amp with an input sensitivity of 20mv, what would be the best pot to use?,
I have been using a 10k pot but the volume is too high at only level 3, so I guess I should up that to say 200k linear and a 20k law faking resistor? is that about right

4th April 2008, 01:08 PM	#1
oshifis diyAudio Member Join Date: Mar 2004 Location: Budapest, Hungary	Law faking issue I am trying to use a 100k lin pot with law faking resistor for volume control. Initially I put a 47k resistor between the taper and GND, but then the volume was too high throughout most of the range, and the change at the bottom end was very abrupt. Then I replaced the resistor to 6.8k. Now the volume is acceptable, but the volume difference between say 1/5 and 4/5 (30 degree to 270 degree over a 300-degree range) turn is quite small, about 20 dB. Normally I never use it over 4/5 (which is 20 dB below maximum BTW), but I want to use it below 40 dB attenuation, which is below 1/5. My problem is that resolution and channel tracking is not very good there. It seems to me that law faking with good resolution is usable over a 20 dB range only. Is there any trick to improve it?

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4th April 2008, 01:22 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	yes, setting the faking resistor to between 10% and 15% of the pot value. Try some values between 10k and 15k. The LIN pot is recommended only because of better tracking at low volumes. But your Zin >=5times Rfake and preferably >=100k. You may find that Zin is already working as a law faking resistor if it is below 20k.

6th April 2008, 08:57 PM	#3
337alant diyAudio Member Join Date: Feb 2008	Andrew If I have a power amp with an input sensitivity of 20mv, what would be the best pot to use?, I have been using a 10k pot but the volume is too high at only level 3, so I guess I should up that to say 200k linear and a 20k law faking resistor? is that about right