law faking pot Q

pjanda1 · 27th March 2005, 01:56 PM

Happy Easter! I'm going to try a PEC 1M linear pot T recommended in my BrianGT 3875 project. I recall T writing that the appropriate law faking resistor value is 33K-47K. Is there an advantage to either end of the spectrum? I believe that 47K should result in a better taper. But if I use 33K will I be able to remove the 22K resistor at the input as P.D. does with a 25K pot? Sorry if these questions have been answered before, but I can't find them. I know the best way is to try different configurations, but I want to get as close as I can to begin with.

thanks,

Paul

mwmkravchenko · 27th March 2005, 02:11 PM

THe best way is to try it and plot the values on graph paper. To get some measure of repeatablity you might want to mark out points on the dial and plot them on some graph paper. You will be happy with either. But the higher resistance will give you what you want.

Mark

richie00boy · 27th March 2005, 02:21 PM

To save you all that do a search on 'law faking' for posts in the last 6 months and you will find a spreadsheet.

homer09 · 27th March 2005, 06:52 PM

You will find my spreadsheet here:

*technical elec question* DC offset/input impedance relation

pjanda1 · 28th March 2005, 07:33 AM

Thanks homer09! That was exactly what I needed. For some reason I was having a hard time finding that post in my searches. I needed to search for "linear" instead of "law faking". Did you end up going that route, and if so, what did you use?

richie00boy · 28th March 2005, 08:07 AM

That's the spreadsheet I was on about. homer09 wrote it so I'm sure it was easy for him to find

Sorry I wasn't too good with my search instructions, I couldn't quite remember the exact thread it was in.

homer09 · 28th March 2005, 05:06 PM

Quote:

Originally posted by pjanda1
Thanks homer09! That was exactly what I needed. For some reason I was having a hard time finding that post in my searches. I needed to search for "linear" instead of "law faking". Did you end up going that route, and if so, what did you use?

Glad to help

I havent actually tried law faking for real yet, my amp building project is a very slow and ongoing task...

i am in university full-time, so this can't be a priority. But, I am planning to implement a fake-law in the amp i will be starting/finishing within a month and a bit. I chose a 250K linear PEC pot, and im leaving the 22K shunt resistor in place on the BrianGT LM3875 board. I think this should give a nice volume curve.

If you jump ahead with your 1Meg pot, i would love to hear your results! post them on the thread with the spreadsheet.

27th March 2005, 01:56 PM	#1
pjanda1 diyAudio Member Join Date: Jan 2005 Location: Boulder, CO	law faking pot Q Happy Easter! I'm going to try a PEC 1M linear pot T recommended in my BrianGT 3875 project. I recall T writing that the appropriate law faking resistor value is 33K-47K. Is there an advantage to either end of the spectrum? I believe that 47K should result in a better taper. But if I use 33K will I be able to remove the 22K resistor at the input as P.D. does with a 25K pot? Sorry if these questions have been answered before, but I can't find them. I know the best way is to try different configurations, but I want to get as close as I can to begin with. thanks, Paul

27th March 2005, 02:11 PM	#2
mwmkravchenko Mark Kravchenko --- www.kravchenko-audio.com diyAudio Member Join Date: Jan 2002 Location: Perth Canada	Try it! THe best way is to try it and plot the values on graph paper. To get some measure of repeatablity you might want to mark out points on the dial and plot them on some graph paper. You will be happy with either. But the higher resistance will give you what you want. Mark __________________ Mark

27th March 2005, 02:21 PM	#3
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	To save you all that do a search on 'law faking' for posts in the last 6 months and you will find a spreadsheet. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

27th March 2005, 06:52 PM	#4
homer09 diyAudio Member Join Date: Jan 2004 Location: Montreal	You will find my spreadsheet here: technical elec question DC offset/input impedance relation __________________ Most people wouldn't know good music if it came up and bit them in the ***. - Frank Zappa

28th March 2005, 08:07 AM	#6
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	That's the spreadsheet I was on about. homer09 wrote it so I'm sure it was easy for him to find Sorry I wasn't too good with my search instructions, I couldn't quite remember the exact thread it was in. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more


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28th March 2005, 07:33 AM	#5
pjanda1 diyAudio Member Join Date: Jan 2005 Location: Boulder, CO	Thanks homer09! That was exactly what I needed. For some reason I was having a hard time finding that post in my searches. I needed to search for "linear" instead of "law faking". Did you end up going that route, and if so, what did you use?

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