Passive pre

raymondo · 5th December 2008, 10:11 AM

Hi all

I have a very high quality Penny & Giles pot I acquired from a previous employer when it shut down, it was custom built for the speaker ouput control in a £400K mixer. I think the pot itself cost us £200 at the time from P&G, hand made laser trimmed etc as I recall. It has very accurate channel balance , thats why it was so expensive, 0.1db from what I remember.
Anwyay I fancy knocking up a passive pre using it. Its 10K log (hope its log anyway trying to find the cct it was used in..).
I would be connecting it between cd player and the input of my power amp which has a 33k imp.

Would this be ok? Or will I get hf trouble? I seem to remember last time I looked into passive pre it was advisable to use high impedance pot.

Advice welcome.

thanks folks ;-)

analog_sa · 5th December 2008, 10:29 AM

Sounds fine. You should be able to confirm the log characteristic with your multimeter. Higher impedance pot is not preferable unless you have a very anaemic tube source.

raymondo · 5th December 2008, 10:44 AM

great . thanks.
yes i will measure the pot. im at work now so its not here. i found it under the stairs other day and thought hmmm i should do something with that ! :-)

sreten · 5th December 2008, 03:36 PM

Hi,

You get h.f. trouble with high impedance pots and long cables
from the pot to the power amplifier. 10K log should be fine for
1m to 2m of average capacitance cable, though of course you
can make it shorter.

/sreten.

5th December 2008, 10:11 AM	#1
raymondo diyAudio Member Join Date: Feb 2004 Location: manchester	Passive pre Hi all I have a very high quality Penny & Giles pot I acquired from a previous employer when it shut down, it was custom built for the speaker ouput control in a £400K mixer. I think the pot itself cost us £200 at the time from P&G, hand made laser trimmed etc as I recall. It has very accurate channel balance , thats why it was so expensive, 0.1db from what I remember. Anwyay I fancy knocking up a passive pre using it. Its 10K log (hope its log anyway trying to find the cct it was used in..). I would be connecting it between cd player and the input of my power amp which has a 33k imp. Would this be ok? Or will I get hf trouble? I seem to remember last time I looked into passive pre it was advisable to use high impedance pot. Advice welcome. thanks folks ;-)

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5th December 2008, 10:29 AM	#2
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	Sounds fine. You should be able to confirm the log characteristic with your multimeter. Higher impedance pot is not preferable unless you have a very anaemic tube source.

5th December 2008, 10:44 AM	#3
raymondo diyAudio Member Join Date: Feb 2004 Location: manchester	great . thanks. yes i will measure the pot. im at work now so its not here. i found it under the stairs other day and thought hmmm i should do something with that ! :-)

5th December 2008, 03:36 PM	#4
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, You get h.f. trouble with high impedance pots and long cables from the pot to the power amplifier. 10K log should be fine for 1m to 2m of average capacitance cable, though of course you can make it shorter. /sreten.

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