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Old 3rd May 2006, 05:52 PM   #1
mudihan is offline mudihan  United States
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Default Pot for a passive preamp

I am using Art Dio, which has about 7-9v of output, as the source. Is 10K still the best value for a simple passive preamp (RCA-in+pot+RCA-out)? Or should the impedance be higher or lower? Some passive preamp schematics have a 1k resistor before the pot, why? Thanks!
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Old 4th May 2006, 06:56 PM   #2
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Hi, It depends on the impedance of the amplifiers input and your preamps output impedance, if the i/p z is about 40k you'll be o.k, if it's significantly lower, you 'll have to keep the interconnects short ( shorter the better anyway)
as the capacitance of the cable will filter off some of the hf.
As for the resistor in the schematics, my guess is it's a law faking resistor to make a linear pot behave like a log pot, Audio Synthesis used to do this.
No doubt someone else can give you a better technical explanation.
Jules
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Old 5th May 2006, 04:45 AM   #3
mudihan is offline mudihan  United States
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Thank you. The input impedance is 22k. My cables are very short (10 inches) and have very low capacitance. In my case, with the output being strong, would you still recommand a 10k pot or a pot of other values? Thanks!
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Old 5th May 2006, 04:49 AM   #4
jleaman is offline jleaman  Belgium
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You could try one of these


http://welbornelabs.com/remote.htm

I think i might.
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Old 5th May 2006, 10:11 PM   #5
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With such short cables, I can't see a problem,
do you know the output Z of your source? if it's nice and low
You could go to a 5k pot ( stepped attenuators sound better, but that's perhaps for another day).
Jules
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Old 5th May 2006, 11:21 PM   #6
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DACT is a nice attenuator and I'm using one in by BOSOZ right now.

They have a design for a pasive preamp using their attenuator.
wiring Diagram
http://www.dact.com/html/wiring_a_ba...reo_passi.html

DACT Passive preamp article
http://www.dact.com/html/passive_preamp.html

Complete DACT passive preamp design by one of their customers
http://kotiweb.kotiportti.fi/audiovideo/DIY/preamp1/

-David
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Old 5th May 2006, 11:39 PM   #7
jleaman is offline jleaman  Belgium
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Quote:
Originally posted by dw8083
DACT is a nice attenuator and I'm using one in by BOSOZ right now.

They have a design for a pasive preamp using their attenuator.
wiring Diagram
http://www.dact.com/html/wiring_a_ba...reo_passi.html

DACT Passive preamp article
http://www.dact.com/html/passive_preamp.html

Complete DACT passive preamp design by one of their customers
http://kotiweb.kotiportti.fi/audiovideo/DIY/preamp1/

-David

Id have to say that dact's make to much noise and they wear out to fast.
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Old 6th May 2006, 12:48 AM   #8
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I have the DACT2 and it is very quite. The Emla switch is of very high quality. The thing is dead silent while turning it to adjust volume.

There's a clear plastic shell around each deck of the switch and the machining and finish of the gold plated contact points look great.

Don't know what to say other than Elma's are great switches.

-David
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