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3rd May 2006, 05:52 PM
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#1 |
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diyAudio Member
Join Date: Jan 2004
Location: Texas
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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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4th May 2006, 06:56 PM
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#2 |
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diyAudio Member
Join Date: Apr 2002
Location: Wales u.k.
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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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5th May 2006, 04:45 AM
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#3 |
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diyAudio Member
Join Date: Jan 2004
Location: Texas
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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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5th May 2006, 04:49 AM
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#4 |
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Banned
Join Date: Apr 2002
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5th May 2006, 10:11 PM
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#5 |
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diyAudio Member
Join Date: Apr 2002
Location: Wales u.k.
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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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5th May 2006, 11:21 PM
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#6 |
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diyAudio Member
Join Date: Oct 2003
Location: San Jose
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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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5th May 2006, 11:39 PM
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#7 | |
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Banned
Join Date: Apr 2002
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Quote:
Id have to say that dact's make to much noise and they wear out to fast. |
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6th May 2006, 12:48 AM
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#8 |
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diyAudio Member
Join Date: Oct 2003
Location: San Jose
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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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