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Passive Preamp Hum
Passive Preamp Hum
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Old 17th October 2002, 09:06 AM   #11
yeti is offline yeti  Germany
diyAudio Member
Join Date: Nov 2001
Location: Ewersbach
Default pot

What I meant was from input hot to ground, this will pull down the interferences.
Usually the output of your source device is in the range of a few ohms to aprox. 100 - 470 ohms, so the voltage loss will not be too much.

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Old 16th November 2002, 03:51 AM   #12
transducer is offline transducer  Canada
diyAudio Member
Join Date: Mar 2002
Location: Toronto, Canada
Default Success!


Well, it only took me a month to get around to soldering in a couple of resistors, but I finally put an 18k (it's what I had) resistor across each input to ground tonight, and it worked The passive preamp is absolutely silent! Even at maximum volume, with my ear against the speaker, I don't hear anything. Thanks very much for the helpful tip.

Now my only problem is that this pre was built for my cousin, who is coming tomorrow to collect it. But it sounds more transparent than my DIY active pre based on the BB OPA627BP opamp And I'm using cheap metal film resistors and a Radio Shack volume control.

For anyone wanting to build a passive preamp, I highly recommend HH's design with Arne's mod of the input resistor across ground. Resistor values are not critical, I used a 100k pot, an 18k resistor across input, and somewhere around 20k for the series resistor.

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Old 12th June 2015, 10:20 PM   #13
imkhawx is offline imkhawx  Singapore
diyAudio Member
Join Date: Aug 2012
Default hum problem on my passive pre.

Hi guys...

I am new to diy and i just built a passive pre and i am having the same trouble as transducer. I have read the posting and I don't understand what transducer and yeti means.

do i have to add in a resistor from the rica grounding tabs to the chassis ground?
I had a common copper wire from all the RCA grounding tabs of the inputs to the chassis.

so should I add a resistor across from each input grounding tab to ground or will one common resistor do?

thanks in advance.

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