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stevief198 10th August 2010 10:48 PM

passive noble 10k preamp loud buzz

please help, I am trying to build a passive preamp using a 10k noble pot but I am getting terrible buzz as soon as I connect my loudspeakers to the power amp.

My wiring must be shoddy but to me it looks ok. I am unsure as to how to wire my female rca's (inputs) particularly the negative side as there is no connection to the pot and also wiring the ground outputs from the pot.

please help otherwise I have wasted a lot of time and money.


DougL 11th August 2010 04:19 AM

Steve, a wiring diagram / schematic and a photo or two might get something started.
Without that I personally decline to guess.

By the way, whats the output impedance of your source, and what is the input impedance of your amp?


stevief198 11th August 2010 02:15 PM

Thanks Doug,

I think i have worked out my problem. I haven't wired the left and right input grounds into the noble pot. I will connect these tonight and retest. At the moment I have one set of inputs going through the pot to a pair of outputs acting as a simplistic preamp to a quad 303. My source is a slightly modded marantz cd63 ki Sig. I will post my results.
Cheers Steve

DougL 11th August 2010 03:53 PM


The Quad 303 has an input Z of 22K ohms in parallel with 60pF.
This may or may not be a good fit for a 10K pot. I might consider building a B1 buffer.


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