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It is currently 27 Oct 2020, 21:38

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PostPosted: 31 Aug 2020, 20:52 
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Joined: 15 Feb 2020, 18:53
Posts: 14
I am using either a Thorens TD-165 via The Boozhound deluxe phono preamp or my iphone via a 4S preamp. With no source connected and the volume above 75% I get a slight same audible (with my ear a foot from the speaker) hum. With either of the sources connected its a little louder (or more like deeper).
I'm not too worries about it, as I don't crank the volume that high but for my education, how would I go about checking the grounds for a source?


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PostPosted: 01 Sep 2020, 21:15 
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Joined: 04 Jun 2008, 20:59
Posts: 4258
Location: Arizona, USA
Hi, I wonder if it is making a ground loop through the AC mains. The design of the minis uses a three wire power input with the earth ground going to the chassis. This is in accordance with nearly all electrical codes. Be sure that you don't have any other grounds between the preamps and the amps (like an external wire). Also the drive tube is slightly sensitive to hum and emi pick up so the amps should not be really close to anything that might radiate significantly. Other thoughts...is the turntable(s) grounded to the preamp? Are they three wire powered and possibly not having the chassis isolated from the signal ground? Some still use the chassis for signal grounding and it can cause a ground loop through the AC.

What is the output impedance of the preamp(s). If it is really high that might cause issues. The amps are designed on a typical signal impedance of up to about 50K with 10K being optimum.

Did you have to physically relocate any of the components (turntable preamp etc) to set up the present system. Sometimes that can cause one to put out or be sensitive to hum.

Let us know what you discover as the amps if built like the ones in the project are really quiet.

Good listening
Bruce

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PostPosted: 03 Sep 2020, 13:26 
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Joined: 15 Feb 2020, 18:53
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Thanks, I probably won't have time until the weekend but I will do some fidgeting around and see if I come up with something.


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