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In Reply to: Re: Then you have built yourself some sort of earth (hum) loop into... posted by breadhead on April 6, 2007 at 03:42:29:
To be pretty direct - so what?Something somewhere is sharing powersupply AC current with signal circuits, and the most likely cause is the earth wiring.
For instance ,if you have several amps of 60Hz AC for the heaters sharing the same piece of 12ga. as the input circuit you'll have hum big time - because even if the DC resistance of the 12ga. is only milliohms you could still be generating many millivolts of 60Hz (and higher harmonics) which end upsuperimposed on the input.
And as it changes when the amp warms up and can be (partly) nulled out with a particular setting of the volume control, it means to me 100% the presence of an unexpected earth loop.
Keep hunting!
Regards, Allen
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Follow Ups
- " I am currently using a 12ga. bus for ground" - Allen Wright 07:54:03 04/06/07 (5)
- Implementation mistake - breadhead 11:04:39 04/06/07 (3)
- "I noticed that the signal input is not referenced to ground in any way" - Allen Wright 12:41:45 04/07/07 (2)
- Guess what I meant was... - breadhead 16:40:10 04/08/07 (0)
- Been doing some online studying - breadhead 16:36:45 04/07/07 (0)
- Re: " I am currently using a 12ga. bus for ground" - breadhead 09:19:03 04/06/07 (0)
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