signal, safety grounds and hum???

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Hi folks,
I could use a little help if you may be so inclined. With all my DIY projects over the last 30 yrs. (preamps and poweramps) I have always attached safety ground to a single point chassis ground. This single point was also the bus to which all signal grounds were brought i.e. a star ground. It was located very close to the ground lug of the first filter cap off the rectifier. This included input jacks, transformer secondaries, and local stars from various power supply cap farms, driver stages, etc. I have never had hum no matter what source I used. I've also mixed in many commercial preamps, power amps and analog and digital sources (some with safety ground, some not) over the years and again, never any hum.
I recently acquired a Cary V12R power amp and it hums if I don't lift the safety ground. It hums with no signal and hums slightly worse (with a buzz) when the preamp is connected (RCA). I havenâ€™t tried a balanced preamp as I don't have XLR terminated cables long enough.
While the hum is audible from the listening position, it does not increase with volume so essentially it is "swamped" out. Still, I'd like to be rid of it.
I know that one school of thought says to only connect the safety ground on one component, but I've never had to do that â€¦ right or wrong. OR is it don't connect the signal ground to the chassis on all but one component.
AC power is supplied to all amplifiers via equal length 3-conductor power cords (Belden 83802) that are hard wired to one common junction box. Digital front end components have a similar arrangement from their own box. Each box is a dedicated circuit.
Any insight most appreciated,
Thom

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Topic - signal, safety grounds and hum??? - Thom 07:34:39 08/30/06 (6)

I don't know if this will help... - RioTubes 07:40:26 08/31/06 (0)

Re: signal, safety grounds and hum??? - erik_squires@hotmail.com 18:47:32 08/30/06 (0)

Are the chassis touching each other like in a metal rack?nt? - grhughes 09:47:14 08/30/06 (1)

good point, but no, not even close ... - Thom 11:33:58 08/30/06 (0)

Re: signal, safety grounds and hum??? - twystd 08:48:24 08/30/06 (1)

interesting ... - Thom 11:36:48 08/30/06 (0)

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