Hum in system when only amp is on


I am getting a hum when the amp is turned on but not the preamp. The hum goes away when the preamp comes on. Does any one have any ideas?
My system:
Theta dreadnaught 5 channels
Cary cinema 6 preamp
audioquest jaguar unbalanced rcas
dedicated outlets

Thanks,
Ian
ian_slater

Showing 3 responses by nsgarch

The arrows on the ICs connecting the preamp to the amp should point to the preamp. The preamp AC cord should be grounded, but the amp should not (it's grounded through the ICs and the preamp) and you should use a "cheater" plug on the amp's AC cord plug so that you are only plugging two prongs into the wall, not three.

Try those two things, and see if the hum doesn't go away.
Ncarv, you might want to read the description of their x-Stream power cords on the PS Audio site. They even provide their cords with a removable ground pin for that very purpose.

As for the arrow direction, Ian is using Audioquest single ended Jaguar ICs. These follow the standard Bruce Brisson "shotgun" design a la Monster, MIT, Straightwire, etc. Meaning that the shield is connected to the ground ring at the arrowhead end of the cable and not at the other end ("floated"). You want to drain the shield to the preamp, since in a star-grounding arrangement, that's the one grounded component. It really has nothing to do with signal flow since a cable will acclimate to either direction of signal flow during break-in. This unfortunate misunderstanding arose as a result of cable manufacturers wanting to give the consumer an oversimplified explanation for orienting their cables. And in fact it works when you're talking about source-to-preamp connections, but does not apply in preamp-to-amp connections -- UNLESS your amp is the only grounded component. However that won't give you star-grounding, which is the recognized best method for getting the most noise reduction.

Hope that explains it :~))
Ian, in my heart of hearts, I feel the warning from Theta is mainly a liability issue, and that you shouldn't be paranoid about ruining the amp if you float the ground . . . . . but if you are, then ground the amp, but not anything else (oh, and then point the arrows of the preamp-to-amp ICs toward the amp as I mentioned earlier.)

Neil

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