3 preamps with transformer hum, DC on the line?

So, I took the case off the preamp today and tightened all power supply screws (none really budged). Powered it up with every breaker turned off except my dedicated 20 amp AV line and only the preamp plugged into the dedicated outlet. Still hums - grrrr.

It looks like I have very few options, some which I cannot afford and 1 I really am not sure I want to do:

1. Send back to Audio Plus Services (Seattle to NY). Anyone had any experience with this shop and their service dept? I can see a $250 diagnosis bill plus shipping both ways and them coming back saying there is either nothing wrong with it or they are unable to fix it. Really not sure about this route. Probably a No.

2. A custom or 3rd party power supply is probably out of the question after looking at various wires coming off the factory power supply. No.

3. Trying a PS Audio or similar power regenerator. Too expesive. No.

4. Going to an integrated amp if I can find an Audio Refinement Alpha Complete in black that does not hum in 8/10 shape I just might do it. I've heard it is a good unit but not as good as my Audio Refinement separates, especially the Pre 5. A Maybe.

5. Trying my best to get the power company come out and test the line. Hopefully something that is easily addressable and I can actually get the power company to show up and test the line and do it for free (I do pay them for a resource with hopefully some kind of service level agreement backing it.

6. Going to try a Environmental Potentials DigiPlug Stationary in series before my Porter Port on my dedicated 20 amp line. They will do a 30 day refund trial and I can do the wiring myself. A Yes and hope it fixes things.

What I really don't get is that all 3 preamps I've tried do hum and got better with using the PS Audio Humbuster, but again, I lost the high frequencies so the PS Audio Humbuster is out. If it is that common of a problem, why is there not more of an industrial standard that avoids this problem. On top of that, the Linn Classik K music (integrated amp with tuner and CD player) just cranks away with no hum but does not sound as good as my current Audio Refinement gear and probably loses out to the Audio Refinement Complete Alpha integrated also.

Things that annoy you with their hum...

BTW, the Linn Classik is part of my bedroom system with some Tukans and is not on a dedicated line and I have quite a few dimmers in the house.

Dimmer switches in the house? Removed mine and removed the hum.

Scott..Are you referring to an audible hum that you hear through the speakers, or is it a mechanical hum from the transformers themselves?

Jea48

From your reference:

"It's also worth noting that DC is usually not a problem with toroidal transformers of 300VA or less. Their primary resistance is usually high enough that any DC will have little effect."

"Most of the time, the DC offset is transient - it appears for a short while, then goes away again."

And it can be easily measured on a good Digital Volt Meter, like a Fluke or Tektronix. But you have disable autoranging.

Was surprised to see a slowly ocsillating offest of about +/-300 mV peak (at a frequency of 0.1 Hz) on my AC line, but none of my torroidal transformer powered equipment (2x Parasound JC1, a JC2, and a P3) hum at all, even with this amount of DC.