Need help solving hum problem

This one really has me stumped....

The system:
Sony SCD-777ES
analog out into Placette Active Line Stage
digital out into Dodson DAC into Placette
Turntable also into Placette
Placette into CJ11A
ALL front end components plugged into Shunyata Hydra PLC

I get constant, low-volume hum when the Placette is switched to either the Dodson OR the Sony analog out, but not when switched to vinyl or any unused input.

The problem is cured when the Dodson is plugged into another outlet (same circuit). Why would the Dodson contaminate the system at all, and (this is the kicker) for two of the sources (itself and the Sony analog out) but not for the phono?

Any ideas? thanks. --dan
I don't know what to tell you but i can relate. Have had similar problems with a DAC and specific preamp. Out of curiosity, is the Dodson an upsampler ? Sean
Yes, it is.
Well from experience in hooking up litterally hundreds of sytems over years, I can get rid of pretty much any hum from tinkering a bit I suppose. Usually you should first try using a cheeter plug on one of your 3 prong plugs, either on the preamp or amp first.(they'll all still be grounded through connection to one another). Usually, this solves the problem of blatent hum off the bat. Sometimes interconnects or speaker wires are running next to power cords too closely for stretch, and can have hum in the wires that way, but usually not. I have run speaker wires next to high voltage cables with loud buzzing and humming, that's to be considered.
I once hooked up a really really long pair of Interconnects down 2 sides of the room, running along the same path in a wall with some power cords, and it buzzed like crazy.
Anway, hope that gives some food for thought. But I think you might try the ground cheater plug thing first. That usually works. Then, you can try moving your interconnects around, while your system is playing, and see if it's a problem. You might find that if you get the interconnects to lay in a certain way, you'll virtually eliminate hum sometimes.
Good luck
Thank you. I had tried a cheater on both the DAC and the preamp, with no success. I will try it on the amp, but as I said, the hum goes away if the amp and DAC share the same wall outlet. Based on the results of my various troubleshooting attempts, I don't think that the location or proximity of components and cables is the issue in this case, but I do appreciate that those can be factors in system noise.
I have tried EVERYTHING known to man to minimize the hum that i'm experiencing. I'm wondering if it doesn't have to do with how these designers are are using the upsampling devices and trying to keep circuitry to a minimum ???

I recently did a "tweak" that did help this out a bit while making other noticeable improvements though. Since this applies to and can benefit ALL systems, i don't want to "pigeon hole" it to this thread. Look for a new thread on the subject in the next 24 hours. Sean
(a bit chagrined...) I thought that I had tried lifting the ground on the Dodson. But I happened to try it again, and it seems to have fixed the problem.

Nevertheless, I will attempt to work through the process Sean describes in his excellent other post.
Appears I spoke too soon. It's baaaack.....
I have found the easiest way to eliminate the hum is to isolate where it is comming from and then teach it the words. This works for any whistles you might come across.

I think it's time for me to go to bed.
Is the hum coming from the speakers or the amp's transformer?

General things to try:
1. Float or lift or disconnect the ground on all electrical lines to all audio components. This includes a tv if shared with the audio components or even the vcr if the vcr audio outs go to the preamp. I'm sure you don't but you never know.

2. All of your components should share the same ground or no ground at all. You could have half of your components grounded and half not grounded. But just make sure the ones that are grounded are sharing the same ground.

3. If you narrowed the hum down to the amplifier's transformer, try to determine which circuit the amplifier is running off of. Then check the circuit breakers in the service panel.

Chances are that your amps' circuit is on the opposing phase of some or all of your other audio circuits and therefore generating some AC noise thats affecting the transformer.

Have an electrician move all of your audio circuit breakers in the service panel to the same phase of 115 volts.

Just for grins I moved my amp's circuit over to the opposing phase where my other dedicated audio circuits are to see what sonic improvements I may find. No sonic improvements that I could tell but it instantly cured my amp's transformer hum and the transformer has been almost dead silent every since.