Living with unsolvable hum - Any audio detectives out there?


For over a year I have put up with a hum in my system, coming through the speakers (not chassis hum). I cannot make it go away. It seems to be related to the preamp because it stops when I replace the preamp. But I had my local tech hook up the preamp on his bench and it is quiet as a mouse. I've also corresponded with its designer, David Berning, who has been very responsive and helpful. But no luck solving it. I thought it may be related to the separate power supply's umbilical but David Berning said likely not. Earlier this year I even bought a star grounding component from Granite Audio and connected everything to it. Didn't work. After trying everything the engineer at Granite could think of (he was great), he was stumped too. These people have forgotten more than I'll ever know about the subject, so I gave up at that point and just lived with it. I had also tried everything they and a few knowledgeable friends have suggested (see below). But now I would like to take another swing at solving it. Any ideas? What kills me is that now I can't recall when it started, which would be very helpful to diagnose. The system sounds as good as I've ever had it now, and I LOVE the Berning preamp. So replacing it or other major components is not an attractive proposition for me.

For any intrepid detectives, here are the facts:

- Hum is typical 60 cycle sound- both channels equal volume of hum- loud enough to hear at the listening position, but just barely. Quite noticeable when standing at the rack.
- Hums with any source, not volume dependent, still hums with no source components attached (I even tried unplugged them from the wall too). But the hum stops if preamp is disconnected from amps.
- System plugs into a dedicated 20 amp line with eight plugs. Nothing else is on this circuit except my audio system. I had an electrician verify and tighten all the ground connections. The service is a relatively new 200 amp service. The electrician tested and found no ground issues or noise in the dedicated line.
- Tried shutting down all breakers in the house except my dedicated audio line. No effect, surprisingly. I had high hopes for that one!
- Tried cheater plug on everything including the preamp. No effect.
- Tried different interconnects between pre and power amps... No effect.
- Replaced all linestage tubes. No effect.
- Moved components around, moved the power supply, even used long interconnects to move the preamp three feet in front of the rack. No effect.
- Tried an extension cord to plug the preamp into a different AC circuit. No effect.
-The only thing I know of that could try, but have not tried, is replacing the power supply tubes, but I didn't bother because on the bench it made no noise for my tech.

My system:
- Power: Temporarily I'm using a Shunyata T6000 distributor (the hum existed prior to this, and the Shunyata didn't solve it). All Cardas Golden Ref or Golden power cords, except T6000 is plugged into the wall with Shunyata Sigma HC cord.
Analog: Koetsu Rosewood Signature Platinum, Jelco TK-850, Cardas Golden Cross phono cable
Digital: CEC transport and Audio Logic DAC, Golden Cross interconnect.
Preamp: Custom Berning Octal tube preamp with separate tube rectified switching power supply, built-in Jensen transformer MC stage at 24x gain (on the high side, I know, but it sounds amazing compared to other winding options)
-Power amps: Quicksilver v4 monos with KT150 tubes
-Two REL G2 subs (hum existed before them, and persists when they are disconnected and unplugged)
Somehow the interaction between the preamp and other components seems to be creating the problem. Source components don't seem to matter, but amps are Quicksilver v4 monos. Speakers are Verity Audio Parsifals. Interconnects, speaker cables and power cables are Cardas Golden Cross.
Speakers: Verity Audio Parsifal Encores. No surround sound or home theater.

montaldo
Lifting the signal ground is a fine idea, when there are multiple signal wires.

These are mono amps, so I would suggest the OP try cheater plugs on one or the other amp first, and if that works, get a hum buster (or whatever they are called).
Actually, the OP should unplug 1 mono amp from the power completely, and see if this doesn't fix it.
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This may sound crazy but have you lifted the ground on one channel at the power amp or, alternately, the pre-amp?  Kerry_
Might be gain sensitivity on the amp- must be too high and therefore picking up an otherwise inaudible hum. Ask Bering about padding it down perhaps.
Ok before you go out and buy anything, do this first!

Take a good look behind your equipment. Look at all the power and signal cables. Make sure all of them cross each other at about 90 degrees. No parallel cables should be touching or near each other.

Anything running parallel should be at least 12" apart...better if it is 18".

To some degree, reorganize your components to accommodate better cable management.

Undo looping cable. Use shorter and longer power cables to tailor to the need.

If you need, use small blocks of wood or zip ties or velcro to create separation and organization.

Also get rid of wall warts and non audio equipment connected to the line.

Separate the analog stuff from the digital stuff. They should not share the same line.

This worked for me...and I have 2 dedicated audio lines. The noise appeared when I quickly and carelessly changed out my power conditioner for another. The noise is most likely coming from your own equipment.

Look inside any point to point wired preamp or amp...everything crosses at 90 for this same reason.