Balanced Not really and Ground Hum

A truly balanced circuit has a pair of identical signal paths for each channel whereas an unbalanced circuit has only one signal path per channel. The duplicate signal path is for carrying an inverted version of the standard signal.

You can very quickly tell from glancing inside of an amp or preamp if it is a balanced or differential circuit. If it is, you will see four of every key part in the signal path (left channel +, left channel -, right channel + and right channel -). An unbalanced or single ended circuit will only have two of each component (left channel + and right channel +).

For a truly balanced system, every component from the source through the amplifier must have balanced circuitry. The noise reducing benefits of balanced operation occur when at the ouput of your amplifier, the inverted signal is inverted again and then summed with the standard signal. Any noise that was picked up via the signal paths in your equipment and any of your interconnect cables will be cancelled out, while the signal level will be doubled moving it 6db above the now lower noise floor.

Thanks problem solved well 90%
The culprit was the Bam for the Merlin VSM's Speakers.
I never disconnected this unit from the power it just did not occur to me that it would be the problem.
I have found that using it in Battery mode cuts down the Hum by 90%.

The original question is still what makes a balanced system, as Kjweisner pointed out that few companies make truly balanced systems in addition ALL components need to be balanced (Not an easy feat)
If the latter is true is running balanced from the Pre to the power amp and exercise in futility, also running a “not truly balanced" signal (see above) is this also a waste of time.

Case in point; I have a " Clearaudio Symphono " Phono Stage that offers RCA in and a choice of RCA or balanced out,
As my Turntable (Nottingham Dias) only has RCA from the tonearm would using the Balanced out be pointless.

And lastly apart from the lowering of outside noise what sonic advantages does a balanced IC offer over RCA IC's.
Without starting the how much is an IC worth thread, I see a multitude of balanced cables with the usual wide ranging of price, but is a $500.00 Balanced IC more desirable than a $2k RCA IC (The price is just hypothetical)

Are you saying that you totally disassembled your components and then added them back into the system, one at a time, and you didn't notice the reappearing hum at the time the offending was reinserted into the system? I agree with the above re ground loops v balanced.

If you start with sources, removing one at a time, you should notice when the cause disappears. If not, then when they are reassembled, one at a time starting at the amps it should appear. Just let some time lapse between each change - sometimes hums take a bit of time to reappear due to warm up issues, etc. (I have amps which hum immediately, and others that start to hum after substantial warm up. The former I have been able to 'fix' with cheater plugs, the latter not at all absent some overhaul, if that, but much depends on level and speaker sensitivity.

Once you ID the source, the solution is probably a walk in the park.

You are also correct that not all balanced outputs/inputs indicate truly balanced design. In fact, it's probably not "some" but "most" outputs that are not truly balanced. Companies such as BAT (Balanced Audio Technology) do build fully balanced designs whereby there are complete circuits for both the pos and neg "legs" of the run. Keep in mind that to leverage balanced, everything in the system, from source to amplification should be balanced. The primary benefit for full balanced is when there are long cable runs (which become antennae) a balanced line will cause interference introduced by this antenna effect to self cancel. I believe that balanced design may also enable the signal voltage to also be higher. You don't mention the lengths of your runs, but if you have a long one, then balanced may solve the issue.

If, on the other hand, your hum is a ground loop, this will make no difference. Spencer makes great points, especially concerning TT--I would add that if there's any cable TV, satellite or other video-oriented sources where RF cable is involved, they can be a source as well.

True balanced will help fight RFI and noise in general, and is a great idea, but really should be necessary to rid your system of a ground loop.
I suggest you read the archives on ground loops, both here and at audioasylum. Then I'd try borrowing other gear(e.g. cheap reciever) and trying to see if you can eliminate to isolate which component is causing the trouble. If you can narrow it down to your pre, call the manuf for suggestions. One obvious one is wires touching each other. Make sure your cables cross at right angles when possilbe and that no power cables touch each other or any interconnects.
Turntables are notorious for loop issues, so first try just CD, resolve the digital/amp/pre then add analog back and see if you still have no hum. Good luck,
Spencer

Hi,
Before you burn down the barn to get rid of the mice, get sombody with a technical background to come over and help. You are probably making the same mistake over and over, and a fresh mind may solve the problem easily. Recently I visited an MD with a hum problem that had defeated him. It was solved in five minutes by replacing his very expensive unshilded cables with cheap, but well shielded, interconnects.
regards,