I asked this question, balanced OR unbalanced, of a well known equipment evaluator and review writer for Widescreen Review about this and here are his responses, paraphrased into one quote.

Is it ready for shipping?

LQQK

The Model 990? The first batch of production units is apparently crossing the Pacific on a freighter at this very moment.

it would be nice to be able to run a balanced line for those of us who have balanced inputs on our subs... i am assuming the 990 has a balanced sub pre-out...

there are no ill effects from having a balanced cable carrying your lfe signal.

Well, I count eight balanced connections on the rear panel . That leads me to assume that one of those is a subwoofer connection.

The even order distortion cancellation that Soundhound mentions is a characteristic of the balanced stage itself. In other words, it cancels the even order distortion products that the stage would otherwise produce itself were it not a balanced design. All circuits produce some distortion products and it is the ratio of even to odd harmonics that he is concerned with. With many off the even order (euphonic) harmonics cancelled, the more harsh and offensive odd order harmonics are unmasked and become the dominant sonic characteristic of the amplifier. This is a separate issue from the noise rejection abilities of the balanced input circuit.

Apologies to Soundhound if I have mischaracterized his opinion, which he is more than capable of defending himself.

Balanced does not remove noise. Noise is random and in fact as soundhound mentioned, noise will actually go up (3 db I think) in a balanced configuration. This is because you have 2 input stages producing uncorrelated noise from the stage. What balanced does do is remove common mode signals from the signal pair. A differential input has a figure of merit referred to as CMRR, or commom mode rejection ratio. If the differential signal coming in had a 60Hz signal injected onto both +/- inputs from wire coupling, then the signal would be reduced by the CMRR. CMRR's are usually frequency dependant with low frequencies getting rejected better. This is good for audio as mostly your trying to get rid of hum. Since hum is often injected by power cables running near audio cables, the balanced can save some cable placement issues. I suspect there are cases where ground loop problems will be minimized by balanced too.

Hope this helps
Mike

This still makes no sense to me. A balanced circuit cancels out *all* of the *common* components that are out of phase with respect to the other line. There is no difference between even or odd order.

This might not be 100% correct, but here's how I think about it: If I start with a simple 20 Hz tone, 2nd order harmonic is 40 Hz, 3rd order is 60 Hz, 4th order is 80 Hz, n * 20 Hz, etc. I don't think it matters what the order is.

I have read *a lot* about balanced circuits in my lifetime (and forgotten a fair bit too ), and I've never seen any discrimination mentioned before between even and odd order harmonics.

??

You are completely confusing the action of a balanced connection with a balanced design. As has been stated in this thread by Tekdredger and Stabie, a balanced connection only cancels what noise is picked up by the cable connecting two balanced components (these can be unbalanced designs but have a balanced receiver and transmitter on each end). The distortion of the other component(s) is unaffected except for the distortion actually generated by the transmitting and receiving electronics.

A design that is completely balanced internally will cancel all even order harmonic distoriton that is generated within that component only, and pass through the odd order ones. If you have a power amplifier that is balanced all the way through, the only distortion components that that amplifier produces that will be present on it's output will be the odd order ones.

Any distortion that is generated by other components upstream will pass through that power amplifier unaffected because obviously the balanced amplifier doesn't know what is music and what is distortion in material that is presented to it's input.

The balanced amplifier however will add only odd order harmonic distortion to the signal.

One of the major reasons that vacuum tube amplifiers sound so musical is the fact that the majority of what distortion they produce is even order. What odd order distortion that they produce is essentially non-existant beyond the 3rd order.

Designing a component that is balanced all the way through from input to output is a bad design decision. There is absolutely no advantage sonically or theoritically to this type of design. There is however the very real and very audible downside of this type of design which is a result of the cancellation of all of the even order harmonic distortion components that that amplifier produces.

If an amplifier must have balanced inputs, the least soncally degrading way to accomplish this is to design a standard unbalanced circuit and add balanced-to-unbalanced circuitry at the amplifiers input which can be bypassed if the user is only using an unbalanced connection.

Do you have any references for this? A lot of higher priced amplifiers *do* have fully balanced designs (one of the more cost effective ones being ATI, actually), and I have never heard this mentioned before.


Plus, the 990 will not be a fully balanced design anyway. It will have balanced outputs, but I doubt it will even have dual differential DACs.