Balanced But Not Fully Balanced

Regardless of whether or not the component has a balanced internal signal path (i.e., is "fully balanced"), a well designed balanced interface will reduce susceptibility to ground loop effects; will to some degree reject noise/RFI/EMI that may be picked up in the cable; and may also reduce sensitivity to cable effects and cable differences.

Having a fully balanced internal signal path provides additional benefits that are essentially unrelated, including reduction of certain forms of distortion.

However, the potential advantages of using a balanced interface between components having unbalanced internal signal paths will in some cases be outweighed by adverse sonic effects of the circuitry required to convert the unbalanced internal signals to the balanced signals that are provided to output connectors, and to convert the balanced signals at input connectors to unbalanced form. Also, I suppose that at least a few highly compromised designs may exist that don't bother to include any conversion circuitry, and instead provide unbalanced signals to XLR connectors, which would negate the potential advantages of a balanced interface.

So if the components provide both choices, and are not fully balanced, the only way to determine which interface will perform best in your particular setup is probably to try both of them.

Regards,
-- Al

If the gear uses transformers for input or output, then it can operate fine in the balanced domain with no tradeoffs. But preamps with input or output transformers are rather unusual.

Balanced operation was originally conceived to eliminate problems with interconnect cables and it does that very well, in fact so well that it does not matter if the equipment is balanced or not if it can drive the cable correctly- the difference is that profound. Its how the record industry was able to hang mics in a concert hall 50 years ago and at the other end of 200 feet it still sounds like music :)

But a lot of companies just install the XLR cable to be trendy. If that is what you have it will probably work no better than the RCA connection.

@almarg and @atmasphere 

I realize I am resurrecting an old thread, but only because the two of you have chimed in on this one do I prefer to do so instead of creating a new one :) Hopefully you will appreciate the question.

How can one determine if their amp is "fully balanced"? 

In my case I have a Musical Fidelity M6si. I do not find this information on the manufacturer or other websites.

Thanks.

There is no good way to know without really understanding circuitry when you see it, so usually the best means is to ask pointed questions of the manufacturer. Quite often though the fact that the circuit is 'fully balanced' will be a selling point, so it should not be hard to sort out.

@gdhal
Hi Hal,

In the case of an integrated amp (or a power amp), if the design is fully balanced there usually will be statements in the manual and/or marked on the rear panel cautioning against connecting the negative speaker-level output terminals to any kind of ground point.   Since in the case of a fully balanced amp that terminal provides a full amplitude signal, having opposite polarity relative to the signal on the positive output terminal, which of course should not be provided with a path that would result in its being shorted to the amp's circuit ground.  And I see no such indication in the manual or in rear panel photos of the M6si.

That same caution, btw, would apply in the case of an amp whose outputs are internally bridged, as well as in the case of some older class D amps whose + and - outputs are offset from ground by a substantial DC voltage.  So while the absence of such a statement is usually a pretty good indication that the amp is not fully balanced, the presence of such a statement does not necessarily indicate that the amp is fully balanced.

Also, as Ralph indicated above I would expect that the manufacturer's description of a fully balanced amp would usually proclaim that fact proudly and prominently.

Best regards,
-- Al