Balanced But Not Fully Balanced

I own a preamp which has both balanced and single ended jacks. I assumed that since I was using the balanced jacks I was getting the benefit of a balanced circuit. I have just now realized that just having balanced plug-ins doesn't mean your preamp (or any other component) is "balanced." Just wondering what sonic compromises are being made with equipment which has balanced inputs and outputs but changes the signal to single ended as it passes through it. If you are using the balanced outputs, what good is that if the signal going into this jack is single ended? I don't understand what good is it to offer equipment with balanced capability only to revert to single ended signals. Is this just a gimmick to sell equipment or is there some advantage to not making the circuitry "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.

-- 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.

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.
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

@almarg and @atmasphere

My sincere thanks to both of you. Very informative and rather prompt too I might add.

I have since asked Musical Fidelity. Their response:

"No it isn’t fully balanced. It is converted to single ended to work with the rest of the amplifier."

The aforementioned being the case, could you advise then whether or not it would be preferable to connect the amp to equipment that I believe purports to be fully balanced (specifically Emotiva ERC-3 and Oppo UDP-205) via XLR or RCA? I currently have it connected via XLR. Sounds great either XLR or RCA. Just wanting to know if theoretically better to connect via RCA when connecting a true fully balanced piece of equipment to a non-fully balanced piece.
Fully balanced equipment is always more expensive because the design has  separate circuits for the + and - portions.....  XLR connections on equipment makes for a selling point.  If you have both - try them both and see if you can hear a difference.
Hi Hal,

As you are aware, the Oppo player is clearly described as featuring "a true differential signal path all the way from the DAC to the 3-pin XLR connector." And as you indicated the Emotiva ERC-3 purports to be similar in that respect. However despite the ERC-3 being referred to as a "Differential Reference (TM) CD Player/Digital Transport," and despite suggestions in its manual that its balanced analog output is "generally preferred," IMO there is enough ambiguity in its descriptive literature to leave me at least a little bit uncertain as to whether its analog signal path is in fact fully balanced. Also, we have no way of knowing "a priori" whether the net result of the tradeoffs I referred to in my post above dated 9-20-2012 would work in favor of the balanced or unbalanced inputs of the M6si integrated amp.

So the only way to be confident of the answer to your question would be to try both players both ways. Which it sounds like you’ve already done, with similar results in each case. But if in fact there is any difference, given that the M6si has only a single XLR input, and given that the Oppo can be said with certainty to have a fully balanced analog signal path, my guess would be that the best odds of obtaining optimal results would be if you were to connect the Oppo via XLR and the Emotiva via RCA.

Best regards,
-- Al

@almarg and @stringreen 

Understood. Thanks!