XLR to RCA Adapter Dilemma

There is no way to provide a definitive answer without knowing how the output circuits of the preamp are designed. But it is certainly plausible that the sound could be significantly different for the two connection arrangements, for reasons that have nothing to do with the adapter itself.

I would expect that in many and probably the majority of designs there would not be a significant difference between the two configurations in the voltage seen by the power amp, because when using the preamp's balanced output in conjunction with an XLR-to-RCA adapter you are only utilizing one of the two signals in the balanced signal pair. In many (although certainly not all) situations where a volume increase such as 6 db occurs balanced vs. unbalanced the voltage of each of the two signals in the balanced signal pair is the same as the voltage of the unbalanced output. But since the two signals in the balanced signal pair are inverted relative to each other (i.e., 180 degrees out of phase) the DIFFERENCE between them at any instant of time, which is what a balanced receiver circuit would respond to, would be twice as much as the voltage of the single unbalanced output signal of the same component.

Do you tend to set the volume control at about the same positions in the two configurations? If so, differences in voltage are probably not the explanation.

Another possibility is simply that the output stage which drives the two signals that are supplied to the XLR connector may be independent of the output stage which drives the signal that is supplied to the RCA connector, and may have significantly different design characteristics, including output impedance among many other possible differences. As I say, the question can't be definitively answered without being familiar with the internal design of the preamp.

In saying all of this, btw, I'm assuming that you are using the same RCA-to-RCA cable in both cases, and when you utilize the XLR output of the preamp you are using an XLR-to-RCA adapter at the preamp's output. As opposed to running an XLR cable from the preamp output and using an adapter at the power amp input, which would introduce additional variables into the mix.

Regards,
-- Al

Peter (Pbnaudio), thanks very much for your comment, which I reciprocate :-)

11-30-13: Rlb61
Also, to Elizabeth ... thanks for validating that practical application can trump theory. For a minute there, I was beginning to doubt myself because the theorists maintained that what I was hearing was simply impossible.

12-01-13: Charles1dad
Agree with Elizabeth's point, actual use (practical application) is the final determinant. Rlb61 you were right to trust what you heard and not what theory would predict as the outcome.

While I certainly agree that in general actual use is the ultimate determinant, and supersedes theory if the two are in conflict, in this case it seems to me that it is not theory that is wrong, it is the THEORISTS that are being referred to who are wrong, or perhaps are being misinterpreted.

Specifically, it would appear that the alleged theory overlooks the fact that using the adapter may call into play a significantly different output stage design in the preamp. Which in addition to having different intrinsic sonic characteristics may also be interacting differently with the power amp's input impedance.

As I said in my earlier post, the OP's findings are certainly plausible from a technical standpoint, but a precise explanation cannot be provided without knowing more about the specific designs.

12-01-13: Cerrot
It is not uncommon to see different output voltages for the different outputs in specs.

Although often the difference in the two output voltages will be a factor of two, and that difference will be negated when an adapter is used, since as I indicated earlier the use of an adapter results in only one of the two signals in the balanced signal pair being utilized.

Regards,
-- Al