RCA to XLR adapters?

The amp should not care if the input is balanced or single ended.

You will not get the benefit of a balanced preamp, but it will work fine.

First the XLR output/input voltage is twice that of rca. Second XLR uses differential op amps to cancel noise where rca does not have that feature. Will it work?? YES it will but you will not get all the benefits that XLR has to offer. Remember that XLR was originally designed for commercial purposes (ie long cable runs of 20 to 100ft) hence the doubled output voltage and noise cancellation circuitry.

That being said right now I am demoing balanced vs rca interconnects (same make - model and length) and although I like the XLR connection and if I listen very closely I can hear a slightly wider soundstage. That's it. I prefer rca's for 2 reasons. 1 The gain from XLR is too much (1 meter cables). 2 rca is virtually an industry standard and should I ever go back to all rca I won't have to have the cable re-terminated due to more equipment being rca only (especially reasonable price stuff).

You cannot get the advantage of balanced with a 2 wire cable .

Ralph (Atmasphere), one of the excellent papers at your site describes two of the fundamental advantages of fully balanced internal design, for power amplifiers, as being cancellation (or at least substantial reduction) of some distortion products, and presentation of an essentially constant load to the power supply. Won't these advantages be negated if a single-ended signal is put through a balanced amp?

Also, the benefits that a balanced interface provides in terms of reduced susceptibility to ground loop issues, and rejection of common mode noise, will be negated if an adapter is used, respectively because the signal return path will not be isolated from inter-chassis noise currents, and because of the impedance imbalance between each of the two legs and ground.

The two benefits relating to balanced internal design, I believe, can be retained if you were to choose a fully balanced power amp that has rca as well as xlr input connectors. I would expect that in those cases the input stage into which the rca input is fed would perform a single-ended to balanced conversion, resulting in a balanced signal being processed internally.

All of the benefits described above can be retained if you were to use a Jensen transformer between the preamp and power amp, to perform a single-ended to balanced conversion. See this paper. Note, btw, that the adapter cable shown in Figure 2.1 of the paper is NOT configured in the same manner as an rca cable + rca-to-xlr adapter, and the latter will provide considerably poorer noise rejection than the already degraded noise performance that is shown for the adapter cable.

A lot of users here have reported successfully using Jensen transformers in this kind of application with excellent results and no noticeable adverse effects, although I recall Ralph expressing some mixed feelings about them.

Best regards,
-- Al

Won't these advantages be negated if a single-ended signal is put through a balanced amp?

No. As soon as the signal is in the amp, it will be in the balanced domain if the amp is really balanced.

Using a Jensen may not be a bad idea- you have the SE preamp drive the Jensen, and then run you balanced interconnect as far as you need to the amp. I've done that a lot and its always worked well.