Using XLR for Phono out

Lewm, if you feed a balanced signal to a transformer and the primary winding is either "floating" or wired balanced (CT grounded), you will have CMR even if the secondary is wired SE. If the signal is the same on each leg of the primary (common mode) the potential difference is zero! No magnetic flux, no signal transfer, therefore high CMR. The primary does not care how the secondary is connected as far as CMR is concerned.

Cool. But I was not totally wrong; you need to feed a balanced signal to the primary. I don't know why one would want to convert a perfectly good balanced signal to SE, except if you are a transformer-phile. (I'm just kidding; you probably have sound justification for this approach.)

Manufacturers do it because SE is cheaper (half the number of parts ;-) ). In phono preamps, designers have traditionally used SE architecture because adding the other half for balanced will increase the inherent circuit noise. That would be a good example. The MC pick-up is naturally balanced. Connecting it that way to the primary of an MC input transformer, then connecting the secondary SE is quite common.

John (12-19-09),'a potential fly'. In the context of (ASR)
Basis Exclusive I mentioned the recommendation from Schaefer (ASR owner) to use RCA out when using balanced inputs. Alas I was not able to explain the issue. But your
statements regarding the OP amps may explain the 'actual fly' in connection with Basis Exclusive?
Regards,

John_tracy, just for the record, to do things balanced does not double the parts (its about 50% more) and the noise is actually **lower** for a given stage of gain, not higher! The noise is theoretically 6 db less per given stage of gain; this can really add up over several stages so when you are done, you often can get by with less gain stages overall.