How to accomodate a balanced only phono stage ?

There is a long thread with digressions on this topic at

http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1172373006&read&keyw&balanced&&st50

Gain is not lost in single-ended vs. balanced wiring of cartridge, as the voltage output of the cartridge is what it is in either scenario. Some state that dividing this voltage across the two phases of a balanced amp may reduce s/n ratio. Others believe this is off-set by the advantage of common mode noise rejection in a differential circuit. Others state that the reduced capacitance that the amp sees from the source in a balanced hook-up may be advantageous.

Dave, Lew, thanks.

I haven't yet taken the time to go through the thread Dave linked to. But I would expect that a factor that would in some cases be decisive regarding the advisability or inadvisability of using an rca-to-xlr adapter which grounds pin 3 (as opposed to an adapter cable which does not) is:

IF the phono stage and part or all of the subsequent signal path and components in the system are fully balanced designs, then using an adapter which grounds pin 3, in addition to ruining common mode noise rejection capability at the phono stage input, will result in the sacrifice of some of the key advantages of fully balanced design in those subsequent parts of the system. Including cancellation in those components of some forms of internally generated distortion, and, particularly in the case of the power amplifier, reduction of power supply-related noise.

Also, if the entire signal path is balanced, a considerable fraction of the amplifier's power capability (as much as 75%) will probably become unavailable.

It should be noted, though, that grounding pin 3 and thereby in effect making the subsequent parts of the system single-ended in those respects, will NOT degrade the common mode noise rejection capability of balanced interfaces that may be present at points in the signal path subsequent to the phono stage input.

Best regards,
-- Al

Dgarretson has got it pretty close. The gain of the preamp is unaffected by using only one input single-ended; the problem with that is noise that is now available at the input of the preamp, whereas if you use the signal balanced, the noise can be rejected, and just as important, the input cable will have less artifact.

I am really impressed at the increase in knowledge in the community regarding this subject!! Only a year ago there would have been a lot more myth-information present on a thread like this, so far the only such posts have been two from one 'goner. Well done!

English is not my native language and I don't really know that much about cartridges. But if I were to buy a phono amp like the Blue amp Surzur, which to my knowledge is of a fully balanced design would I benefit from using XLR cables.
The junction box on my VPI scout can be replaced by a XLR junction box. Or should I just use RCA cables.

In addition does anyone have any experience with a blue amp Surzur?

Mordante, your best option in this case is to replace the junction box with one for XLR cables, and run everything balanced. The advantage of doing this is that the cables will have less overall effect on the sound- they will be more neutral.