Why do most phono preamps lack XLR input even thought cartridges are naturally balanced?

oldears

...the specs for my Ayre P-5xe: the gain for the balanced output is 6 dB higher than single ended out for each of the 3 gain selections. However the gain does NOT change with the choice of RCA or XLR inputs ...

Thank you! Exactly. That’s been one of my points from the beginning of this thread; the choice of connector has nothing inherently to do with whether the circuit is balanced (or not) or differential (or not).

And one of the best places to use differential circuits is in the phono section, for both higher gain and better immunity to noise.

roberttdid

Except with a phono input, you don’t gain 6db, as it is an application specific input. It amplifies the difference between the two leads. There is no "differential" output that has 2x the signal level (6 db).

I do not know what you mean by "application specific input" or why this matter isn’t more clear to you.

My phono preamp gain is adjustable and is spec’d up to a maximum of 68 dB single ended and 74 dB balanced. That seems consistent with my experience.

roberttdid4

As a counter to that cleeds, and not taking anything away, it is also true that because an RCA connection is used, does not mean that the input is not true differential ...

Quite so, and I made that same point earlier in the thread (fifth post). The Audio Research Ref Phono preamps are examples of RCA connections into a differentially balanced preamp.

... differential gives you the ability to increase gain while decreasing common mode noise, but you are still amplifying differential noise as well as noise internal to the amp. You are not getting 6db for free.

That's a fair point. There's no such thing as a free lunch. It's still 6 dB.

You could always crank the gain 6db on a single ended connection ...

Actually, no you can't "always" - unless you change preamps. At maximum output you do gain 6 dB with a differential circuit.

danvignau

There is little, if any, advantage to XLR on short runs.

That’s a pretty broad statement and it isn’t clear exactly what you mean. As I’ve already pointed out, the use of XLR connectors does not necessarily mean that the unit is true differentially balanced.

There is great potential advantage in using differentially balanced circuitry and connections in a phono preamp. In addition to the increased immunity to noise, there’s a 6 dB increase in gain. That’s a huge advantage in a phono section!

As @lewm notes, that a phono preamp has XLR inputs doesn't necessarily mean that it is fully balanced. But the inverse is also true - there are differentially balanced phono preamps that use RCA connectors. ARC Ref Phonos, for example.