Phono Pre-amp with XLR

Wolf_garcia ALL phono cartridges *are* balanced, and any MC is also considered low impedance. But you knew that, right?

Wolf_garcia, surprisingly (to me anyway), no, 'we' collectively don't seem to know that, even though that is the fact of the matter.

I say this because when we introduced the MP-1 22 years ago, it was the first balanced line preamp made. The fact that it is balanced line and not single-ended has been its biggest marketing problem: audiophiles and dealers alike have had problems with the idea that balanced lines are inherently superior in every way. One of the biggest superiorities, IMO, is the simple fact that if you do the balanced line properly, the cable no longer has to be expensive (that is why you will find me recommending Mogami Neglex cables in other threads).

We (rather innocently and also rather naively) assumed that audiophiles would be very interested in a technology that offered immunity to cables such that a $0.10/foot cable could sound as good as one that is $1000.00/foot. Boy were we wrong. Many audiophiles buy expensive cables for reasons that have nothing to do with audio: http://en.wikipedia.org/wiki/Veblen_effect

quote]However making a balanced amp is more expensive since you will need almost twice the components.[/quote]

It is more expensive but you do not need twice the components. Maybe 50% more if you are talking tubes, maybe not even that if you are talking solid state.

RCA jacks can be used as an input to a balanced preamp. How it works is that the RCA jack is isolated from the chassis ground, so that the 'ground' connection of the RCA can function as the inverting input to the balanced preamp.

There are some problems with this approach- you still have to use a ground post, perhaps no problem if the ground connection is supplied. However, the interconnect between the tonearm and the preamp **must not use the minus (-) output of the cartridge as a shield for the plus (+) side!** This would result in hum.

Now assuming that such a cable issue is dealt with, you still have the problem of the fact that at the RCA connection itself, the 'minus' (inverting) connection is shielding the 'plus' (non-inverting) connection. This damages the overall Common Mode Rejection Ratio of the system; IOW, it makes it susceptible to hum.

You can set up the RCA so only one of the inputs of the preamp is driven and the other side is at ground, but again the CMRR of the preamp is not available to the user, although you don't have some of the hum susceptibility of the scenario in the prior paragraph.

So, on a very practical basis, the XLR is a superior connector. Any use of the RCA for a balanced connection is a sort of kludge approach.

Tdaudio, if the preamp is differential, but you only drive one input, perhaps the non-inverting input (with the other input being tied to ground, where the minus output of the cartridge is also tied), the gain will be exactly the same as if you were driving both inputs, assuming the source to be the same cartridge in both cases. What you loose is the cable immunity (tonal neutrality) and rejection of noise in the cable.