Long distance between preamp and power amp

Dentdog, I don't see any issues with what you've described.  In fact the design of the Leto seems ideally suited to a situation involving a lengthy connection to an unbalanced input.

John Atkinson's measurements of the output impedances of the Leto were even lower than specified, and as I'd expect in the case of transformer coupled outputs did not have much variation as a function of frequency.  That will make the capacitance of the long interconnects a non-issue for any reasonably designed cable. 

Also, I don't know if you are using RCA cables or XLR cables + adapters to mate with the unbalanced inputs of your MC60s, but either way you are in effect running unbalanced interconnections since the load is unbalanced.  However given the transformer coupling and the provision of ground lift switches in the Leto for its unbalanced outputs you presumably are immunized from ground loop effects that can occur in some cases involving long unbalanced interconnections.

Also, actively driven balanced outputs on some equipment (as opposed to transformer coupled outputs) may have problems with XLR-to-RCA adapters, since most such adapters short the signal on XLR pin 3 to ground (XLR pin 1).  But again that won't be a problem with a transformer coupled output, and in some cases involving transformer coupled outputs it may actually be necessary for an adapter to connect those pins together.

Enjoy!  Regards,
-- Al
 

I couldn’t find an output impedance spec on the C712, or anything that would provide an indication of how its balanced outputs are generated. But given that it is a solid state design chances are its output impedance is relatively low. And given that all of the input connections it provides are unbalanced, chances are that one of the two signals in the pair of signals it provides to its balanced output, for each channel, is generated by putting the other signal through a simple op amp stage, ca. 1995. Which in turn suggests that the C712’s unbalanced outputs stand a good chance of providing better sonics than its balanced outputs.

Given those considerations, I would suggest simply using an RCA cable having relatively low capacitance, less than say 20 pf per foot, and providing good shielding. Blue Jeans LC-1 meets those requirements at a low price point.

I suspect that will work out fine. If not, though, a Jensen transformer can be considered, as I mentioned earlier.

Also, FWIW, personally I would much prefer to replace the preamp and/or add a Jensen transformer than replace your amplifier, which is a treasure based on all of the user comments I have seen about it.

Good luck. Regards,
-- Al

There’s no reason to consider selling such a fine amp. If it proves to be necessary you could connect a suitably chosen Jensen transformer (ca. $275) between the preamp and the amp (close to the amp), to convert balanced to unbalanced. That would provide essentially all of the benefits of a balanced connection.

But it may very well not be necessary. What is the make and model of the preamp?

The approach that is best may very possibly depend on several different characteristics of the preamp. Including its output impedance; how its balanced outputs are generated (and therefore whether the sonics of its balanced outputs are likely to be better than, worse than, or similar to the sonics of its unbalanced outputs); and its internal grounding configuration (that may affect susceptibility to ground loop issues, which can be brought out by long lengths of unbalanced cables).

Regards,
-- Al