I think it would be tough finding the Aesthetix for $2K. You should definitely consider the Schiit Freya which is under $1K new.
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Are you looking for a fully differentially balanced preamp - from input to output? Many tube preamps (including the Backert) with balanced outputs are either a hybrid design or use transformers, so they are not truly differential. Maybe you could reconsider this criteria unless you think it is somehow mission critical due to grounding issues or long cables runs for example. It opens the door up to many more possibilities, especially within your budget.
The Calypso’s balanced output impedance (measured by Stereophile to be 112 ohms at 1 kHz and above but a very high 3900 ohms at 20 Hz) is marginal at best with respect to the balanced input impedance of the XA30.5 (spec’d at 30K and measured as 29K by Stereophile).
The LS17SE as well as most other ARC line stages don’t provide a lot of margin either, having a recommended **minimum** load impedance of 20K. And it isn’t clear if that recommendation applies to its balanced outputs or its unbalanced outputs or both.
Finally, I agree with some of the others that you are unlikely to find a high quality fully balanced preamp meeting your various requirements for $2K used. And a preamp in that price range providing balanced outputs while having an unbalanced internal signal path might sound better if you were to use its unbalanced outputs and drive the amp single-ended. Note, though, that Stereophile measured the unbalanced input impedance of the XA30.5 as being 20K, so if you were to do that you would want the preamp to have an unbalanced output impedance of no more than about 2K at all frequencies.
Good luck. Regards,
If you could score a used Audio Research LS25 you'd be golden. All the inputs can be used as balanced or single ended, you set them at the front. The outputs are also single ended or balanced. The preamp is balanced from input to output, each phase has it's own gain path. It has a 0 gain processor bypass but the preamp has to be on to use it. An LS26 or 27 is newer but it might cost more than you budgeted.
As far as output impedance is concerned in practical use any load over 15k is fine, 10k is probably OK. I've used mine to drive an X350 and an Adcom GFA5802.
Thank you everyone for your advice. I appreciate it very much.
I took the plunge on an aesthetix calypso, paid $2160 all in.
I was also concerned about the impedance mismatch between the preamp and xa30.5 per the stereophile measurements.
However, listening to the combination now, I feel I am getting stronger bass with the calypso connected, compared to driving the xa30.5 direct with the m2tech young dac's internal preamp.
It could be that the speakers I am using, Focal Diablo Utopia, does not go down to 20hz where the output impedance from the Calypso hits 3900.
It could be also that there have been circuit board revisions since 2005, when stereophile posted the review, that have fixed the wide ranging output impedance problem.
Overall, it did introduce the tubey sound I am looking for, but not enough. Will be ordering some NOS 5751 RCA tubes to see if I can get an even warmer sound.
Once again, thank you everyone for your advice.
As a past owner of the Aesthetix Callisto signature, I am well aware of the tubey sound you are likely after. And with a local friend who had an updated version of the Calypso, with Mullard 10M tubes, the Calypso was not even close to the Callisto in terms of the magical 3D brought on by tubes. My Callisto was running regular Mullard and Tele 12ax7 and 6922. We did the comparison in my system and later in his. In fact, the Callisto exceeded the Calypso in every way.
So much of this has to do with a tube power supply. You can try tube rolling, and I'm a huge fan of this, but this will sadly only take you up a slight marginal improvement and little of that will relate to the bloom you're likely after.
The only products that I am aware of that fully meet all of your requirements start at the $3500 or so level and even then more likely at $4500.