ZYX Airy 3 Best SUT

The Airy 3's output is actually higher than .24mv if industry standard test tracks are used. ZYX uses a less commonly known test LP to measure output, one which results in lower numbers. Multiply by about 1.34 to get an output that's comparable to most other carts... ie, around .32mv.

ZYX's impedance spec of > 100 ohms is when using an active gain stage. That figure is irrelevant for stepups. Many years ago I did the math and then carefully optimized our Bent Audio stepups for Airy 3 and later for UNIverse. It took a lot of trial and error, as the tiniest resistor changes were audible. Calculations are lost in the depths of time but the Bent's ability to easily swap resistors was very helpful.

Even better would be a design that lets you swap resistors on both the primary and secondary windings to control resonance peaks in both the cartridge and the tranny (Zobel network). Truly matching an SUT to a particular LOMC requires a lot of work, not to mention a fair sized pile of resistors.

All that said, one of the best, untuned SUTs I ever heard with a ZYX was a friend's Cotter. If you come across a used one it would be worth buying.

I have the same cartridge and use the Auditorium 23 sut that is ostensibly maximized for Ortofon SPU carts. It is a perfect match. Have also used lundahl/k&k audio sut's and jensen sut's as well as an inboard shindo sut in a Masseto preamp, but the A23 sut really really works well with the zyx.
As an aside, my K@K sut had resistors to vary the loading, but the A23, albeit at a little more than twice the price, bettered it without any resistors to monkey around with.

Thanks Bnrlaw
This sounds perfect. I did not want to mess around with resistor loading.
Thanks again for the advice.

Doug, very interesting info on the output of Zyx. I happened noticed not by measure but by listening, Zyx Univ. (.24mv) is actually higher output than A90 (.27mv), since you mentioned a factor of 1.34, it makes sense.

I think to achive the best sound with Bent MU for Zyx 4ohm is to use 1:20 ratio, not 1:10. By design, S&B TX-103 on 1:10 is only good for cartridge with over 10ohm DC impedance not lower, info available on S&B website. If setup TX-103 on 1:10, no matter how hard to try on various loading, the result will always be less optimal. In the case of Denon 103, given it's relatively high DC impedance, only 1:5 ratio should be used on TX-103 which will defeat the purpose of a step-up.