Lots of info/first hand experience on WBF:
'I spent my weekend playing the SUT match-up among the 3 SUTs that I have: Kondo SFz, AirTight ATH-2 Ref, MSL 1030.
I have a previous generation SFz with 3 levels’ of load imp, 1.5ohm, 3ohm, 40ohm with 36db, 30db, 20db added respectively.
AT ATH-2Ref offers 2 levels: 2ohm and 40ohm with 29db and 23db added.
MSL 1030 offers 1 option: 26db
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Bordeaux outputs 0.25mv gain, theoretically, the best is to boost it up to a 5mv-7mv range, hence an amplification ratio between 20x and 35x makes sense.
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In terms of load impedance, Bordeaux is a 3ohm cart. Classically, a 30ohm to 45ohm load impedance seems to be proper.
If we take the 1 and 2 as criteria to find a matching SUT, among the ones that I have, the 3ohm SFz gives me 31.6x ratio and a load impedance of 47ohm, the ATH-2ref at 2ohm gives me 30x ratio and 52ohm at the load impedance. Both seem to be in a good range.
To cut the back-n-forth comparisons short, I find the results prove the theory. The above 2 options work best for Etsuro Bordeaux in my system.
I loaded the SUTs into my Kondo M7 mm phonostage, with 46db gain, which is on a high side. It works well with my Dartzeel preamp, which I found with a relatively low gain at the input stage.
Both ATH-2Ref and SFz can bring the beauty of Bordeaux, on SFz even more so, maybe due to its all silver wiring. The tone is rich and lush but not excessive. Some posts reported that Bordeaux may sound a bit too much on the mid-range. I found the same if I load it into a different impedance, say 26db or 23db alike. That gives a load impedance at about 117ohm and 240ohm which seems to be too high for a 3ohm cart.
It is interesting that the Etsuro SUT is with 26db, 20x ratio. This is the same as the MSL 1030 SUT that I have. But the MSL 1030 didn’t give me a good sound. It sounds a bit muddy and makes the mid-range a bit too much boom. It doesn’t mean Etsuro SUT would be the same. But at least, I found the load at about 50ohm at the SUT works best for me.
SFz gives better highs, more airy and textured. ATH-2Ref is a bit more calm, a bit deeper in the bass. Both are very enjoyable.
I loaded the bordeaux directly into Soulution 755 MC, found it better loaded at 100ohm at a high gain level. But it doesn’t match the performance of an SUT to a cheaper Kondo M7.