SUT Advice - Which Ones Are The Best?

JCarr, thanks again for yet another great help to SUT users. The only SUT-maker that I have dealt with personally are Jensen transformers in California, and yes those guys really know what they’re doing and what they are talking about, and they offer extensive information on how to use their products. I am sure the same must be true of the other companies that you have named specifically.

Edgeware, I am puzzling over your saying ..."the Denon has only 21dB gain and not suitable for low impedance cartridges,..." First, 21 db of gain equates to a voltage gain of about 11-fold. So, it would provide more than adequate voltage gain for any LOMC with at least 0.4 to 0.5mV output, to drive a typical MM phono circuit with at least 40db of intrinsic gain. I don’t understand why you say it is not suitable for cartridges with low internal impedance, unless you know something about the inductance of the primary winding of the Denon, per the post by JCarr. With a typical MM input providing a 47K ohm load resistance, this Denon SUT would present the cartridge with about a 400 ohm load. Certainly that is OK for any LOMC, notwithstanding the issue of primary inductance. I actually think there is a bit too much hocus pocus surrounding the mating of a SUT to a cartridge on one side and the phono stage on the other. What you need to worry about is the voltage gain, which is related to the turns ratio of the SUT, the impedance seen by the cartridge, which needs to be about 10X or any ratio greater than 10X that of the internal resistance of the cartridge, and the inductance of the primary. Keep in mind also that a transformer essentially has NO impedance of its own; it only reflects an impedance from whatever is hooked to the secondaries back to whatever is hooked to the primaries, and vice-versa. In my opinion, the old custom of rating SUTs in "ohms" seems to be very confusing to a lot of people and really should be abandoned because it is not even informative. And finally, using a SUT gives up current in direct proportion to the voltage gain it affords. The product (voltage X current) is a constant on one side vs the other. If V goes up 10X, then current goes down 10X.

Mijo, Why are your wanting me to read about Sowter SUTs?

A coil inevitably has inductance. However there are some tricks of winding that can minimize it, as in Mills resistors. Otherwise wirewound resistors are inductive. It’s the law.

JCarr, thank you for the erudite post. For most of us, the needed gain is easily estimated, and the internal impedance of the cartridge is available from the maker, but I know of no instance where the primary inductance of the SUT is accessible to the end user. How does one acquire that data point?