Advice on SUT for Koetsu Rosewood - EAR MC-4, Slagle/EMIA, other

Ralph, you would think the transformers would be designed for a 47K load which is pretty standard for MM phono stages. If not 47K how would you figure out what it was? Just a meter? Also why the capacitor. Wouldn't just a resistor do? I know you might have to change capacitive
loading for a MM cartridge but why the transformer?

@mijostyn They are designed for 47K, but any transformer designer worth his salt knows that the transformer isn't going to work perfectly with that- and that it will also change depending on what cartridge is used. IOW they know that it has to be loaded correctly (if they don't, they are leaving performance on the table). The capacitance has to do with the fact that you will likely get a peak somewhere that might not show up from simple ringing of the transformer with a square wave.


@montaldo If you don't get the transformer loaded correctly, you will hear differences but they won't tell you anything about which transformer is better! On top of that 20:1 is very different from 8:1.


To get to the right loading values for the transformer you have to talk to the manufacturer of the transformer. The only way I know to do this empirically on the bench is to  apply a square wave in series with the cartridge and look at the output of the transformer on an oscilloscope and vary its load to get a very slight amount of overshoot.


The problem here is that the capacitance of the tone arm interconnect cable is a variable, as well as the capacitance of the cable at the output of the square wave generator, and you run the risk of damaging the cartridge by deguassing it.


This is why I like working with Jensen, as they have demonstrated over and over again that they know and care what they are doing. Most SUT manufacturers can't tell you how the unit works with every cartridge out there.

Ralph, Sowter offers different step up ratios and tells you what cartridge impedance range the transformers were designed for. Is that enough in and of itself to get you headed in the right direction? I have installed them in the past and as far as my ears can tell they worked fine.

Ralph, I will ask Dave Slagle what he thinks about my setup and loading. The original sound tradition Hashimoto hm-7 I tried had an even higher winding ratio such as 1:30 I think. It sounded pretty amazing with 29dB gain. But it was a little too big and "in my face." This will be 26 dB on top of 46 dB of my linestage, which seems reasonable.

As fas the loading issues I still don't understand all those variables so I will continue to listen to you guys and talk to Dave Slagle as well.

@montaldo I have a diy SUT with Jensen AT 347 trannies.  These can be wired for 8:1, 12:1 and 24:1 gain.  I run a Dynavector XVT-1s at 24:1 into the MM of a Zesto Andros 1.2 phono pre.  You might want to ask Berning if your trannies can be rewired to 12:1 which should be enough of your cart's output..  That being said, not sure what is the MM gain of your unit.  If you go to the Jensen site, you can see the schematics for the three different gains.  The loading will not have that much impact on gain but it definitely helps to experiment as it relates to the sonics.  I used the zobel circuit that Jensen recommends for the 347 at the gain used.

Barolobrain: Firat of all you may need to explain your username to me (expiring minds want to know).
Second,  I did not realize these Jensen Transformers had optional configurations. If I could have mine required to 1:12 or 1:24 that would be interesting to try. Is the procedure difficult or could any tech do it, with insrtructions from Jensen?