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

Thank you Atmasphere! the Berning preamp has loading plugs for the moving coil section but if I understand what you're saying correctly those are for the INPUT side whereas you think the Jensen transformers themselves may need loading on the output side. Is that correct?

I can't speak to the Berning as I'm not familiar with its innards but to the last question, any and all SUTs should be loaded on the output side and the cartridge should never be loaded at all since the SUT is doing all the loading via its ability to transform impedance. So when its loaded correctly (with the cartridge at its input) there is simply no need to load the cartridge.

As an additional note, cartridge loading is for the benefit of the preamp not the cartridge. If the preamp has good RFI immunity no cartridge loading will be needed. When the SUT is used, it blocks RFI generated by the cartridge inductance and tonearm cable capacitance, so no need for cartridge loading. Clear as mud? 


An additional note: the amount of gain you ask of a transformer also degrades its performance. So the least amount of gain you get from it will always be the best. Also, if you use a different turns ratio the correct loading will change.


Until you are able to sort out this loading issue, its quite pointless to compare transformers!!! Some transformers are designed to be fairly well loaded when presented with a 47K load and a nominal cartridge resistance, others are not (IMO Jensens fall into the latter category; they assume that you are going to pay attention and get the loading right). In a nutshell you would then be comparing apples to oranges. Any SUT comparison needs to have the SUTs on an even playing field; both need to be properly loading which will not be the same values! The transformer manufacturer should **always** be able to to supply you with the correct loading values (which will usually be a combination of a resistor and capacitor).

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?

Mike 

Mike the the formation so far has been confusing at best.  You might be best served talking again to Dave at intact and call Kevin at K+K audio.  The ratio of the step up is squared then divided into the 47,000 resistor.  So 10 to 1 is 10x10=100 then 47,000÷100=470.  So the cart is seeing a 470 ohm load.  There are ways to parallel resistors to lower that value but not increase it.  The cap is use if you want a zobel network.  Some guys like others do not.  

If you really want total control with step up ratios and cart loading you need have your friend bypass the 47,000 and play with various resistors externally.  Then when have what you want you could replace the 47k with the new value.  If you sell the phono stage latter you could put back the 47k.

Without total control of the step up and loading you never really know what your cart is capable of.  And of course the transformers also have a sound of their own. 

Maybe Dave or Kevin will build you a sut box that you can plug in different resistors and easily change step up ratios.  Then bypass the 47k in the phono stage and you are good to go.

Enjoy the ride
Tom

 After after all our exchanges, which I appreciate so much, I decided an experiment might be useful. So I am buying a used Intact Audio 1:20 copper SUT to just try and see how different it sounds from my internal 1:8-ish Jensens in my Berning pre. I will report back this weekend.
Stu

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.