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Choosing the right SUT for my setup


I’ve decided to add a SUT to my setup. My MC carts are a Denon 103R (14 ohms/0.25mV) and an Audio Technica AT-OC9XSL (12 ohms/.4mV). I’m trying to decide between two used SUTs: the Denon AU-300LC and the Denon AU-320, both having a 1:10 ratio. Would loading ideal gain for the 103R and the OC9 be best achieved thru a using a calculator and installing a resistor that can be switched for carts or testing with a trimpot then installing resistor? I’ve also seen writeups where the OC9 is put on a 1:12 SUT and 1:20 for the 103R; from the boards experience is that pushing overload, or its in a good spot?

jctyler

Showing 3 responses by dover

dover
2,187 posts
 

Forget about the loading - focus on gain required.

1:10 Transformer should see 470ohms at the cartridge which is fine for either cartridge.

If your phono has reasonable gain then 1:10 should be enough.

Spend the extra and get an AU340 if you can - its much better than the AU301/320.

 

dover
2,187 posts
 

SUT’s do not have universal loading, meaning that just because a SUT is a 1/10 version does not necessarily mean the cartridge will see 470 ohms. Here is an example, my Jensen mc-2rr-L has a 430 ohm impedance that the cartridge will see, while my Rothwell mcx SUT, also 1/10, presents a 100 ohm loading.

The only reason those specific 1:10 SUT’s present 430ohms/100ohms to the cartridge is because they have either a zoebel network or resistive loading that is reducing the load seen by the cartridge from 470ohms.

A 1:10 turns ratio SUT with no loading will present 470ohms to the cartridge.

dover
2,187 posts
 

 If you believe that cartridge loading does not matter, well then, forget it and be happy.

Yes - I have a raft of highly regarded SUT's - and have experimented with a variety of top flight cartridges - from 3-40ohms internal impedance.

What I have found is that the "sound" and quality of the SUT dominates no matter what loading as long as the cartridge is not loaded down too far  ( not less than 10x the impedance ).

In my view far more important is getting the gain right - finding the optimum gain for the phono stage/preamp so as you are not running the volume too low or too high.

Jonathan Carr has written on this forum - loading only really impacts the sound if there are issues with the ensuing phono stage. Loading does not change the "sound" of most modern moving coils. Therefore if a SUT presents 470ohms say to a low impedance cartridge, for example koetsu @ 3ohms, it doesn't really matter.

For those who hear a difference - there is a problem either with the phono stage or arm/cartridge issue.

For what its worth my reference system uses a current sensing MC step up into a tube phono stage, which I prefer to SUT's into same. Doesn't mean you can't get a great result with SUT's.

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