SUT - electrical theory and practical experience


Some vinyl users use a SUT to enhance the signal of the MC cartridge so that it can be used in the MM input of a phono stage.  Although I don't understand the theory behind it, I realize that a SUT should be matched individually to a particular cartridge, depending on the internal impedance of the MC, among other things.  

Assuming an appropriately / ideally matched SUT and MC, What are the inherent advantages or disadvantages of inserting a SUT after the MC in the audio chain?  Does the SUT theoretically enhance or degrade the sound quality?  What does the SUT actually do to the sound quality? 

Thanks. 

drbond

@holmz 

But I’ll need to check the diagram to see if that built-in 1:4 SUT is loaded on the primary or secondary side

There are two possible loads that this SUT could have. The unintentional which is the typical 47kΩ input of a MM phono and the intentional which would be an additional filter on the secondary to "correct" any misbehavior of the device.   Both of these loads would be on the secondary of the device.  If there are specified cartridge loads for MC then is possible there could be an additional combination of primary and secondary loading and with the low turns ratio this is a possibility. 

I do think that the typical "dull" sound from loading a cartridge down too much is purely a function of the SUT behavior.  Since you have such a low ratio transformer an interesting experiment would be to find out the "calculated" reflected impedance and then try the following experiment.  (below I am assuming a 47kΩ load and a 40Ω Denon 103 and you can scale the values for different cartridge impedances.)

Assuming the 1:4 is terminated with 47kΩ  and a the cart should see 3kΩ as a load.  Now place a 1.6kΩ resistor across the secondary to reflect just under 100Ω to the cartridge and give it a listen.  Next remove the 1.6kΩ resistor and place a 100Ω resistor across the primary and listen again.  In a perfect world the load the cartridge sees will be the same (roughly 2.5X the internal impedance).  The gain of both situations will also be the same and my experiences tell me the sounds will be quite different.  To be clear... any differences heard will be a function of the SUT behavior and not the load the cartridge sees which puts this squarely in the purview of this discussion.

now that I am done with my airing of grievances it is on to the feats of strength.  Happy Festivus to all!

dave

Dave, I’m getting my Festivus pole out of storage now. I just aired my grievances with my wife. Then we’re going out for Chinese food.

Dear @drbond  : Yes, is more easy posted that way that give an answers that affect you because what I posted seems to me is true.

 

Ignore is your proble. Fine with me.

 

You have a huge problem that I posted in some of my posts: why with your CH are you asking so " deep " in a SUT other than buy one of same preamp manufacturer? This has no sense to me but obviously has a lot of sense to you that are not 100% satisfied with the CH. Maybe I'm wrong.

 

R.

Thought I share my perspective. In short, SUT’s are imo very cost effective and it easily gets forgotten. Some people have restrictions, for example room/placement and/or economical limits. Thats the case for me. 
Have Kenwood KD-990 (increased mass on tonearm) with Denon DL-103 for the past 25 years. Monitor audio speakers just as long. Standard gear all the way. 
Phono preamps have changed over the years though and also nowdays have a Denon DL-305. Started with cheapest Pro-ject stage and my last and to me most ”expensive” phono preamp was ASR Mini Basis. It was a nice sounding unit for sure, but there was constant noise from the speakers. Not too bad and didnt really notice it once the needle dropped but there was noise for sure. Decided to try a SUT instead, bought AU-340 and never looked back. I run the SUT to my Denon AVC-X8500 built in phono stage (I assume its crap!) still this is the best sound I had. Paid 350 USD for the AU-340, there is absolutely no way a phono preamp at that price would stand even the slightest chance against the SUT. So take this into consideration please. Also, maybe some people like fiddling around with dip switches and experimenting with loads etc etc, I did with my ASR but the whole thing just annoyed me at the end. 
I am about to buy a better MM phono preamp now. No silly money though, looking for something tops 500 USD. Any recomendations apreciated. 
Respect and thanks for a great forum that helped me a lot over the years.