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? 



Hi @pindac ,

I’m agree that EAR834p has rich and bloat the lowest frequencies character. This character of the schematic remained despite improving bass resolution and dynamics, and more clean and open height frequencies in the better implemented version. Another factor are speakers. My Altec 604E speakers have dry bass. So it works good all together at least for my taste and for classical and jazz music that I like to listen.
But I can’t agree that all SUTs have the similar sound characteristics. I heard SUT in my system that have thin sound. And in my experience, the difference between different SUTs is huge.



I don’t know that the method by which a signal is transmitted in a transistor is any better than a transformer

A FET works more like a valve/tube.
If you like transimpedance (current based) amps, they are more than likely a BJT.

The problem you are up against using either device above is that the input side of the device is outside of the feedback loop. You will have a rather prodigious electrical peak, likely between 1-5MHz with most LOMC cartridges. It might be as much as 30dB depending on the Q value (how long as opposed to how wide) of the coil in the cartridge. That peak can be energized and easily overload the input despite the use of feedback.

So an SUT has the advantage of not being overloaded in this way and actually blocks the RFI generated in this fashion from reaching the phono stage input! That's a pretty clear advantage!

(The overload can cause ticks and pops as well as distortion which is perceived as brightness- hence the use of 'cartridge loading' resistors, which detune the electrical resonance, preventing it from going into excitation.)

If you're going to run solid state, you need to use an opamp to get around this problem, or set up the feedback look on the discrete devices in the same manner as used in with an opamp; essentially creating a low performance opamp in the process...


Hi @atmasphere ,

I have a question for you regarding the use of feedback in tube phonostage. Unlike a power amplifier, the frequency response of the RIAA implies a deeper feedback at high frequencies. Is this kind of feedback deep enough to work properly?



Unlike a power amplifier, the frequency response of the RIAA implies a deeper feedback at high frequencies. Is this kind of feedback deep enough to work properly?


If in a discrete solid state circuit, maybe?? -a lot will depend on the semiconductors involved!! It can work OK with tubes, but if you really want to get it right, you run the amplification flat and use passive EQ. That way you can apply the feedback needed to do the job right.

Dear @drbond  : " would also logically favor an integrated pre-amplifier / amplifier over separate components, "


Not really, I am in favor that the amplifier stays as nearer the speaker as we can and that's why I use monoblocks with really short output cables that are soldered directly to the speakers external modified crossovers  where each speaker driver frequency range has its dedicated crossover/cable that goes soldered directly to each driver.


No, what I'm in favor is for a Phonolinepreamp unit but separates amps.