SUT vs. Phono Preamp?

Vinylcafe

Vinylcafe

Linvin' the Dream
Right now I am using a Clearaudio phono preamp.
I can load it however I want.
My MC cart sounds good with a 1K ohm load, and then goes to an Aux input.
If I use a SUT into my MM phono input, I will get the default 47K load for an MM cart.
Any way around that?
Is my assumption correct?
 
And a Phono Head Amp gives the best of both worlds. It doesn't have any RIAA equalization so you input to a phono stage, but you have adjustable loading and gain.
 
Vinylcafe said:
Right now I am using a Clearaudio phono preamp.
I can load it however I want.
My MC cart sounds good with a 1K ohm load, and then goes to an Aux input.
If I use a SUT into my MM phono input, I will get the default 47K load for an MM cart.
Any way around that?
Is my assumption correct?
Click to expand...

Not really. The effective load that the cartridge sees is reduced greatly by the ratio of the windings in the SUT. The practical effect is that loading matters much, much less, and for many popular combinations, seemingly not at all.
 
My experience with a Dynavector DV 6a SUT is that it clearly muted the high end sparkle or air in my system. I do know that the DV 6a is not as good as some that are out there, so the difference may be less on a better SUT. The Nakamichi MC and Phono section was dead quiet, and it seemed to position the instruments on the stage more clearly with better defined space between them.
 
I favor a quality SUT and have vintage Jensen and Cinemag 1254 SUT's in rotation. Also a Fidelity Research FRT-4 on the way ;)
 
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If the SUT is designed by the cartridge manufacturer then it should provide the optimum load to the cartridge with out any modification when connected to the 47 K load of your phono input.
 
On my Hashimoto SUT, resistive loading does have some effect. There are math formulas out there to calculate the load a cart will "see" from the combo of the SUT transformer windings ratio and the MM/47k ohms phono preamp.

For example, a 15x ratio SUT into a MM/47K ohm phono preamp will give you 208.9 ohms seen by the MC cart (47,000/15/15) and a 30x SUT will give you 52.2 ohms seen by the MC cart. In theory, because you have to account for insertion loss, etc.

Adding resistor's in parallel can REDUCE the resistive loading seen by the cart.
 
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edwyun said:
On my Hashimoto SUT, resistive loading does have some effect. There are math formulas out there to calculate the load a cart will "see" from the combo of the SUT transformer windings ratio and the MM/47k ohms phono preamp.

For example, a 15x ratio SUT into a MM/47K ohm phono preamp will give you 208.9 ohms seen by the MC cart (47,000/15/15) and a 30x SUT will give you 52.2 ohms seen by the MC cart. In theory, because you have to account for insertion loss, etc.

Adding resistor's in parallel can REDUCE the resistive loading seen by the cart.
Click to expand...

This is really interesting, and the first time I've run into this formula.
Does that mean the quality of sound produced with the SUT will be the same as of phono stage loaded with a 200 ohm resistor (using the above example).
Reason I ask, my Benz Micro ACE S-L likes at least a 1K load; at least to my ears.
200 ohms would sound a little lifeless.
 
Vinylcafe said:
This is really interesting, and the first time I've run into this formula.
Does that mean the quality of sound produced with the SUT will be the same as of phono stage loaded with a 200 ohm resistor (using the above example).
Reason I ask, my Benz Micro ACE S-L likes at least a 1K load; at least to my ears.
200 ohms would sound a little lifeless.
Click to expand...

Actually, it should sound better with the SUT. ;)

Generally, you first pick a SUT to provide sufficient gain (along with your system's other gain devices) to drive your speakers properly without distortion. That's the SUT's primary purpose as a passive device. That should be sufficient to get good sound. But to go the extra mile, IMHO, it is good to adjust the setup to get the MC to "see" the load resistance somewhat near what is recommended by the manufacturer. This can be done in some cases, for example, by using a parallel resistor at the input to the phono preamp.

I am testing this currently in my setup. I'm using a Dynavector 20x2L specified at 0.3mV output, internal resistance of 5 ohms, and recommended load resistance greater than 30 ohms. From my and others' experience, I know that the 20X2L typically works well with a load resistance between 50-150 ohms. Before adding the SUT, I was running it at MC/100ohms into my phono preamp and all was good!

Using my SUT at the 15x setting into my MM/47,000 ohm phono preamp, the MC "sees" about 208.9 ohms (47,000/15/15). To get the MC to "see" about 123.5 ohms, I can add about a 68,000 ohm resistor in parallel. To get the MC to "see" about 81.4 ohms, I can add about a 30,000 ohm resistor in parallel. Some math (oh no!):

Say I want the MC loading to be about 81.4 ohms on my 15x SUT, so...
81.4 ohms = X/15/15
(solve for X)
X= 18,315

Then to calculate the value of parallel resistor I need into the MM/47,000 phono input to get the 81.4 ohms...
Resistor = 1 / ((1/18,315) - (1/47,000)) = about 30,000 ohms.

With loading in this sweet spot (50-150ohms), I notice the SUT seductive qualities a lot more. It's a siren that beckons. YMMV.

Not sure if there are any SUTs out there where you can get or reduce the loading to 1K, though. But first thing is to get the proper gain with the SUT as I said earlier.
 
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Thanks so much, really useful info!!
I am going from a phono stage to a 15:1 SUT, as I really like the MM phono stage of my preamp, and want to use it.
I will try loading the MM input with some resistors in parallel, and see the sound differences.
 
The 15x SUT will not likely be able to get you to 1K ohm loading on your MC with a MM/47k ohm phono preamp. Parallel loading can only REDUCE the resistance from 208.9 ohms (based on the 15x ratio).

Changing the resistance in the phono preamp from 47k ohms is something else.
 
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I purchased 3 SUT's to compare. I have a HK, SUTMAN built one and an AT630. To tell you the truth I like the sound of the AT-630 best and it was 1/3 the cost. I have only ran LOMC and a tube MM phone pre. So a SUT is needed. I have only tried one high output MC and I wasnt taken by it.
 
Please have in mind that all transformers have ferromagnetic materials inside their core. That material is there to "amplify" the magnetic field generated by the coils, that is usually very small. There is a price to pay, though. No material has a behavior that is flat throughout 3 orders of magnitude in frequency range (i.e., the usual audio bandwidth from 20 Hz to 20 kHz). So, there are non-linearities introduced by the unavoidable use of a ferromagnetic core. Of course, material choice, construction design and other topics may tame those variations, but it is useful to have in mind those effects. This is to say that all SUTs introduce solo "coloring", that may be pleasing to some people, as with the usage of other technologies. What about phono preamps? In principle also these devices could introduce some coloring, but the control of linearity in a small power amplifying device is greater, in principle, if the circuit design is good enough.
 
Talking about personal experiences, I´ve never heard anything better than my Sonneteer Sedley phono preamp, that is within my humble exposure to gear and devices. Definitely, none of the SUTs I´ve ever tried (I still own a Ortofon matched for a MC20 cart) gave me such even listening pleasure. But again, regarding LP playback, there is no limit to the sophistication and costs of the devices sold in the market. The argument I´ve made above is about physics and not regarding listening expriences, but is is, nonetheless, an objective rather than a subjective argument against the use of SUTs that belong to the realm of previous technologies. But again, many people pefer the sound of vacuum tube amplifiers and the variety of opinions and tastes is of course all for the good in this as well as many other subjects in life.
 
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