Anyone know of these SUTs?

[alcarmichael]

http://www.ebay.co.uk/ulk/itm/171831924746

The guy will taylor make the SUT, selecting the transformer with suitable gain and then match your cartridges internal impedance.

I'm tempted to order one, wondered if anyone had any experience of them?

[Barry]

The transformers themselves look like they are made by Beyer Dynamic (http://technicalaudio.com/pdf/Beyer_Dynamic/Beyer_Dynamic_input_transformers_1976_oct_cat.pdf) , but the photo is not suficiently sharp to be able to read the model number (probably deliberate).

They look to be well made and reasonable value for money, but as I've commented before, the actual transformer chosen has to be matched to the cartridge being used. This affects not only the turns-ratio, but other details such as the resistance and inductance of the primary winding, and to some extent the interwinding capacitance and impedance of the secondary winding.

[dmckean]

It looks as though he sells 1:10, 1:15 and 1:30 versions. That should cover most of the LOMCs on the market. He also sells a 1:2 version for HOMC, which is something that I've never seen done before.

[alcarmichael]

The transformers themselves look like they are made by Beyer Dynamic (http://technicalaudio.com/pdf/Beyer_Dynamic/Beyer_Dynamic_input_transformers_1976_oct_cat.pdf) , but the photo is not suficiently sharp to be able to read the model number (probably deliberate).

They look to be well made and reasonable value for money, but as I've commented before, the actual transformer chosen has to be matched to the cartridge being used. This affects not only the turns-ratio, but other details such as the resistance and inductance of the primary winding, and to some extent the interwinding capacitance and impedance of the secondary winding.

I can figure out the voltage easy enough. My understanding is a typical MM cartridge gives an output of 5.5 mV. My cartridge outputs 0.35 mV so a ratio of 1:15 would bring me very close to the 5.5 mV target. With regard to everything else I'm lost. Can you help with choosing a transformer for my cartridge specs?

Audio Technica ART-1
Output voltage = 0.35mV
Frequency range 10Hz to 50KHz
Coil impedence = 12ohms
Recommended load using amplifier = min 100ohms
Recommended load using transformer = above 20ohms

[trio leo]

I've never tried a SUT, but my friend is a clever electronics guy and he swears by head amps, so that's what I use, it's switchable and it handles my cartridges beautifully, I'd like to do an a/b between a Headamp and a SUT, I guess if they are of similar qualities they would be a reasonable match, personal taste I suppose.

Enjoy your music :)

cheers Al

[Barry]

Hello Alex,

Apologies for the slow reply.

Certainly a transformer with a 1:15 turns ratio will transform the nominal 0.35mV of your cartridge to 5.25mV.

If you want to use a Beyer transformer, there will be some difficulty in arranging suitable loading for the cartridge. According to the Beyer data sheets, a 1:15 transformer has a primary DC resistance of 85 Ohm and a secondary resistance of 10.45 KOhm.

When the secondary winding is loaded by the nominal 47 KOhm of your phonostage, the impedance looking into the primary, that is the impedance seen by the cartridge, will be 340 Ohm. This might be too high. A general rule of thumb is that cartridges run best when they are loaded with ~ 10x the coil resistance, which for your cartridge is ~ 120 Ohm.

Now the primary resistance is 85 Ohm, so the transformed secondary impedance need only be 35 Ohm, implying an actual secondary impedance of 35(15 x 15) = 7825 Ohm. Yet the secondary resistance is already 10,450 Ohm, so it is impossible to achieve a 120 Ohm primary load.

What you can do is to leave things as they are and see if your cartridge is happy running into an effective 340 Ohm load. If you want to experiment with increased loading (i.e. a lower effective primary impedance), you could try shunting the primary winding with say a 200Ohm resistor to reduce the load impedance to 126 Ohm. If you choose this method, I would recommend you choose a high quality low noise metal oxide resistor, or ideally a Vishay Z-film resistor, though the latter are not cheap, they are the best you can get for this critical application.

If you want to use a Beyer transformer the appropriate model number is TR/BV 351 015006 or TR/BV 353 015006.

Ideally the transformer ought to located as close to your arm as possible, but at the same time the total capacitance of the cable fitted to the secondary ought to be no more than 100pF, that is 1 metre of typical coaxial cable. That way any HF rise ought to be < 0.5dB at 20kHz.

[helma]

I'm under the impression the DC resistances of the primary/secondary windings basically don't have anything to do with the impedance the cartridge will see and in a perfect transformer would actually be 0, while the load impedance the cartridge see will be solely determined by the step-up ratio (and phonostage input impedance of course) - at least this was what I was told by someone who knows this stuff far better than I do. A transformer is a device of two coils doing black magic and transferring the signal with all kinds of wizardy, inductance and magnetics and what ever, so poking the input RCAs with DC resistance meter won't really tell you what will be going with the AC signal.

So according to that a 1:10 transformer would present the cartridge with 470 ohms (47k / 10*10) and 1:15 would work out to roughly 209 ohms - but maybe I'm full of it that's just plain wrong an oversimplified.

[Barry]

As commented in the penultimate sentence in the last paragraph of http://www.kandkaudio.com/applications-guide/, the resistance of both the primary and secondary winding need to be taken into account when calculating the loading resistor.

[helma]

Thanks for the link, this is new info for me, have to check it out.

[Barry]

I should have added that the reason why you think the DC resistances of the transformer windings have little to do with the impedance transformation, is that for most MC SUTs these values are usually low. For some reason the Beyer designs have quite high values.

For example with a 1:10 SUT, the primary and secondary winding resistance values for various manufacturer's designs are as follows: -

Beyer: 85 Ohm, 4750 Ohm

Partridge D3061: 1.2 Ohm, 58 Ohm

Sowter 8055: 0.72 Ohm, 102 Ohm

Stevens and Billington TX-103: 16 Ohm, 102 Ohm

Haufe T-7883: 11.5 Ohm, 1300 Ohm.

[alcarmichael]

I should have added that the reason why you think the DC resistances of the transformer windings have little to do with the impedance transformation, is that for most MC SUTs these values are usually low. For some reason the Beyer designs have quite high values.

For example with a 1:10 SUT, the primary and secondary winding resistance values for various manufacturer's designs are as follows: -

Beyer: 85 Ohm, 4750 Ohm

Partridge D3061: 1.2 Ohm, 58 Ohm

Sowter 8055: 0.72 Ohm, 102 Ohm

Stevens and Billington TX-103: 16 Ohm, 102 Ohm

Haufe T-7883: 11.5 Ohm, 1300 Ohm.

With the above in mind and absolutely no calculations considered (I've had wine), the equivilant Sowter and S&B transformers at 15:1 would be more suitable for my requirements?

[Barry]

Sadly neither Sowter nor S&B have stock SUTs in their catalogue with a turns ratio of 1:15.

Furthermore I think the S&B TX-103 has now been replaced with the TX 1003 -10 (1:10 ratio) and the TX 1003-20 (1:20 ratio). Both of these designs use a much smaller magnetic core, which some claim to offer inferior performance

Again, I'm not sure if the Sowter 8055 is still available. Consultation of their catalogue only mentions one cartridge SUT: the 9570 with a ratio of 1:10. It might be worth approaching Sowter and asking for their advice.

[alcarmichael]

This lark isn't easy is it!?

Thank you very much for all your assistance 👍

[Barry]

You could alway try these: http://www.toroidal-transformer.com/shop/pro-audio/signal-transformers/378/tm3-step-up-transformer-1:15.html.

The technical information is a bit scant, but they are not too expensive, so worth considering.

[dmckean]

You could alway try these: http://www.toroidal-transformer.com/shop/pro-audio/signal-transformers/378/tm3-step-up-transformer-1:15.html.

The technical information is a bit scant, but they are not too expensive, so worth considering.

Those look like Haufe transformers.