graham67

SUT experiences

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Thought I would share some thoughts on my experiences with SUTs. 
 
Despite having had phono stages that support both MM and MC, I have ended up preferring the sound of my MC carts via SUT into the MM setting.  I usually find that a well matched SUT brings an extra level of refinement and removal of grain compared to using the MC settings.  They also reduce the background noise compared to using active gain.
 
However it can sometimes prove a difficult exercise finding a good match between SUT and cart.  I have found that a badly matched SUT can destroy the dynamics of an MC cart.  It also doesn't help that I find the theory and calculations somewhat bewildering, so usually default to manufacturer recommendations where available.  Also hard bitten experience and word of mouth recommendations are most valuable.  A fellow wammer once suggested the absurdly cheap HFN Black Head SUT for the AT OC-9 as this was a combo he found worked well many years ago.  And after a quick trawl and low cost purchase on ebay, so it proved, the Black Head bringing a creamy but expressive smoothness to the top end of the OC-9 ML2. 
 
But in the main, my best results have come from using a SUT designed for the cart.  For example, the Auditorium A23 brought the best out of a Denon 103.  Similarly I have also found that the inexpensive Audio Technica 630/650 from the 1980s work well with the AT33PTG2, a cart not dissimilar to the AT32E and AT33E that were the natural partners of these two SUTs when new.  I once owned a nice Shelter cart which I was never able to get good results from.  Only once I heard it with a high quality multi-adjustable S&B SUT did I realise how good a cart it was.  However I also had to accept that I would not be able to afford the required SUT so I ended up selling the cart.
 
But despite the potential pitfalls, I have never had to spend a lot to get a good result as there are some good used bargains to be had.  And of course being an entirely passive device SUTs dont break down so present a low risk used purchase, that can always be sold on at little or no loss.
 
So if you are tempted, I would say give it a go. But do your research first on the specifications needed for your cart, or alternatively (like me) just seek help from a more knowledgable wammer!

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Good advice,would also recommend to try before you buy or hold,or attend some bake-off's.I tried numerous SUT's in my system before deciding on what worked for me.

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11 minutes ago, GJO said:

Good advice,would also recommend to try before you buy or hold,or attend some bake-off's.I tried numerous SUT's in my system before deciding on what worked for me.

:^

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Cartridge loading, in fact any form of interstage loading is often misunderstood. I use the analogy of a swinging door, if the power of the push is low then the resistance of the door and what is beyond it makes the process hard and the music suffers if they are not matched to help the process. This is especially the case with SUTs as all a transformer can do is convert available current to voltage gain, and there is damn all current coming out of a phono cartridge and therefor out of the SUT, so it is bordering on the what is possible. SUTs were only used by the likes of Ortofon with early SPUs because the technology of amplification was too noisy to work at those low voltage levels with valves or early germanium transistors. With the development of low noise transistors and op amps the problem has gone away, but still some people seem to prefer the sound of a circuit struggling as in valves with SUTs, that is fine and their choice, and of course to perform it has to be carefully matched in loading to help it. Now with a low noise solid state phono stage with a high current linear power supply the problem just goes away, as the available current and voltage headroom is massive. So the door (to use my analogy again) is just bashed open no matter what (within reason) the matching loading is. All you get in this case and only with poorly designed stages is a slight change in frequency curve. With stages designed with massive headroom you need no messing around with loading it can be left at 47kohm for MM (and high output MC) and 470ohm 470pf for low output MC, and the only cart that requires special loading that I have found is the AudioNote IO (the version with field coils).

Not meant to deny other peoples experience but often quotes on SUTs and loading are made without fully understanding what is going on.

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I agree with this. Electronic step ups have many advantages, not least that of easily adjustable loading, making it much easier to find a good match for the cartridge. 

Transformers can give slightly lower noise than active devices, but the difference today with modern transistors is very small, and in any event is still way below the inherent noise off an LP. 

If one has a choice of SS or transformer Step up, I'd go for SS every time. Maybe the IO is the exception.

S

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The problem is if the interfaces are susceptible to different loadings then it is very much suck and see to get it right, there are no real hard and fast rules to decide. IMO the more components / switch contacts etc in the signal path the more the music is corrupted. In current fave SS phono stages there seems to be a very different approach which is to get this process as complicated and confused as possible with DIP switches and multiple loading options. Also so many phono stages now seem to rely on the PSU in the plug you put in the wall - IMO daft. I understand why, it make production simpler (less need for regulations compliance), a way around the rules, but nothing beats VA and lots of it.

Edited by nva

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2 hours ago, nva said:

...but still some people seem to prefer the sound of a circuit struggling as in valves with SUTs....

Not meant to deny other peoples experience

It certainly does seem popular these days for MC users to prefer SUT/MM over MC stages but in my experience there is a degree of 'romance' involved with the transformer and/or valve approach and I don't feel this solution is really representing the true sound of the cartridge. Similarly I don't mean to deny others experiences and at the end of the day, if it sounds good to the user they have achieved their goal.

However, personally having tried a million and one combinations of SUTs, head amps and phono stages, in terms of accuracy I prefer a modern low noise MC stage.

That said, I also like dip switches as it's a convenient way to switch from MC to MM :ph34r:

 

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Somebody should design some hifi were it can be upgraded by using better power supplies. Top business idea that is.

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If it were that simple. A power supply is not or should not be an entity, it should be a part of a whole. It can be in a separate box, and with phono stages (especially for MC) as the VA goes up that is essential due to hum fields created by larger transformers, but it should be looked on as part of the design, not as an after thought. In many ways with audio circuits power supply design is the most important part.

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3 hours ago, nva said:

the only cart that requires special loading that I have found is the AudioNote IO (the version with field coils).

Why is that version different from the other IOs?

They all have a similar output.

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The version with field coils and external power feed, has far lower output. Years ago Coco San brought his one around to my house fitted in a SP10 (I forget the arm). I hated the SP10, grey sounding, but could definitely hear how good the cartridge was, just very noisy. I felt my fitted standard 470ohm 470pf was not exactly right and you had to really feed in the gain. This is obviously a unique cart and there are so few in use it would be worth making a special effort to get it right. This amoungst literally hundreds of different carts used with that phono stage was the exception that proved the rule.

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17 hours ago, graham67 said:
I usually find that a well matched SUT brings an extra level of refinement and removal of grain compared to using the MC settings.  They also reduce the background noise compared to using active gain.
 
However it can sometimes prove a difficult exercise finding a good match between SUT and cart.  I have found that a badly matched SUT can destroy the dynamics of an MC cart.
But in the main, my best results have come from using a SUT designed for the cart.  For example, the Auditorium A23 brought the best out of a Denon 103. 

Yes, I find that a good transformer can sound superb.
I think the idea of "matching the impedance" has been blown out of all proportion and led to a lot of confusion.  "Matching" the impedance - ie having the load seen by the cartridge equal to its internal impedance - will give the absolute maximum voltage step-up, but that isn't really the goal when using  a step-up transformer.  What we're really aiming for is the correct signal voltage for the mm phonostage.  In the vast majority of cases a transformer turns ratio somewhere between 1:10 and 1:20 will do the trick, though there are (a few) exceptions.
Unfortunately the turns ratio is something that most transformer makers stay mysteriously quiet about.  Why?  It's the most important thing.  BTW, the Auditorium 23 doesn't specify a turns ratio and I can't find a mention as to why it is particularly suited to the Denon 103, but if you found it to work well with that cartridge that's all that matters.

6 hours ago, nva said:

...all a transformer can do is convert available current to voltage gain, and there is damn all current coming out of a phono cartridge and therefor out of the SUT, so it is bordering on the what is possible.

It's true that the signal voltage from a LOMC is very low, but its source impedance is also very low - that equates to a high current capability.  A 1:10 turns ratio and a 47k MM phonostage presents the cartridge with a 470 ohm load, and that's an easy load for a cartridge with a source impedance of ~10 ohms (which is not unusual).

4 hours ago, nva said:

.. so many phono stages now seem to rely on the PSU in the plug you put in the wall - IMO daft. I understand why, it make production simpler (less need for regulations compliance), a way around the rules, but nothing beats VA and lots of it.

I don't think there should be any need for a large VA power supply for a phonostage, and I don't see a problem with using a plug-in-the-wall type as a starting point - it should be perfectly possible to filter and regulate it to produce a very clean voltage for the phonostage to work with.

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41 minutes ago, Rothwell Audio said:

I don't think there should be any need for a large VA power supply for a phonostage, and I don't see a problem with using a plug-in-the-wall type as a starting point - it should be perfectly possible to filter and regulate it to produce a very clean voltage for the phonostage to work with.

Well I can empirically prove my point and have done on hundreds of occasions with people comparing the same circuit phono stage with 30va to 120va to 240va to 1200va linear power supplies with a clearly heard progression between them, and I could link you to where people have talked about it. What a circuit *needs* is not what it wants to perform to its ultimate.

Anyway it is not my job to teach electronics and I can prove anything I say and hopefully will be able to here in the near future.

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51 minutes ago, Rothwell Audio said:

It's true that the signal voltage from a LOMC is very low, but its source impedance is also very low - that equates to a high current capability.  A 1:10 turns ratio and a 47k MM phonostage presents the cartridge with a 470 ohm load, and that's an easy load for a cartridge with a source impedance of ~10 ohms (which is not unusual).

Well I suppose it depends on what you call high. As a kid I remember as part of my "Wireless World" fun wiring up the crystal cart on my record player to a small bulb and watched it pulse with the music - first light show xD a Moving Magnet would have a chance off creating a flicker, a Moving Coil would be nothing, same with the output of a SUT as the impedance of the light bulb would pull the amplified signal down to virtually nothing as there is so little current available. With a SUT you are working just within the bounds of possibility which is why spending so much money on them with silver wire and massive iron cores brings appreciable benefit, by removing as much inherent loss as possible.

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One reason why your hear (measure?) differences with different sizes of mains transformers is that you will get

a different power rail waveform with its attendant harmonics. Depending on the power rail regulation and the

susceptability of the circuit to power rail disturbances you can often get different sonic results. A different type of

trnasformer can also affect such things as mains borne noise etc.

Purely as an example In the past a popular pre amp/MC phono stage was susceptable to different power supplies. The circuitry

had relatively poor PSRR and was affected by different power supplies which were primarily different sizes of mains toroids. A common

third party modification was to power the pre-amp (inc the phono stage) from a more sophisticated power supply. One that comes to mind 

was built using low VA EI frame transformers (100VA) and well sized R/C filtering while the original used a large 500VA toroid and a single

large capacitor. The regulation was the same being LM317 based.The power rail spectrum on the replacement supply was far cleaner than

the original which was reflected in the sonic results.

Changing the size of the mains transformer made little difference to the power rail spectrum until a point was reached where the transformer

was clearly beginning to get too small. Conversely when it was made larger both mechanical and radiated noise became an issue so 100V was

chosen as the optimum in this case.

Im using this example to show that in my experience the actual size of the mains transformer is not the sole arbiter of performance.

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