Ortofon ST-70 Moving Coil Transformer Review

[morillon]

Ortofon destines this SUT for their Cadenza series as they say.
Here's the specs of one of them:

View attachment 462172

MC Cadenza Red

Cadenza, derived from the Italian word "cadence," designates a segment within a musical performance, typically a concert, where the orchestra ceases its play, allowing the soloist to perform independently, unrestrained by a strict rhythmic pattern.This solo passage, known to as a cadenza...

ortofon.com

...and here's the top of the line:

View attachment 462173

MC Cadenza Black

Cadenza (from Italian: meaning cadence) refers to a portion of a concert in which the orchestra stops playing, leaving the soloist to play alone in free time, without a strict, regular pulse. A cadenza can be written or improvised. It’s usually the most elaborate and virtuosic part the solo...

ortofon.com

The 5 Ohm config seems to be the right one.

At Ortofon, we can consider actual cartridges up to 7 ohms... B setting...

Ortofon has always been culturally focused on low-impedance cartridges...
This seemed to be the setting used during these tests... the B... less of 10ohm...
not 22...of AP

that's all...
;-)

 

[Sokel]

At Ortofon, we can consider actual cartridges up to 7 ohms... B setting...

Ortofon has always been culturally focused on low-impedance cartridges...
This seemed to be the setting used during these tests... the B... less of 10ohm...
not 22...of AP

that's all...
;-)

I think the mystery is solved by AP themselves, I quote:

Measuring high impedance sources, such as some high impedance audio transformers, can result in poorer high-frequency performance than expected. This is due to an input shunt capacitance of around 190–300 pF that is present in almost all audio analyzers. AP’s APx500 Series has a shunt capacitance of 220–230pF, while the 2700 Series has a shunt capacitance of 95 pF in balanced mode (differential) and 185 pF in unbalanced mode.

Here's the article:

Measuring High Impedance Sources

Learn how to measure high impedance sources and overcome challenges caused by input shunt capacitance in audio analyzers, and which approach not to take.

www.ap.com

 

[Hayabusa]

I think the mystery is solved by AP themselves, I quote:



Here's the article:

Measuring High Impedance Sources

Learn how to measure high impedance sources and overcome challenges caused by input shunt capacitance in audio analyzers, and which approach not to take.

www.ap.com

And the fact that the input is driven by 20ohm in stead of 5, which most likely explains the lower frequency deviation.

 

[Balle Clorin]

Found son old stuff I repost here for completeness.
While I was learning how to measure SUTs I got some strange result on the way, two different methods here. Improper actual loading ,

Doing it with sound cart with too high input capacitance…and just looking at the Difference, but you still see the effect of different source resistance.. the bottom one is just inserting the SUT in test loop with no precautions..very misleading results

And finally varying source resistance and using an actual RIAA as load( Parks Audio Puffin 47k, flat EQ,Toslink out, limits bandwidth to 48k max) .
This is the “True” respons a a user can get with different cartridge resistance. Sony HA T10=Ortofon T5

 

[DSJR]

This reminds me of my ongoing question about Audio Technica tip profiles. They consistently charge a premium for Shibata and Special Line Contact profiles over Micro Line. Is it just marketing to uninformed audiophiles? Or is there a compromise with ML that Audio Technica think better serves the audience with the more expensive alternatives?

What follows is a subjective vibe, so please take or leave as you see fit

Someone somewhere posted a vid of the three main AT OC9 (low output MC) stylus profiles playing the same record. I can't remember the music, but to start with, may I suggest that a given cymbal can vary its tone if struck or brushed in different ways (jazz drummer Alan Ganley was a master at this I remember).

The OC9 with 'naked' elliptical tip sounded fine in isolation, but switching to the ML tip, gave a bit more sparkle and perceived 'definition' up top and the classic 'OC9' tones as I remember them over the decades (lean, clean and maybe slightly 'snappy' in some setups). The 95ML does this too and can beneficially 'spice up' many a flagging vinyl system. The OC9 with Shibata tip kept the perceived 'detail' of the ML, but refined it into something I hear live if percussion is played by a master, the differing 'timbres' of cymbals being better defined over the slightly 'one note' ML perception in comparison.

The above of course, assumes the arm was set the same, but my experience of the later Shibata tipped pickups does seem to indicate a worthwhile sense of hf refinement. I've not heard the VM95SH to see if the cruder cartridge internals justify this diamond (the ML does seem the best value), but the better-body 700 models may be good here. I'm just a bit disturbed by the claim of 'extra warmth and realism' from the VMx range, as the last thing you want from mid-range pickups is more 'warmth' FFS

To answer your comment, the ML stylus is used a lot by AT, so maybe there's a cost benefit in the quantity they make? I was told decades ago that the ex-works costs of different tip/cantilever assemblies isn't that vast per unit, so maybe marketing and perhaps more critical and careful alignment of the complete stylus assembly adds to costs (one maker suggested that in the case of exalted MC types, the fancy box and packaging often costs more than the cartridge itself ex-factory and only the gemstone bodies really began to justify the high prices...

 

[SIY]

I suppose, if there is an alternative product that is really insensitive to loading, it would be a much superior product. And there is, right?

You can go electronic, but getting the noise to the equivalent of a transformer without excessive bias current is not cheap. And, of course, transformers make balanced input operation easier (though curiously this was not implemented by Ortofon). Someone earlier mentioned the Vendetta, which has worse noise than a transformer hooked to a more conventional gain stage and at a premium price. The Michael Fiedler (sp?) units look quite nice, but are still higher noise than a transformer stage.

One could argue that we swiftly hit the limitations of other noise sources (vinyl surfaces, cartridge Johnson noise) and that's the best argument one can make. But still, good transformers run with balanced inputs have fabulously good common-mode noise rejection and, fashion things like the Ortofon aside, can be very reasonably priced- the Sowters I used in my MC preamp cost about $200 for the pair and gave superb performance.

 

[markstein]

I am using my RME Fireface UFX II mic preamp with balanced connection to the AT 33PTG/II and definitely do not have any noise issue with 60dB gain. This setup is dead quiet. RIAA equalization is done using Acourate convolver on my PC. Input level can be optimized - any clipping is indicated by the Fireface.

Now, if I compare the price of my setup (which is already expensive) vs. this Ortofon SUT, I do not see the use case for such a product...

 

[Cbdb2]

I suppose, if there is an alternative product that is really insensitive to loading, it would be a much superior product. And there is, right?

Yes, you put an amp (opamp circuit) after the transformer with the proper input impedance to load the transformer. But you still need to know the transformer input loading or add an input amp and it becomes an active device that needs a power supply. And as Siy has said this will probably increase noise.

 

[Balle Clorin]

You missed the irony here I think,.. a RIAA for 300-500 usd will have a decent enough MC stage to make any SUT unnecessary. Come to think about it my whole vinyl system is unnecessary …

 

[mike70]

Those results are not necessarily awful, as they are likely to be a direct result of how they were measured. As has been repeatedly mentioned above, a transformer needs very specific source and load impedances to provide a flat frequency response, but the lack of such detail in the specification means that the measurements will most likely be very different to each use-case. Given that the transformers used are from a very reputable source, I expect the results would be pretty good had the optimised source and load been used in the measurements.

The difficulty with such a product is that hardly any user would be in a position to know or be able to optimise use conditions so would get results very different to what could be achieved, and also likely to be very different to the measurements reported here.

S

well, that's what i suspect, if you read my post carefully ... my SUT is much cheaper and doesn't destroy the signal ... it's strange that a 1500 USD SUT goes that bad.

 

[Nango]

Tear down, tear down!!!

 

[LTig]

You can go electronic, but getting the noise to the equivalent of a transformer without excessive bias current is not cheap. And, of course, transformers make balanced input operation easier (though curiously this was not implemented by Ortofon). Someone earlier mentioned the Vendetta, which has worse noise than a transformer hooked to a more conventional gain stage and at a premium price. The Michael Fiedler (sp?) units look quite nice, but are still higher noise than a transformer stage.

One could argue that we swiftly hit the limitations of other noise sources (vinyl surfaces, cartridge Johnson noise) and that's the best argument one can make.

This! With both my retired DIY phono stage (AD797) and the Cambridge Audio Duo fed by an AT33PTG/II (0.4 mV spec) the noise floor is much lower than the best vinyl I own. Even when I hear loud, after lifting the needle it's dead quiet. No SUT for me, hence.

 

[Balle Clorin]

well, that's what i suspect, if you read my post carefully ... my SUT is much cheaper and doesn't destroy the signal ... it's strange that a 1500 USD SUT goes that bad.

How do you know? .
Take a look at my posts here , you may get an indication of what goes on both in this review and with your own.
Giving a SUT an unsuitable source resistance and offspec load can do strange things.. I suspect this is the case here too.

What is unsuitable can be surprising .. a SUT operating optimally with 3-40 ohm or 5-50 does not exist. One set for 3-5 ohm will not be good at 20 ohm source resistance. SUT makers are not truthful about this in fear of loosing sales.,

 

[DVinylfan]

Following this thread with interest...has anyone tried placing a pyramid-shaped sticker on this thing?

 

[Cbdb2]

For those who want to dig deeper, the audio transformer bible. Bill Witlock Including how to test transformers. Learned something new there, testing small transformers, like these, with a regular ohm meter for DC resistance can magnetize the core.

https://www.jensen-transformers.com/wp-content/uploads/2014/08/Audio-Transformers-Chapter.pdf

 

[somebodyelse]

Tear down, tear down!!!

Was post #27 not good enough? There really isn't much to see.

 

[Balle Clorin]

Hello, The exam you performed seems to correspond to configuration B, which is the default for input impedances < 10 ohms. The measured gain goes in this direction. The user manual is available on the ortofon website. For the AP, configuration A seems more appropriate. To change the configuration, you have to open the device and change the position of jumpers. This may be the reason why the frequency response is so poor.

https://ortofon.com/cdn/shop/files/ortofon-st-70-userguide_web.pdf?v=2387460436607555332

In any case, the device is quite expensive for what it offers.

Exactly! This explains a lot, But who knows how config A would look like, 5-50 seems like a too large range to be optimal in any way, but maybe 20ohm could have been the sweep spot. Sadly this test was a missed opportunity .My guess is that this unit is tailored to be used with a 5 ohm Candenza and config B, <10 ohm 30db, And that config A 5-50 ohm 24db is just utilizing the second wiring option of the Lundahl and hoping for a listenable result,
.

 

[morillon]

Exactly! This explains a lot, But who knows how config A would look like, 5-50 seems like a too large range to be optimal in any way, but maybe 20ohm could have been the sweep spot. Sadly this test was a missed opportunity .My guess is that this unit is tailored to be used with a 5 ohm Candenza and config B, <10 ohm 30db, And that config A 5-50 ohm 24db is just utilizing the second wiring option of the Lundahl and hoping for a listenable result,
.

If I often point out my surprise that I have not tested the two minidsp ADCs...

it is clear that concerning the Adept (the pocket is just an small ADC) and its phono part, the AP is not the most comfortable source for this use which in principle justifies more dedicated sources for technical rigor (claimed)
;-)

 

[sergeauckland]

How do you know? .
Take a look at my posts here , you may get an indication of what goes on both in this review and with your own.
Giving a SUT an unsuitable source resistance and offspec load can do strange things.. I suspect this is the case here too.

What is unsuitable can be surprising .. a SUT operating optimally with 3-40 ohm or 5-50 does not exist. One set for 3-5 ohm will not be good at 20 ohm source resistance. SUT makers are not truthful about this in fear of loosing sales.,

I also suspect they don't make that information obvious, as so few potential purchasers would understand what they're being told, or would have any means of ensuring the correct loading. I think transformers have many valuable properties, which is why I like to use them, but they are not 'universal' in the way that an electronic Step-up can be.

Microphone transformers are very similar to MC cartridge transformers, but they are normally installed in a mixing desk, where the loading is known and fixed, and present a reasonably standard impedance to the microphones. MC SUTs are sold to consumers, not having any control over the conditions of use.

S.

 

[Newman]

You can go electronic, but getting the noise to the equivalent of a transformer without excessive bias current is not cheap. And, of course, transformers make balanced input operation easier (though curiously this was not implemented by Ortofon). Someone earlier mentioned the Vendetta, which has worse noise than a transformer hooked to a more conventional gain stage and at a premium price. The Michael Fiedler (sp?) units look quite nice, but are still higher noise than a transformer stage.

One could argue that we swiftly hit the limitations of other noise sources (vinyl surfaces, cartridge Johnson noise) and that's the best argument one can make. But still, good transformers run with balanced inputs have fabulously good common-mode noise rejection and, fashion things like the Ortofon aside, can be very reasonably priced- the Sowters I used in my MC preamp cost about $200 for the pair and gave superb performance.

Thanks, but my comment was really about the criticality of loading of the SUT being a significant issue with a big effect on FR, and all being unnecessary since there is an alternative that completely solves it and creates spot-on FR.

Whereas the noise from a decent non-exotic MC preamp seems to be a real problem only in the minds of theoreticians. I just don't hear people using a good MC pre and saying "gee the noise intrusion is a big issue". (Maybe with bad ones...)

So it becomes a real problem, easily fixed, vs a theoretical problem, made a mountain of.

cheers