Any Members Tried the Audio Interface CST-80 SUT?

My curiosity got the better of me and I just bought this SUT from Japan and wondered if anyone else had any experience with it. The very little I could find seemed to indicate it is a respectable unit and has even been likened to the highly acclaimed Cotter SUT.

It was made in the US around 1982 and came in two varieties. There was a 3 Ohm version with 30dB of gain and a 40 Ohm version with 20dB of gain.

I currently use a Fidelity Research FRT-4 which is excellent and has 4 different taps 100 Ohms, 30 Ohms, 10 Ohms and 3 Ohms + Pass Through for MM.  It will be interesting to see how it compares the FRT-4.

I will use it with my 1.0 mV / 60 Ohms Shinon Boron Red which currently uses the 100 Ohm tap on my FRT-4.


I’ve had the CST-80 for twenty years. I don’t know any specs on mine, they’re impossible to find. The website (which is very controversial and justly so) prefers it to the Cotter.

I already had the Cotter Verion SUT at the time I bought the AI, and was able to compare them in the identical system without relying on ‘audio memory’: it only took a second to switch back and forth. I also had a ‘Jury of Golden Ear Friends’ who helped me assess and choose whenever I got new components. Two were musicians, one a sound engineer, and we used recordings they performed on and knew intimately, or were present at the sessions.

I heard NO difference. But all three of them preferred the CST-80. One, a violist with the Berlin Philharmonic for over a decade, preferred it by a wide margin: he thought it captured instrumental timbre better, especially important to him.

I decided to part with the Cotter, but as I mentioned I heard no difference. My friends’ judgments swung it for me, plus the AI is only one-third the size, fits under my turntable, and is considerably more attractive. It also allows you to try different cables (eg copper vs silver, floating shield, etc) whereas the Cotter has captive leads of older design.

I’ve used it with many cartridges over the years. It has no loading options (neither did the Cotter) so you must look to your preamp for that. Sometimes I switch to a head amp (Thorens/EMT) but always return to the AI.

I look forward to your ‘review’ when you receive it, and how it compares to your FR.

bimasta, thanks for the great info. Can I ask which version you had, 3 Ohm or 40 Ohm and which selection of carts did you use.

Whilst I initially plan to use it on the Shinon Boron Red first, which seems to be a good match, I will ultimately want to use it with my Spectral Reference which may not be as ideal a match. The Spectral has a low output of 0.2mV and a very low impedance of 2 Ohm. 

I am hoping the low output and low impedance will not be too much of an issue with a quality unit like this. If it is an issue I can just revert back to the FRT-4.

Thanks again for the input.

All I know is the model — CST–80/II H. Maybe that tells you something, but H is a bit ambiguous. After reading your post about 3- and 40-ohm versions, I inserted my ohm-meter probes into the RCA females, but got no readings at all, so I can’t help there either.

I’m searching memory back 20 years as to cartridges I used. It included — Accuphase AC2, VDH MC10, Linn Asak, Coral (aka GAS Sleeping Beauty), Blue Oasis, Audio Technica OC-9, Madrigal Carnegie One, Dynavector 23 Ruby, Ortofon MC20 Super and MC30 Super, Audioquest 909, Fidelity Research MC 201 and FR1Mk3F — that’s all I can recall now.

All sounded lovely, within their own limits. A couple were irritatingly strident in the highs, and I blamed either the cartridge or the CST-80 — but they may have been innocent, I didn’t know much about loading then. It is the mythical “straight wire with gain”, though of course it’s wound wire. (Or possibly wound foil; such a shame so little info is available.)

I mentioned a Thorens/EMT head-amp last time. I like it a lot, it’s dead-silent and has better dynamics when I’m using a passive preamp. But I invariably move back to the CST when using active preamplification, either tube or SS — its transparency and purity is utterly beguiling.

Remember, I’m expecting your review...

Once again bimasta you have provided some excellent info. Thanks so much for the list of all those cart. 

I think your CST 80 H (high) is the 40 Ohm version like mine as I read elsewhere that the Low version is the 3 Ohm. It’s good to know that it appears very versatile. 

I won’t get mine for at least a week or two as they have not shipped it yet and it’s coming from Japan. But I’ll be sure to post my findings. 

I've always wondered why manufacturers of SUTs use a resistance/impedance measurement (ohms) as a way of communicating the specifications of their products.  (Not all of them do it, but too many do.)  It's not very informative for the un-initiated.
When it comes to transformers the two main factors to be designed around are the source and load impedances.  In the case of a SUT the source is a cartridge and the load is the phono stage.  This means that the cartridge impedance is the main factor that comes into play when mating it to a SUT. 

I agree Dave and it's one of the reasons I think the CST will not be ideal for my Spectral but it looks good for my Shinon.

As per my calculations if the CST has a turns ratio of 1:10 and my Shinon has an Output of 1.0mV and an internal impedance of 60 Ohms, then the output my MC Stage will see will be 8.87mV, but more importantly the SUT will give a reflected load of 470 Ohms or 7.8x the internal impedance of the cartridge.

The Spectral however, with its 0.2mV and 2 Ohms impedance will see 2mV at the MC Stage, which by itself is manageable, however the problem will be the reflected load of 470 Ohms which is 235x the internal impedance of the cartridge. Not ideal at all.

With the FRT-4 SUT I use the 3 Ohms tap which has a turns ratio of 35.8 and therefore the MC Stage sees 6.8mV and I get a reflective load of 36.6 Ohms or 18.3x the internal impedance of the cartridge.


+1 for the Cotter P transformer! I used it with the GAS Sleeping Beauty and FR 1mk3F. Nicely designed with Jensen transformers and a captive silver Verion Triaxial cable in a well-shielded blue case. Wish I had kept it! 
You matched it well roberjerman:)

The Cotter P Transformer was for very low impedance cartridges (2 to 30 Ohms) which would have been ideal for the FR1 MK3F which has a 10 Ohm internal impedance.
As an update for anyone interested I just discovered that I could reduce the reflective load from 470 Ohms to 40 Ohmn by installing a pair of 6600 Ohm Parallel Resistors.

The 40 Ohms would then be 20x the internal impedance of the Spectral cartridge and much more acceptable.
OK so the Audio Interface SUT arrived last night and first observation is that the unit is very small and very well made. A high quality product indeed.

Trouble is I’ve gone and put myself in a self inflicted dilemma which you will read about a the end of this very long post.

Firstly I love my existing Fidelity Research FRT-4 SUT. Not just because of the quality but also because of the versatility. It allows me to run up to three turntables, (I currently run only two), and switch between any cartridge I like with a simple turn of the knobs. It cannot be faulted in any way.

That all said I sat down last night with my copy of Melody Gardot "My One and Only Thrill" to do some A/B testing. The track I used was "Somewhere Over the Rainbow" as this has a variety of instruments, a beautiful vocal performance and lots of fine and subtle detail. I also know the track inside out and back to front.

I started with the FRT-4 and as usual it sounded excellent. I listened for many different things such as the tone and clarity in Melody’s voice, the timbre of the instruments, the sparkle in the higher frequencies, the extension of the bass with the lower frequencies etc. I also listened and observed the "air" around the instruments. For example how much space appeared between each instrument and the singer.

In this very critical analysis and without yet installing the Audio Interface SUT I picked up on a very very slight opaqueness to Melody’s voice that I thought could be improved upon. Apart from this minor observation I thought everything sounded sublime.

Switching to the Audio Interface and being totally cognizant of all of the small nuances of the track I just listened to, I observed the following.

The slight veil I had noticed over Melody’s voice was lifted and it became clearer. This slight improvement in clarity also extended to all of the other instruments and was apparent throughout the frequency spectrum and not just the higher frequencies.

Also the air around instruments grew a little and it felt that the subtle background instruments now had their own little place in the room instead of being slightly overpowered by the main instruments or singer. In other words the music appeared to come alive that little bit more.

From a tonal perspective, whilst there was a very slight increase in the resolution of higher frequencies it was in no way a "brighter" performance than the FRT-4. They both share a very similar tone and I think it simply comes down to the improvements in clarity.

I performed this A/B test on this particular track multiple times before switching to a couple of other tracks on the same album and in each case I think I can sum up that there is a slight improvement on the overall clarity and sound stage when using the Audio Interface SUT.

If a can use a very simple analogy it would be like when you are at the optometrist having your eyes tested and you think everything is totally in focus and then he switches to that last lens and your vision becomes that little bit clearer. That is what it seemed like last night.

However with that all said, there could be a possibility that the interconnect cable used had something to do with this improvement in clarity. For example the FRT-4 uses it own built in interconnect that is now some 30 years old, whereas the Audio Interface does not have a built in interconnect so I used my newer "Straightwire" interconnects. Not sure on that one, but it could be a contributing factor.

Now for the dilemma. I think I like the Audio Interface over the FRT-4 but it is early days and I need to do more comparisons at the weekend. It is also going to be a hassle when it comes to using my other TT or when switching cartridges as there will be no more simple turning of a knob. It will be a case of pulling out cables and ground wires and reinserting other cables and ground wires.

Also, as it is only a 1:10 SUT it will not work well with my much loved Spectral Reference without the use of some parallel resistors. In fact it is only compatible with my Shinon Boron Red as my other carts are either very LOMC or MM.

I think I will have to keep both for now and see how things go.

Sorry for the long post.

You promised a review, and delivered on that promise — a thoughtful and thorough analysis. May I ask what information appears on the CST’s case? Mine only says “CST-80 / II H” — and a serial number “40 1003”. Not much to go on. Maybe the spaced-off “40” in the S/N means 40ohms, which would mean 20dB gain.

But it handles my FR1Mk3F’s 0.14mV easily — in fact, with the volume on my preamp at only 8 o’clock, it’s blasting. Your 0.2mV Spectral should be fine — though its impedance is wickedly low.

Your dilemma is superior SQ (though not by much) vs Versatility. If you’re like me, I’d go with versatility... but always feel something’s missing, now that I know what’s ‘not there’. I’d always miss that extra ‘something’ and inevitably go back to the CST. But you have two great SUTs, and that’s not a bad dilemma to have. Our pursuit of the divine in music is fraught with dilemmas.

You can buy, or make, a switch-box to handle more turntables — but will that degrade SQ? A bit, probably — the FR’s switching capabilities may account for it’s slightly lesser clarity.

Even though its captive leads are old I’m sure they’re good (it’s FR after all; they used silver coils in their MCs at the time). I’m not sure replacing them with RCAs would help. At least the old leads are a direct signal path — yes, you could use “better” ICs, but chopping the signal up with additional solder-joints and plug connections might nullify any benefits a “better” cable could give you.

You’ve probably seen this review/lab-test of the CST when it was produced; it contains thorough data:

The site is also an archive of old reviews of serious equipment, fun to leaf through...

PS — No need to apologize for the long post — it wasn’t long enough! I'll be very keen to read your further ruminations and conclusions...

Hi bimasta, thanks for your kind words. Mine did not come with any box or literature but the sticker on the bottom states CST 80 40 Z which is the same as yours, 40 Ohms / 20 dB gain.

It’s funny that I too have the FR1 MK3F which is currently fitted to my other turntable so I will definitely give it a try this weekend and see how it sounds. For this cart I typically use the 3 Ohm tap on the FRT-4 which has 31 dB of gain and a 1:36 turns ratio.

I will also probably provide a further update once I put in some hours and do some more A/B comparisons with more diverse music genres.

Watch this space:)
I've learned quite bit through our conversation, Ateal, and thank you for that. I'll most certainly "Watch this space..."

Well it has now been a month since I received the Audio Interface SUT and I am still very impressed with the level of detail retrieval the SUT provides.

Whilst the FRT4 SUT is an excellent performer and is super versatile, the Audio Interface SUT has taken my music to the next level.

Things that have stood out in the past month have been the "unmerging" of certain musical combinations. For example where there are passages of music that have a number of instruments playing in close proximity to each other, the Audio Interface appears to pull them a little further apart so they each have a little more separation and because of this, each become clearer and more distinct.

Also vocals have become a little clearer. For example I have listened to the Vanessa Fernandez song “Be Thankful for What You Got”, hundreds of times and never really focused or over analyzed the exact lyrics. Because of this I always subconsciously thought one of the lines was saying “TV enters in the back”. When I played this track the other week I was in my usual relaxed state and not over analyzing anything about the track, but this time to my surprise I heard something different and that was “TV antenna in the back”.

I know this is embarrassing to admit and I obviously hear it now with both SUT’s and even in the You Tube video, but it was the Audio Interface that made it so obvious.

The one other thing that it does a little better is revealing very subtle details that are not as noticeable with the FRT4. Subtleties like the breath of a saxophonist in between notes, the very tiny triangle note in a complex musical arrangement, the distant cough from the audience in a live performance, etc, etc.

I think if you are a fan of classical music then this SUT would be very hard to beat as it would pull apart very complex music arrangements and subtle details that are so common with this genre and provide a very dynamic performance.

The only down side is, that with some harsher recordings you may want a slightly more mellow and veiled presentation as too much detail retrieval and transparency can be slightly fatiguing. I have only noticed this with a couple of records and for 99% of the time it is not a problem.

In summing up I have now come to the realization that the initial amplification of a Moving Coil cartridge is one of the most important aspects of vinyl playback and should be given as much attention and investment as the cartridge itself. Whether you choose passive or active pre-amplification I believe you must spend as much as you possibly can to make sure the signal from your very expensive cartridge is not degraded in any way whilst on its way to the phono input of your main amplifier.

I am so impressed with the Audio Interface CST 80 SUT “H” that I have managed to find and purchase for a very reasonable cost, the very rare 3 Ohm “L” version for use with my very low output moving coil cartridges.

In summary I wholeheartedly recommend this SUT to anyone looking for a high end MC phono stage.

That’s if you can find one :)

As I was searching for more info on this SUT today I came across this review from Audio Asylum in 2006. It pretty much sums up my own findings.

This is the mc trans believed to contain jensen trans', and actually may have been bought by the Jensen company. I got it used from Audio Directions in Honolulu for a very good price, with a very long trial period...the owner is that way. He deals alot with CJs, VTLs, and Quicksilver amps. He also deals with Hagerman, who is also based in Hawaii. If ever in Hawaii, check it out. He has stuff piled up all over the place. I am in no way affiliated with Audio Directions. Just a happy customer of a few years.
I introduced the cst first to my technics sl1500mk/denon 103/project tube box/leben cs300/fostex 126e system, and to put it shortly, all the good stuff came shining through...more background details, more sense of air and space, authority from top to bottom. base got deeper and punchier (yes, even thru the single drivers). just alot more ease and drive to the music. All the good stuff we love about music through vinyl, but MORE!
But, I didnt have too long to assess the AI in my technics system because I immediately set up my newly arrived Garrard 401 with the rega rb300/expressimo weight with cardas wire upgrade.
Getting the Garrard set up needs another post entirely, but lets just say for now it was like waking up an old needs tlc, a couple of slaps, a few drinks, a massage, and it needed to run upside down for a little while...I aint kidding. OK. Now the AI is extracting what the 401 can do. With the 401, Sam Cooke stepped into my living room. His tonal inflections are living and breathing, the band filling my whole room. With the Garrard, the best word I can sum it all up on is "visceral".
What does this mean? i guess it means the Audio Interface gives you more of what you have...brings out the latent image, sort of improves your "hearing".This is my first experience with mc trans', so take it for what its worth. I am just excited with all my new additions, so maybe its hard for me too make a clear assessment, but it sure is FUN, and isnt that its all about anyway?

@ateal , My first SUT was   FRT4. Because this one is

copper version I wanted to check the output cable. I was

surprised about the amount of corrosion. So the obvious solution

is to solder an new cable. I moved then to Denon-AU-S1 which is

better made and without all those aluminum switches in the

signal path. I hope you also changed the output cable?

Hi nandric, I opened my FRT 4 when I first got it and it was clean as a whistle, no corrosion, like new. 

I should clarify that the FRT 4 is outstanding but the AI just gives that little bit more.
Coming in late here, but, a friend gave me one of the 3 ohm versions to sell for him along with several other pieces. I don't need it for my own system as I added Sowter SUTs into my Hagerman Trumpet years ago. I'm trying to get a sense of the value of this. Thoughts?
I saw one not long ago on a Japanese site for $999. But it may be gone — which would suggest it's a viable price. On the other hand I paid $60 for mine. Somewhere in between seems right. Does that help?

OTOH, I've seen Cotters selling fast in the $2–3+K range, and many consider the AI better... but as we know perceived value and true quality are not related.
Dear @piedpiper :  Early this year one gone for 400.00. So between 500.00/ 600.00 price to negociate with  could be ok.

Having purchased both versions recently I think $400 would get you a very quick sale for the 3 Ohm version as this price is an absolute bargain for what it is. 

I think $700 is probably the high side but you could still get a buyer if someone knows enough about this SUT and really wants one. I personally think $700 is fair value for this SUT as it is truly outstanding. 
I notice there is one for sale in Japan for $900 but it has obviously gone unsold for quite some time. That kind of brackets the price effectively. I wish I had a use for it but I look forward to finding an appropriate home soon. Thanks again!
Is there any chance you could compare against your Hagerman and report your findings. Sure would be good to see how this little SUT compares to one of the great Phono stages. 
I have to add that after six months with the 3 Ohm version of the Audio Interface I am still blown away each evening with the way this SUT manages to create the most amazing holographic soundscape. 

I am currently using it with a rotation of Fidelity Research PMC1, MC202 and Spectral Reference. All LOMC’s around the 0.2mV range. 

My journey with SUT’s has been like a restoration project on a rare and historical piece of art. With each SUT it has been like removing a single layer of grime from the artwork and then in comes the Audio Interface like a super cleaner that makes that 15th century piece of art become super crystal clear with every nuance and color contrast being visible for all to see. 

Suffice to say, the FRT4, whilst very very good, has gone to a new home. I will keep both 40 Ohm and 3 Ohm versions of this amazing SUT. 
Hello to all that posted in this thread about the Audio Interface CST-80 passive transformer SUT's. I just joined your forum so I could provide the history of the CST-80 to you members, including "bimasta" who said that specs on the CST-80's are impossible to find.  

My name is Dave Hill, Gen. Manager of Jensen Transformers, Inc. in Chatsworth, CA. Since 1974, Jensen Transformers has been designing and manufacturing the highest quality audio transformers available worldwide.  Our founder Deane Jensen was a brilliantly gifted, analog audio design engineer who knew how to design audio transformers that would perform as open, natural and uncolored as possible. Deane's line of transformers finally solved the classic complaints about the high frequency harshness and a mid-range "smear" that poorly designed transformers, made with low grade materials, would add to a piece of audio gear.

I have been with Jensen Transformers since June of 1980, so I was here when Deane Jensen created the two Jensen moving coil cartridge transformer models, the JT-34K-DX and the JT-44K-DX, that were used in the Audio Interface SUT's. Deane developed them with the help of a local hi-end audio person, Anthony (Fujio) Suganuma, who owned an accessories company called Audio Interface located in Van Nuys, CA. "Numa-san" helped Deane by performing critical listening tests of the original prototypes. This led to the creation of the Jensen JT-34K-DX and JT-44K-DX m/c transformers. In return, Audio Interface was given exclusive rights to be the first company to produce a high quality, Jensen transformer based, passive moving coil cartridge step up device. As you know, there were two versions of the CST-80 that contained either the JT-34K-DX high ratio/high gain (31 dB) transformer, or the JT-44K-DX low ratio/lower gain (20 dB)  transformer.

Now for the good news: We have in our archives copies of Audio Interface's data sheets for the original CST-80 model, and the later CST-80/II version. The data sheets do not say that there are Jensen m/c transformers inside, but we also have a copy of an advertisement from "Audio Magazine" that says the transformers inside were exclusively made for Audio Interface. I can send an electronic copy of the ad, and the two data sheets upon request sent to:

Now for even better news: our ISO-MAX model MC-2RR passive SUT is a faithful recreation of the Audio Interface CST-80, using the same model Jensen transformers and internal circuitry. We make two versions: the MC-2RR-L 1:10 ratio model for 20 dB of gain, and the MC-2RR-H 1:37 ratio model for 31 dB of gain. They are available now directly from us. 

One final note: the CST-80's were filled with black epoxy to disguise the Jensen models inside. This also prevented the end user from trying different Zobel networks, or adding an additional resistor across the input RCA's to change the cartridge loading. Our MC-2RR's are not potted, which allow you the flexibility to experiment with loading and Zobel networks.

For more information, contact Dave Hill at:  
Hi Dave, this is fantastic information and very informative for me personally as I own both the high and low output versions of this incredible step up transformer. 

It is also great that you are recreating this well regarded SUT in modern form so that many others can easily try it out for themselves. 

If they are anything like the originals they will be very special indeed. I have no intention of selling my Audio Interface SUT’s anytime soon as they seem to impress me more and more each day. 

I will definitely take you up on the offer of the advert and data sheets as they will be great to have. I will email you shortly. 

Thanks again for posting the history of this SUT and the offer to supply the data sheets. 

Your SUT is less expensive than the AIs available on ebay.   My friend is anxiously looking for an AI but at under $500 for the L (low output version).  Thanks so much.

P.S. Do you have an opinion concerning the Zesto 10 impedance/4 output level Andros Allasso SUT?  Can it possibly be as good sounding as your Jensen?  Thanks (I need some adjustment for various cartridges but don't want to sacrifice sound quality).  
Adding to this old thread......
I've owned the CST-80 since 1988... got it used for I think $160.  It's the only SUT I've ever owned and always wondered where it ranked in overall quality of SUTs.  Based on what i'm reading here, it's in the 500-1000 category of new SUT's.  
I'm using an Ortofon MC-30 Super-II... and I've often switched between using the MC gain stage of the phono pre and using the SUT.  I do get more raw detail and LF extension without the SUT, but WITH the CST-80, the noise floor is lower, and there is a mid bass fullness that makes the music bloom more.  It simply sounds more punchy & musical..... at the slight expense of HF transparency.   Overall, I find myself preferring the sound using the SUT.   My current phono pre is the Parasound JC3.

Someday I'd like to hear an SUT in my system based on Cinemag or Lundahl transformers, just to see where my CST stands.
Jensen is currently producing a version of the CST-80 for $550, and Hafler's current SUT for $999 uses the same Jensen transformers!   I'd say the new Jensen is a safe buy, as I've been happy with mine for over 30 years.