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 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.