Any Members Tried the Audio Interface CST-80 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.