SUT - electrical theory and practical experience
Some vinyl users use a SUT to enhance the signal of the MC cartridge so that it can be used in the MM input of a phono stage. Although I don't understand the theory behind it, I realize that a SUT should be matched individually to a particular cartridge, depending on the internal impedance of the MC, among other things.
Assuming an appropriately / ideally matched SUT and MC, What are the inherent advantages or disadvantages of inserting a SUT after the MC in the audio chain? Does the SUT theoretically enhance or degrade the sound quality? What does the SUT actually do to the sound quality?
Thanks.
@intactaudio Your last response is what I would call an IP reveal and very generous as an offered information. I carry info' like this from my Bespoke Designs I own,but have always felt my liberty was best constrained when the opportunity arose for sharing the Designer/Builders IP. I once had an awkward conversation with a not very well known to me EE at an event where I was demonstrating a device, they were keen for me to allow them to remove a Chassis bottom plate and let them see inside. I was adamant that that would be quite a betrayal to the designer with whom I have developed a close to 30-year friendship. |
Some observations: I always found the specs for a cartridge confusing: 0.25mV output at 5 cm/second. Into which load? Open circuit? Load=Cart impedance? Load=recommended impedance? Why not state the output voltage and the impedance at which it is measured? Most recommended load impedances are specified over a large range (100Ω-1K), and they are all usually 10x the cart source impedance so the voltage divider effect will be small, but in some cases, it could have a significant impact on the output.
Matching the cart source impedance into the load would only be relevant if you are trying to transfer the maximum power from source to load which is not the goal of a phono preamp. It would be like trying to match the load a speaker presents to the output impedance of an amplifier which can have an output impedance measured in milli-Ohms.
What you do want to match between cart and load is the conjugate match of the imaginary (reactive) part of the impedance so the cart sees a purely resistive load. The cart has a complex source impedance which may not be a simple series or parallel capacitive or inductive component but a combination of those elements. The complex impedance will most likely change with frequency as well, complicating the matching network calculations.
Perhaps what is needed is an S-parameter measurement file for the cart that can be used in a linear simulator to design an appropriate conjugate matching network. Most RF devices are spec'd this way and is the only practical way to design matching networks that work; absent this data, it's like trying to find your way out of a maze with your hands tied behind your back and wearing a blindfold. |
Dear @intactaudio : Thank's. I understand that normally the dielectric in SUT is air but I can be wrong. The only SUT silver wired I tested in my system vs SUT's cooper wired was the Audio Note Kondo that was compared vs the AT 1000T, Denon 340 and Denon AU-1000 and in all tests I prefered the cooper wired SUTs ( phono input 100k. ) and you the silver wired ones.
Maybe the SUT kind of wire is more or comes along with the room/system and owner targets. Different with speaker croosover inductors where silver is superior to cooper wired and ribbon shape over rounded ones.
Btw, the Kondo goes down to 2hz ! ! and Audio Note builded around the end of the 70's a SUT with an exceptional FR: 2hz to 200khz at -o.5db and 0.001% distortion. I never seen in the market and I don't know neither if was silver wired but probably not because was at the midle of Audio Note SUT line.
R.
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