SUT - electrical theory and practical experience

My Johnson is very quiet without a SUT, speaking for myself only.

But seriously folks, Ralph (Atma-sphere), you have often mentioned the notion that high gain phono input stages need to be designed to be insensitive to RFI.  What design elements contribute to that good behavior?  Is it simply a matter of limiting the bandwidth?

@atmasphere 

That's a very thorough, well-considered assessment of the advantages and disadvantages of SUT.  Thanks for taking the time to share your knowledge with me / us!  

you have often mentioned the notion that high gain phono input stages need to be designed to be insensitive to RFI.  What design elements contribute to that good behavior?  Is it simply a matter of limiting the bandwidth?

@lewm I wouldn't say its any one thing. I've found that bandwidth (on the RIAA curve) is a good idea up to about 100KHz (I have an anecdote about that which taught me the importance of this).

Beyond 100KHz you get into RFI issues from the cartridge. That might not be a problem if the phono section input can handle the RFI without overloading. This is much easier to do with tubes than it is with solid state! If using solid state at that point I would say yes, bandwidth limiting is a good thing. You would have to be careful that any RF energy can't get rectified by a non-linear problem though! So to deal with this problem you'll be using several techniques to sort it out.

I mentioned that this is easier to do with tubes; the reason is that if solid state there is often a feedback loop involved. Its possible for the portion of the circuit that is causing the problem to be outside the feedback loop. The reason for that can be subtle; for example you'd think an opamp using feedback would be immune to this problem since the feedback is applied outside of the opamp. But if the opamp lacks the bandwidth, you can have a situation where the RFI comes in but isn't corrected because its outside of the passband of the opamp. So it distorts. The trick there is likely to not ask so much gain of the opamp but you have to be aware of the RFI problem in order to get that far...

Dear @drbond : In april of this year you started a more or less similar tread where all was explained about SUT and the like but obviously as in this thread too you have not a 100% understand of the whole subject.

Now, you decided to buy the CH phono stage with the " additional " power supply so what’s all about SUTs? Maybe you need tomatch the CH to a different amp. You diminished the JC 1+ maybe by its very low price, you will be surprised if you listen to it in the same way that Fremer/Atkinson were with the humble Stellar SS phono stage.

Could you explain a little? maybe you are thinking to change your CH fora SUT road?. I don’t know something makes no sense down there. You own the Lyra Atlas why not ask J.Carr if he prefers a SUT or an active high gain S phono stage?

""

but under near ideal circumstances, both would sound nearly identical.

Are there any inherent weaknesses in a SUT versus a transistor, or vice versa? ""

In your other thread and in this thread me and other gentlemans let very clear the differences with an additional disadvantage with SUT due that you need additional connectors and cables for that external SUT. You need to use your common sense too.

An about all that theory of the RFI is only that and happened 20-30 years ago but that mediocrity SS designs almost disappeared and I say " almost " because always are bad designs. Today designers learned. Bandwindth? your CH has an over 500 khz of bandwidth and the Channel D over 2 Mhz, Spectral over 1.5 Mhz , my Essential 3180 over 1.5 Mhz with no trouble at all.

Please read the M.Fremer Stellar 2,5K active high gain SS phono stage and additional read its measurements where J.Atkinson really was surprised by it RIAA accuracy that at least even the CH one and not only that but its very low noise levels and its incredible overload marginn at 30dbs in low gain and almost 20dbs in high gain position and you have all those for only 2.5K and makes MUSIC comparable to the Dartzeel that set you back 20 times over the Stellar price tag. Fremer listened using the SAT tonearm in continnum TT and the Ortofon Ana Diamond. Can you look in that review any SUT? why not?

COMMON SENSE, it does not need it due to its higher signal degradation.

R.

@rauliruegas 

I think a course in English comprehension would benefit you immensely, and allow you to contribute more positively to these forum discussions:

Firstly, the thread in April was a thread about phono stages for a particular turntable, and only peripherally and incidentally touched on SUT's, and did not go into the theory or discussion of what SUT's do to audio signal / SQ in any detail. 

Secondly, you hijacked that April thread on phono stages and ceaselessly posted about power amplifiers, which I surmise is due to your inability to comprehend what is written in English.  

Thirdly, I am still enjoying the CH Precision P1 with X1 power supply, and have no intention of changing that component, but I am intellectually curious about other approaches to phono signal, and why one approach is chosen over another, and @atmasphere was kind enough to share a very thorough explanation yesterday.  

In the future, I may get an SUT to use to plug into the MM input of the CH Precision P1, just to compare the SQ from the MC current input and the MC voltage input, or perhaps I'll get a second phono stage to compare SQ with.  This is just a fun hobby for me.