SUT - electrical theory and practical experience

Btw, @intactaudio  : you capacitance parameter of 80pf coukld be not real to make SUT measurements as the 300k load.

Normally what sees the MM stage + SUT is a load of 47k and capacitance around 200pf. Then measures arwe different that with your " choosed " parameters.

Unfortuntaelly cable manafucterer almost never gives the cable capacitance but almost all are higher than 150pf and even over 200pf.

I think everyone who prominently recommends SUTs on this forum also cautions to select low-capacitance cables. There are ample phono-targeted ICs optimized for low capacitance. Select one of those models, keep the run short (ideally under 1m), and hitting a capacitance under 80 pF is quite easy.

Here’s my current assessment, which has been nicely summarized by @intactaudio :  basically, the cartridge is naturally developed as a current generator,

I was pretty convinced of ^that^ myself, but I still have some lingering confusion.

however for the past decades, phono stages were created to unnaturally transform the cartridge into a voltage generator by adding the load in the phono stage.

Unnatural is a bit subjective. If one shoves the current across a resistor then they can measure the voltage across the load like ohms law states. Ohms law seems like it is “natural”.

 However, when the cartridge operates as a current generator, no external arbitrary loading needs to be added to the signal created by the cartridge.  So, it seems,  based on my limited knowledge, that the current based phono stages would be most naturally associated with phono cartridges.

Many people use the Sutherland, and other trans -impedance phono stages, and love them. Usually with carts that have a very low output impedance.
And they do have an allure.

And many phono stages use a voltage based design, and/or SUTs and love them.

I was leaning heavily towards the Sutherland, but got a phono stage with SUTs built in, mostly because I liked the look of it, and it had two inputs.

if we look at a step up transformer, with an input to output ratio of 1:2, then we see that the voltage is doubles, and the current is halved.
If it is 1:20 then the voltage is x20 and the current 1/20.

A cart does not look too dissimilar as the input winding is serviced by the magnetic field of the magnet. The magnetic flux varies with the cantilever movement.
The output winding is the coil.

• When there is a lot of windings, like on a MM, we get more voltage and less current. (Probably better for a voltage based amplification.)
• When there are fewer windings we get less voltage and more current. (Maybe it is better for a current based amplification?)
• Then there is a middle ground with a bit higher output voltage or with a higher output impedance were it seem like it is unclear and all bets are off.

^This^ is not much of an answer, other than the choice of phono stage sort of relies on a cartridge in front of it.

And in this case we sort of need to “put the cart before the horse”.
Or…
We already have the selected phono stage, and we damned well better select a cart that will work with it.

In other cases, there are individuals who already have the selected Cart'.

In some cases, there is more than on Cart' in the collection of desirable models.  Again, in some cases, the users of the Cart/Cart's are expectant that their Phono Signal Path is optimised for the Cart'/Cart's to present at their best.

To assist with my experiencing a Cart' used in various operating conditions, I have a Phon' with a Very Good Quality Bult in MC Stage, that allows the Cart' to be used in multiple configurations in relation to Input Capacitance, L+R Channel Gain, Input Impedance. This device pretty much allows for a Cart' to be used, whilst subjected to a reasonable number of operational parameters.

 This same Phon' is a loaner Phon' and has been used with Ortofon's up to Windfeld Level, Miyajima and an AN IO.

The Phon' is not a lacking in SQ device, it is quite impressive, it has been used as a loaner in other systems for lengthy periods of time.

With a Head Amp attached to the MM Stage in my system, it has presented certain types of music with a Jaw Droppingly good account of itself.

In comparison to other Phon's using a SUT, it does not Wed to the SUT used, in a way that is as notable for the impression being made as with another Phon' > SUT in use

All the Cart' owners of the ones listed above have their own Designs for the Phono Signal Path, and each have their own unique configuration for the Phon' > SUT or Phon' > Head Amp. A Phon' with a Built-In dedicated MC Stage is welcome but not the preferred end game device.

The outcome being referred to, is one sharing similarities with the one that is seemingly the most prevailing within this Thread.

It does look like the difficulties with reconciling the math for the electronics and the rabbit hole leading to oblivion, commonly referred to about using SUT's only causes concern to those who want to Cudgel and Beat the methodology of the signal path being produced with a Technical Challenge.

The other side of the fence on lookers, especially those who have adopted the method of using a SUT or Head Amp, are using the reports made, looking to be quite pleased with the at hand option, to have a simple to use device, that is quite effective at offering methods to fine tune a particular presentation via a SUT or Head Amp, that is producing a presentation that has an attraction.

It is this, that is certainly one the motivators to avoid the usage of a device that is with limitations in how it can be configured, especially the type of limitation that is on offer from a dedicated MC Stage as the only option to be used.

The attraction to the method of using at hand options for working with electrical interfaces within the Phono Signal Path, is as satisfying as the ones used by myself for working with the Mechanical Interfaces required to produce a much improved environment for the LP Album to function in and the efforts made to use a Vinyl Material that is as purified from contaminant when in use as I can achieve.  

… , L+R Channel Gain,…

@pindac is a gain imbalance common in cartridges?

(I have a cart with some channel imbalance, hence the question.)

I am not educated enough to answer your question, these are the types of question I would take direct to my Third Party Cartridge Service I depend on.

Third Party Cartridge Services from what I have discovered through investigation and discussion with the Technicians does suggest there is a Channel Imbalance being checked and corrected as part of the Serice on offer.

There are Third Party Services who are happy to show evidence of their work, and some will put out photos of the Readings that are being achieved as part of the refurbishment work.

 My reasoning for the purchasing a Phonostage with a L+R Channel Gain Control, is to do with my totally trusting the Designer /Engineer and accepting the options incorporated into the device to deliver as per the designer's intent.

Additionally, as I am usually working with Dual Mono Volume Controls in the Pre- Amp's used and will one day soon have a my New Design Balanced / Single Ended Pre-Amp' Built, to be used with the Modified Power Amp's, which will have a Balanced / Single Ended Input, the option to tweak a loading on a Channel was to me a worthwhile tool, as the conversion to a Balanced Signal Path as the additional option has been projected for a very long time. 

I am avoiding the subject of Phon's and Balanced Signal Paths at present.