SUT - electrical theory and practical experience

Look, the main SUT limtation vs an active high gain SS alternative is its way limited  frequency bandwidth

If you are using opamps, you'll need a fair amount of feedback and that feedback will correct phase shift. So even though an opamp can be really wide bandwidth, it becomes less important because phase shift is minimized.

When you have a passive device or if the circuit is zero feedback, that's when you need the bandwidth in order to prevent phase shift. Now its well-known that the smaller you make an audio transformer and if that transformer does not have any DC in its core, its actually pretty easy to get wide bandwidth, often well past 100kHz. 

Put another way, the reason to have wide bandwidth is to get low phase shift in the audio band if you don't have any other method (such as feedback) to control it.

The concern IMO isn't the high end! its how well it goes low. But again with small audio transformers this is fairly easy to do.

Dear @lewm  : This is  the Denon design explanation, it's interesting to read it by any one:

 

""" 

 DENON has already released the DL-1000A, the highest grade cartridge, but in order to fully demonstrate the outstanding music playback capabilities of this DL-1000A, we have developed the AU-1000 as the highest model of step-up transformer. I did.
In order to boost the minute music signals sent from the cartridge, physical characteristics such as frequency characteristics were pursued, and countermeasures against external induction, i.e., strict shielding of the transformer unit and main unit, anti-vibration structure, connection cords, etc., were thoroughly examined in detail. and improved the degree of perfection.
In addition, in terms of sound quality, we have repeated sufficient listening tests to create a product worthy of the name of "the highest peak of step-up transformers."

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Features

1. Basic design born from thorough pursuit of sound quality.

For the transformer core, under strict material management, special-shaped large permalloy thin plates that pass strict specifications are laminated . Magnetic permeability, which is the basis of transformer quality, is about 1.5 times higher than conventional products (compared to our company) in the bass range, and achieves high saturation magnetic flux density over the entire .
A special split sandwich winding reduces the line-to-line capacity and extends the high range. In addition, a primary winding that is about 1.4 times thicker than conventional products (compared to our company ) is used to reduce resistance loss. Combined with the high saturation magnetic flux density, the dynamic range is wide, realizing a rich sound reproduction .

2. Thorough pursuit of sound quality with a simple structure.

Since it is dedicated to the MC cartridge DL-1000A, the impedance selector switch and intermediate taps have all been eliminated, and the structure to improve sound quality.

3. Multi-shield structure that is resistant to externally induced vibration noise.

A single transformer is double-shielded with a permalloy shield case, put in a thick gunmetal case, and fixed with a filler. Also, since the LR channels are wired independently in separate gunmetal cases, there is no crossover of wiring. Furthermore , the entire body, including the input/output pin jacks, is covered with a thick casting shield case and can be used as a high-grade universal transformer.

 

I owned that maybe the best Denon cartridge ever and when I bougth the cartridge in Laredo, TX I did not know about the Denon SUT.

 

R..

Here the DL 1000A ( btw, one of the J.Carr vintage cartridge favorities. ):

 

Main features of DL-1000A

■ We challenged the limits of weight reduction and achieved an astounding effective mass of 0.077mg.

The vibration system of the DL-1000A faithfully traces the complex and fine sound grooves, so a new material, New Amorphous Boron Pipe, is used to thoroughly reduce the weight of the vibration system, resulting in an effective mass of 0.077mg. realized. (DL-305 is 0.168mg) In
addition, coupled with light effective mass and well-balanced high compliance, extremely stable tracing is performed not only in the mid-low range, but also in the fine sound grooves in the high range. It is extremely rare to deform the sound groove. As a result, the playback band extends to an unprecedented ultra-wide band of 20Hz to 110kHz.

(1) High rigidity, ultra-thin and lightweight new amorphous boron pipe cantilever

DL-305 and DL-207 use amorphous boron, which is said to be the most ideal cantilever material and has a large specific rigidity. A cantilever with a thickness of 0.3 mm, a thickness of 0.023 mm, and a length of 4 mm is used.

(2) World's smallest micro stylus chip

Reducing the weight of the stylus tip, which is positioned at the forefront, has a great effect when reducing the effective mass seen from the tip of the stylus. It was considered very difficult to make a stylus chip micro, but we have improved our processing technology and accuracy to create a 0.06 mm square micro chip. (Approximately 1/2 of DL-303/305) The
shape is a special elliptical needle that has been precision machined.

(3) Uses a small cross-shaped winding frame and extra-fine copper wire

The cross-shaped winding frame can reduce the mass, and the left and right channel generating coils can be wound independently and symmetrically, and the dynamic balance during vibration is good, the sensitivity difference between the left and right channels is small, and uniform characteristics can be obtained. has two major advantages. The well-balanced generator coil uses ultra-fine copper wire, which advances the significant weight reduction of the vibration system.

(4) Like a feather. Stable tracing with record-friendly stylus pressure of 0.8g

The dramatic reduction in effective mass enables well-balanced, high-compliance, and a light stylus force of 0.8g shows sufficient tracing ability, providing stable tracing even for high-level cutting records. We will realize

(5) Flat ultra-wideband reproduction by 2-way damping system

In addition to broadening the bandwidth by reducing the effective mass, coupled with the adoption of DENON's original 2-way damper, flat frequency characteristics up to 110 kHz are realized, and reproduced sound with good energy balance can be obtained.
In addition, good temperature characteristics (small difference in sound quality between cold and warm regions) is another feature of 2-way damping that cannot be overlooked.

■ Powerful power generation structure

A samarium-cobalt magnet (with a magnetic energy product several times that of conventional magnets) is used in order to obtain a compact, lightweight, and strong air-gap magnetic field.
The weight of the cartridge has been reduced to 6g, but reducing the weight of the cartridge has the effect of reducing the effective mass seen from the position of the stylus of the tonearm, and the ability to follow the warp and eccentricity of the record. have a great effect on increasing

■ Emphasis on stylus pressure vs. output voltage characteristics

DENON attaches great importance to stylus pressure vs. output voltage characteristics as one of its basic performances.
The vibration system of the cartridge receives extra changes due to warpage of the record, etc., and the stylus pressure constantly changes. For this reason, if the linearity of the power generation system is poor, the output voltage will fluctuate greatly or be modulated, making it impossible to obtain a clear reproduced sound.
The DL-1000A has excellent linearity in the power generation system, and in combination with its excellent tracing ability, you can always obtain high fidelity and stable reproduced sound.

■ Promoting non-resonance with a strong frame structure

In order to fully demonstrate the performance of the excellent vibration system, we have adopted a strong frame structure that is non-resonant.
The frame, including the powerful magnetic circuit and output terminals, is made of hard resin containing glass fibers and a machined light alloy base.

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To amazing tracing ability
World's lightest - effective mass 0.077mg

The effective mass of the vibration system, which has been thoroughly refined and polished, has achieved the lightest weight of all cartridges, 0.077mg. At the same time, the world's largest dynamic compliance of 20 x 10-6 (static 50 x 10-6) cm/dyne is achieved. I just got amazing tracing ability. With this new dimension of tracing ability, you can reach the musical depths of record grooves that you could not reach before, and draw out all the musical information that could not be reproduced in the past.

■ Comparison of sound groove traces

■ DL-1000A output voltage and crosstalk versus frequency characteristics

■ Comparison of frequency characteristics due to temperature change

■ Cartridge case can be used as a cartridge keeper

The DL-1000A is delivered in a velvet-covered case. This case can store 5 cartridges with shells.
The stand on which the DL-1000A is installed can be used as an audio stabilizer after removing the cartridge.

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DL-1000A major specifications

• Power generation method: Moving coil type
• Output voltage: 0.1mV (1kHz 5cm/sec horizontal direction)
• Left and right sensitivity difference: within 1dB (1kHz)
• Right and left separation: 30dB or more (1kHz)
• Electrical impedance: 33Ω (20kHz or less)
• Compliance:
  Record reading 20×10-6cm/dyne (100Hz)
  Static reading 50×10-6cm/dyne
• Transducer effective mass: 0.077mg
• Needle tip: 0.06 mm square solid diamond special elliptical needle
• Stylus force: 0.8g±0.1g
• Reproduction frequency range: 20Hz - 110kHz
• Compatible load resistance: 100Ω or more (40Ω when using a transformer)
• Weight: 6.0g  and is an exeptional tracker with its very high compliance over 30cu.
•  

I still own the case too.

"" The concern IMO isn't the high end! its how well it goes low. ""

 

with the rigth MM stage design way better that any tube phono stage. You have to listen any of the SUTs I named here.

 

I forgot that I owned the Supex and left it goes due that in those times my knowledge levels were still lower than today. Shame of me for that.

 

R.