SUT - electrical theory and practical experience

Dave Slagle is well a known and respected manufacture of custom SUTs and does an excellent description of the theory and details - intact audio.  Beyond that he winds with both copper and silver, and each will have a different perspective to the music.  There are variations in core material that can influence the sound with each SUT manufacturer often favoring one over another.  

My own experience has been quite positive moving from a solid-state phono-preamp to a Tron Seven Reference with SUT and tubes and was quite surprised on the overall improvement, much more than incremental - equally quiet with better bass and overall extension and soundstage.  But the devil is in the details, and results can vary.

Not proclaiming to be any expert, but when discussing 'rise time' the traditional engineering parameter s 'slew-rate' dvt/dt = X-volts/micro-sec.  And once you are talking about slew-rate there is some pretty established science associated with it such as that described in the following recognizing that the 'amplifier" gain (be it SUT+tubes or solid state) has an effect and that to produce a specific frequency there is a minimum 'slew rate'.

Slew Rate: What is it? (Formula, Units & How To Measure It) | Electrical4U

AN-346 High-Performance Audio Applications of The LM833 (Rev. D)

Phono Preamp Project - Graham Slee Audio Forum | HiFi System Components - Page 2

And in the Texas Instruments document there is this paragraph:  

"In addition to the amplitude response errors (which can be made small through careful design), the lack of a continued rolloff can cause distortion in later stages of the audio system by allowing high frequency signals from the pickup cartridge to pass through the phono equalizer without sufficient attenuation. This is generally not a problem with moving magnet cartridges, since they are usually severely band-limited above 20 kHz due to the electrical resonance of cartridge inductance and preamp input capacitance. Moving coil cartridges, however, have very low inductance, and can produce significant output at frequencies as high as 150 kHz. If a subsequent preamplifier stage or power amplifier suffers from distortion caused by slew-rate limitations, these ultrasonic signals can cause distortion of the audio signal even though the signals actually causing the distortion are inaudible."

@rauliruegas,

For the record and no pun intended, TI did not exclude wide bandwidth MM.  Their written statement was "This is generally not a problem with moving magnet cartridges, since they are usually severely band-limited above 20 kHz...".

Otherwise, your preamp spec with slew-rate 350 V/us and 1.5MHz bandwidth mathematically (using the equation to determine slew rate at frequency) is capable of a peak voltage (at 1.5MHz) of about 3.7V.  Any more than this and at 1.5MHz, the amp becomes unstable.

What does this mean in real-life?  Well, that's a good question.  There are obvious 'designers" such as Goldmund and Spectral WELCOME to Spectral Audio'sHome Page who adhere to very high 'speed' high slew-rate (Spectral is >1000 V/us with bandwidth 1.5 MHz) designs as the optimum.  While others do not.  

The 'bandwidth' (no pun intended) of audio design and followers of each is equally wide (no pun intended).  For one to stipulate that one is better than the other, IMHO is an exercise in futility given the wide variation in just individual sensitivity to sound which academia has indicated can be a factor of 10:1:  

Consider what is written page 16 – of Microsoft Word - P406POM_Lect5.doc (illinois.edu) UIUC Physics 406 Acoustical Physics of Music ©Professor Steven Errede, Department of Physics, University of Illinois at Urbana-Champaign, Illinois 2002 - 2017. The Human Ear ⎯ Hearing, Sound Intensity and Loudness Levels (78) "The time-averaged, or RMS sound intensity threshold of hearing (@ f = 1 KHz) is: ~ 2.5x10-12 RMS Watts/m2 = 2.5 RMS pico-Watts/m2. Individual people may hear better/worse than the average person, and so threshold of hearing from one person to another can vary as much as 1/10 or 10X this!!!".

Take care and best wishes for the holidays,

@lewm,

Not to take too much of a tangent from the intent of this thread, but this article should clarify sound intensities in watts per meter squared with the more commonly used sound intensity levels in decibels (dB) - Sound Intensity and Sound Level | Physics (lumenlearning.com).

Take care and best wishes for the holidays,

@rauliruegas,

You have taken what I said completely out of context.  What I was trying to say is that based on the two values you provided which was only the slew rate and the bandwidth, that by the equations the amp would become unstable at a specific voltage with one caveat (as addressed in the documents I linked) that designing the amp for peak voltage above that threshold maintains stability.  I also linked the Spectral specification where they specify all three values - slew rate, bandwidth and peak voltage.

So, I never stated that your preamp would be unstable above 1.5Mhz and now better appreciating how you interpret these items, should I ever conversate with you again, I will endeavor to be far more specific to prevent any misunderstanding. 

Peace on Earth and Good Will to All