Soulution's resident circuit engineer Christoph Schürmann is a very soft-spoken and modest chap. His design ethos revolves around speed (which requires high bandwidth which challenges stability) and concomitant precision. With his unique fixed-gain voltage control amp performing up to 80MHz [left - the upright circuit boards connect via silver pins and the module is cast in synthetic resin] and 3-stage current buffer, the amplifiers' feedback loop has been shortened by a factor of 10 to optimize operational speed and minimize errors. His current sources operate with bandwidth from 10 to 100MHz and the impedances for his power supplies are held very low. "The signal passes through my voltage gain stage in approximately 10 nanoseconds with a max amplitude deviation of 0.1dB. To perform at this level of precision naturally requires constant thermal conditions."

Schürmann's goal for Soulution was to work outside the usual hexenring—or witches' circle—whose trinity of speed, bandwidth and stability is interconnected. Push one aspect, impinge on another. To truly push amplifier design forward meant devising a lower-gain topology that could guarantee complete measured stability regardless of load behavior or feedback. To prove his point, he furnished certain measurements he claims competitors would never publish as they can't approach them. More on those measurements on the next page.

High-speed circuits dislike right angles, hence Schürmann layouts favor diagonals or even curves.

Here are a few screen shots of his monitor.

 
 
 

The copper bus bars below carry up to 60 amps of current to the output terminals where output impedance is a low 89 milli-ohm for exceptional 5-figure damping factor.

The bipolar Sanken output transistors too mount to solid 6mm copper rails. "MOSFETs are popular because they're easier to work with than bipolars. I prefer the latter but to obtain their best does require overcoming certain challenges."

Soulution's architectures are always modular. The 740 CD player for example can easily be converted into the 745 SACD player by replacing its JPL-2580M Stream Unlimited CD drive with a TEAC/Esoteric SACD sled and adding SACD-specific conversion boards.

While the winds of fashion shifts in various markets to favor either CD or SACD machines at any given time, Soulution's platform responds elegantly. This eases inventory burdens.

The 720/721 preamplifier employs low-impedance relay-switched premium Vishay resistors for volume control and claims bandwidth from DC to 1MHz with a >140dB S/N ratio and >110dB channel separation.

The sub-enclosure on this particular preamp contains a prototype SMPS module on its right cheek which Schürmann was experimenting with in his lab to conform with the latest EU regulations that limit allowable standby power draw. While many EU imports silk-screen the CE or RoHS icons to their gear without costly laboratory verification papers in hopes of slipping through customs—they often do until a competitor reports them to a government lab test where they fail— a brand of Soulution's ambitions must be able to satisfy all regulations in earnest and on the spot upon demand. To remain in compliance, new legislation naturally might enforce partial redesigns of existing products but Schürmann considers that part of his job.

Another look at the copper bus bar array.
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