This review was a result of months of listening and experimenting. Turned out to be much more involved (and interesting). Feel free to skip around.

• The SR4 – Design & Setup
• The Sound
• Comparisons
• Final Thoughts

But first…a little bit about the man behind the masterpiece.

Paul Hynes – The Eloquent Words of a Purist

The holy grail for me has always been to create a convincing dimensional and dynamic illusion of a live performance where my reference is always live acoustical music from a single performer to a full concert orchestra – not other manufacturers equipment. Get this close to right and other music genres work well too. The only commercial equipment I have ever purchased has been front-end related. For example record decks, tonearms and cartridges, CD, DVD and Blu-ray players. Everything else I have always built myself, initially before 1980 from other people’s designs then from 1980 progressively more of my own designs.

Obsession is a good thing for those with enquiring minds.

I have to admit to an obsession with power supply design and this has been my specialty alongside ultra-low noise signal processing (initially vinyl related then digital). I have probably spent more time and money on R&D than most (obsession again searching for the holy grail) and the voltage regulator circuitry I use on my SR power supplies is the result of all this effort over the years. It is the circuitry that gives me the best performance in my system. I have provided little information on the net over the years, as some of the design aspects are commercially sensitive.

I first used a high performance regulated power supply in 1980, which was designed by Michael Sultzer (from Sultzer’s article in Audio Amateur 2/1980). Prior to this, I used various integrated circuit three terminal regulators within my audio projects. Michael’s discussion on the effects of regulated power supplies on sound quality was sensible and his audible findings correlated well with measured performance. He proved that the power supply impedance should be as low as possible and the bandwidth as wide as possible to minimize any power supply inter-modulation distortion.

So Paul, what are your design goals?

The target is to provide a vast energy source relative to the needs of the circuit to be powered. The electronic regulator simulates this vast energy source by attempting to correct any fluctuations in the power supply caused by varying load currents.

When power supply interference mixes with the signal, it masks low-level information and causes inter-modulation with the signal. This destroys the integrity of the music signal. For the highest performance from audio electronics, great care is required in the design of the power supplies to minimize power supply induced problems.

The ideal regulator would present zero impedance to the load at all frequencies. This implies that the regulator error amplifier should have a transient response with infinite slew rate and zero settling time. At present this is impossible, however, it is possible to improve on the usual regulators used in audio applications by a large margin.

So…why is the regulator so important?

A typical voltage regulator is a DC coupled AC amplifier with its input connected to a fixed reference. A feedback loop senses the regulator output and compares it to the reference. If the load current changes, there will be a corresponding voltage change at the regulator output due to finite regulator output impedance. The feedback loop will attempt to correct this change via the AC amplifier. The time taken for this correction is governed by the AC amplifier’s transient response and settling time.

Further considerations are the effects of RFI and digital clocking breakthrough on the power supplies. In these instances, we are talking multi-megahertz frequencies often with fast waveform rise-times. At these frequencies and speeds, normal regulators are no longer working and can, in fact, make matters worse as they attempt to correct such errors.

They can overshoot their settling target and wobble about at different frequencies (ringing) vainly trying to catch up with themselves. This overshoot and ringing permeate the current flow paths, modulating the noise floor, which then transfers into equipment signal paths, polluting low-level signal information in analog circuits and adding uncertainty to timing and reference voltages in digital circuitry.

What type of regulator would be optimal?

With this in mind, it should be apparent that we require a regulator that is considerably faster when handling audio signals than first thoughts would suggest. You cannot expect a regulator with a transient response and settling time of microseconds to track a signal waveform with a rise-time of say 100 nanoseconds. However, if a regulator can track these waveforms, dealing with audio waveforms should present no problems.

Most audio equipment manufacturers use industry standard regulator devices in their products because they are readily available, cheap and generally easy to apply. Some benefits are offered by these products, notably, reduced power supply ripple breakthrough from the rectifier/capacitor power sources. This allows a much smaller capacitor to be used, which in turn reduces component costs considerably, more than offsetting the cost of the regulator itself. Multiple regulator systems can be applied more easily and cheaply, and once again these regulators can be significantly cheaper than a high-quality decoupling capacitor of sensible size. As you can see the main benefit of using these devices is essentially one of cost reduction. Whilst this is a laudable aim, most enthusiasts will generally prefer to look for performance improvement before cost considerations (within reason, acknowledging the fact that few individuals on this planet have unlimited budgets).