If you’re curious about the benefits of using a linear power supply and how they work, check out my short overview here.

The Paul Hynes SR7s are known to be the best and most coveted power supplies in the world. The downside? They’re pricey and requires upwards of 8+ months to build. Paul knew they were cost prohibitive but wanted to give audiophiles a taste of what he strived so long to accomplish. Understanding the importance of this mission, he reshifted his focus onto a new project – and the SR4 was born.

The compact, single-rail SR4 was inspired by the popular demand for a more affordable, high-performance supply. The aim was to get as close to the performance of the standard SR7 as possible – without breaking the bank.

What’s so special about the Paul Hynes power supplies?

For one, Paul Hynes is extremely selective of the parts he uses, is constantly improving regulator topology, and a stickler for supply stability. They’re currently all hand-built and meticulously tested before shipment.

But there’s more…

  • Custom wound transformer
    • Offers higher levels of performance over the off-the-shelf toroidal.
    • SR7: The mains transformers are not used in the standard way as they are configured as balanced mains isolation transformers and they are also built on oversized cores.
  • Proprietary ultra-low noise, high-performance, discrete voltage regulator
    • Undoubtedly a major ingredient in Paul Hyne’s secret sauce and one of the reasons why his power supplies sound so good.
  • Large chassis for thermal management
    • Those regulators generate an enormous amount of heat. Chassis selection is critical for maximum dissipation and optimal layout.
  • High Power Supply Rejection Ratio (PSRR)
    • Generally difficult to keep low, especially at higher frequencies.
    • Both the SR4 and the SR7 should provide > 80 dB supply line rejection from DC to 100khz with a gradual reduction with an increased frequency above 100Khz.
    • The SR7DR would theoretically reach 160 dB over the same bandwidth, however, there are always losses due to stray interaction. So it’s tentatively 150 dB for the DR version. The SR7DR should provide the finest performance due to the much higher supply line and rectification noise rejection than either the SR4 or the standard SR7.
  • Insanely low output impedance
    • The output impedance is typically 3 milliohms from DC to 80 KHz and supply line rejection is > 80 dB over the same bandwidth and is still > 50 dB at 1 Mhz.
    • This demonstrates the regulator’s ability to manage the load, regardless of frequency.
    • How is it measure? The output impedance of the SR voltage regulator topology was measured by loading the regulator output via a modulated high power current source at varying frequencies. The measurements were taken between the regulator output sense node and the 0v reference star. Obviously connecting equipment via lengths of wire is going to swamp the low output impedance of the regulator, however, the low regulator output impedance is still valid as it reduces interaction at the regulator end of the wire compared to a regulator with higher output impedance.
  • Enhancement Options – These don’t apply to the SR4 but good to know when you’re looking for an SR5/SR7.
    • Double regulation (DR)
      • The benefits of DR provide a much higher supply line rejection and rectification artifact rejection than a single regulator alone – approx 150 dB from DC to 100KHz with a gradual reduction at higher frequencies.
      • DR is currently only available for SR5 and SR7 power supplies.
    • XL
      • The XL construction is only available on SR5 and SR7 and uses fine silver wiring for all internal DC wiring and Jaeger military specification DC connectors on the chassis and the power supply end of the matching fine silver DC leads.

Paul Hynes SR4 Build, Design, and Features

  • Single rail supply – Perfect for powering digital interface equipment including:
  • Voltage selection
    • 5V
    • 7V
    • 9V
    • 12V
  • Output current – 2A continuous, 20A transient
  • Design
    • Uses the same ultra-low noise high-performance discrete component voltage regulator as the highly regarded SR5 and SR7 power supplies.
    • The SR4 mains transformer is configured as a balanced mains isolation transformer to provide exceptional mains-born interference rejection like the SR5 and SR7 power supplies.
    • The output DC connector is a 4 pin gold plated Neutrik XLR and there are two metallurgy options for DC leads, annealed copper (DC3CXLR) or annealed fine silver (DC3SXLR).
      • The negative output of the DC isn’t grounded to AC ground to prevent ground loops.
  • Replaceable fuse
    • You have the option to tune with your own audiophile-grade fuses such as the ones from Synergistic Research or Audio Magic Beeswax, etc.

The SR4 chassis comes in anodized black or silver (black at additional cost). It’s not the most attractive chassis (looks like an external hard drive enclosure), but it’s unobtrusive and easy to fit into a system. The DC cable, on the other hand, is beautifully braided and would be something I’ll proudly to wear around my neck. Bling bling!

Equipment & Setup

  • Power supplies
    • Paul Hynes SR7
      • Dual 12V rails
    • Paul Hynes SR4
      • 5V, 7V, 9V, 12V
      • 2A continuous, 20A transient
    • SOtM sPS-500
      • 7 – 19V
      • 50W
      • 5 amps @ 7V, 9V, and 12V
      • 3.3 amps @ 19V
    • UpTone Audio UltraCap LPS-1
      • 3.3V, 5V, 7V (1A max)
    • Linear Solution LPS (the one that comes with The Linear Solution TCXO switch).
      • The TCXO sounds great and is currently my reference ethernet switch.
  • Grounding
    • SR4 – I didn’t ground the SR4 at the barrel
      • From Paul: Grounding the SR4 0v via the barrel on the DC plug should not harm the SR4, however, it may create a ground loop between equipment and other power supplies.
      • Multiple ground paths in a system can cause inter-modulation around the various ground paths, which may affect the overall sound quality adversely by increasing noise floor modulation in the worst-case scenario.
      • It is difficult if not impossible to predict the effect of this with so much equipment available with widely differing internal design, but there is no harm in trying this out. If it sounds better with the earthed 0v output fine, if worse then remove this local earth.
  • Power Cords
    • Audience Au24 SX
    • High Fidelity Cables CT-1 Ultimate
    • ZenWave Audio Furutech DPS-4
  • DC cables
    • With the exception of the Paul Hynes DC3CXLR used with the SR4, I used ZenWave’s Neotech 6N Copper DC cables with Oyaide plugs exclusively.