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About NanoSword

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  1. SR7
    A novel way to massively improve the SQ of computer audio streaming
    Hi romaz,

    as there is no information about the PH SR-7 on the internet, can you provide some basics as price, dimensions, voltages etc?

    Thank you.



    Here are some excerpts I've collected from Paul's e-mails to me over the past months. Hopefully, you'll find them useful as you make your own decisions. I've never personally met Paul (he is based in Scotland and I am in California) but based on numerous e-mail correspondences over the past year, I feel like I've gotten to know Paul pretty well and he has been a wonderful source of education for me. As you'll see from his correspondences, he is very articulate. He is also one of the nicest human beings I have met on my audio journey. I have spoken much of his SR7 on this thread and his power supplies really deserve a dedicated thread of their own but since this thread is about the things that "massively" improve either the microRendu or sMS-200 and since I consider his SR7 as the single most important component that I own that literally massively improves either of these NAAs, I feel it appropriate to to respond to your question comprehensively. Full disclosure -- I have no business relationship with Paul and I am a paying customer like anyone else.


    Here is his response to me more than a year ago as I was comparing my HD Plex and its LT1083 regulators to Paul's own PR3 regulator design:


    "The PR3 regulator topology used in the SR7 power supplies is my

    proprietary discrete component design optimised for high quality audio

    use. All the important audio related performance parameters of the PR3

    regulator modules are considerably better than the LT1083



    The PR3 series voltage regulator noise measurements using an HP3561a

    spectrum analyser specialized for low frequency measurement down to the

    sub 1Hz region


    The noise floor of 3561A is typically 15nV/sqrt Hz and the PR3 series

    regulator was around 44nV/sqrt. When the 3561A noise floor is factored

    into the measurement the PR3 series regulator would display lower noise

    than 44nV/sqrt.


    The ALW version of the Walt Jung ultra low noise regulator, which is the

    lowest noise of the generally available DIY regulator circuits, was also



    Here are the NF at 10Hz to 100 KHz:

    PR3 series reg – 44nV/sqrt. Hz

    ALW series reg – 70nV/sqrt. Hz

    (40 nV/rtHz = 5 uVrms).

    Measured from DC to 100 KHz the output impedance remains below 3



    Regulation operating bandwidth is from DC to >300 MHz allowing for device



    Transient response for a 5A load current change is typically

    <100nanoseconds and the settling time is also <100nanoseconds.


    Transient current delivery for PR3HD modules >30A.

    Supply line rejection >80dB DC to 100Khz (>150dB DC with double regulated PSU)

    I use Panasonic FC, FM and FR low ESR high ripple current, high

    temperature energy storage capacitors for excellent transient current

    delivery and long working life. Alternatives can be fitted but it is

    very important to ensure adequate power rating of power supply

    capacitors in high current linear power supplies like the SR7. The

    Panasonic capacitors are very well built and give consistently high

    sound quality in capacitor tests on various audio forums."

    Many have privately approached me with questions about how best to improve SQ and then stop me once I start talking about power supplies. Their response typically goes like this: "You don't have to convince me of the importance of good power, I already know this because I own an HDPlex." These folks have no idea. No offense to HDPlex but the model I own is nowhere in the same vicinity as the performance of my SR7. I also have a Teradak, Kenneth Lau, Paul Pang, iFi, and various DIY battery supplies that are now collecting dust. The only thing that comes close (that I own) is the LPS-1.


    As I started to talk to Paul about the importance of the output impedance of a PSU, here was his informative response:


    "Power supply output impedance is an important parameter, as are transient response, settling time, operating bandwidth and noise. For exceptional power supply design it is important to consider all of these parameters and optimise them to the best of your ability. This is what I do. The ideal power supply would have zero impedance at all frequencies of operation as you cannot develop any voltage into zero impedance no matter how much current passes through it. In the real world all circuits have some level of impedance and any current passing through this impedance will generate a voltage fluctuation, which in reality becomes an additional noise source in the system, which degrades signal integrity. It is therefore important to minimise the impedance to reduce this disturbance to the lowest level. This impedance reduction is usually achieved by an error amplifier using high levels of negative feedback, which introduces all manner of problems with operating bandwidth, transient response and settling time. This is a big subject to consider so I will not go into detail here. Suffice to say I do not use typical circuit topologies in my voltage regulator designs to achieve low impedance over a very wide operating bandwidth."


    As you've seen above, Paul lists his measurements for these parameters. No one else seems to do this either because they don't have the measuring equipment to do so or they don't believe these parameters are even important. Without measurements, it's hard to even know how to shop for a good PSU and so the end user is forced to do his/her own listening comparisons or else make a purchase based on speculative comments.

    Here is his response regarding the importance of using high quality, expensive discrete components. Paul's supplies are not inexpensive but it's not because it's all going into his pocket. Most importantly, IMO, the performance for the dollar is there:


    "Some industry participants have been minimising the importance of “expensive” discrete component high performance voltage regulators in their marketing and concentrating their marketing stance on other parameters. I have to disagree here as I have conducted extensive testing in these areas over many years. Everything you use to build a power supply will have a sonic signature that will imprint on the achievable sound quality. Using low cost industrial voltage regulators with limited performance will just bottleneck the overall performance that is achievable and no amount of attention to detail in the other areas will override this."

    Paul makes 3 lines of PSUs, from the SR3 to the SR7 and here is how he describes them:


    "The SR3 was originally custom designed for a customer to improve on the performance offered by the Optima Red Top car battery used for the Altman Attraction DAC. As I foresaw additional sales for the SR3 for a wider variety of equipment I wanted it to be small enough and light enough to ship world wide via the Royal Mail small packet rate (under 2Kg) and of reasonable price. The mains transformer was the best of the “off the shelf” transformers available in the UK and the “off the shelf” chassis limited the transformer size to 60VA. The current PHD SR3 is rated at 30W continuous delivery and 240W transient delivery.


    The SR5 was designed in response to requests for Mac Mini rated power supplies. The power rating had to be 80W continuous and it can also provide 350W transient delivery. This is achieved by increasing the mains transformer rating to 160VA, additional energy storage capacitance for robust power delivery with large dynamic load transients and the design of a custom chassis to house this and the electronics and heat sink required for this power upgrade. I also increased the power ratings of the Schottky Barrier rectification and the output stage device to provide the power rating with comfortable margins for safety and long life. More space within the chassis allowed me to design a mains transformer that would address the shortcomings of “off the shelf” mains transformers. In particular, core saturation is a big issue as the transformer operation stalls when this happens. Other big issues are electrical and mechanical noise. The SR5 and SR7 mains transformers are carefully wound on manually operated winding machines using over sized grain orientated silicon steel cores and high quality wire to minimise these issues. They are designed for low impedance operation and can deliver very large transient currents to the load.


    The SR7 is essentially a higher power version of the SR5 with increased ratings for all power devices and a larger 250VA mains transformer giving a 125W continuous power rating and a 480W transient power rating for the more power hungry applications.


    Many customers asked for a “Multirail” power supply to reduce space requirement for multiple power supplies in systems and also to reduce overall cost so I then designed the SR7 Multirail with up to four galvanically isolated supply rails to avoid interaction between the various items of equipment to be powered. The SR5 can also be configured as a Multirail but space limits the number of rails to two.


    The best way to describe the performance between the three power supply levels is to use the car engine analogy. A small runabout with a 1.2 litre engine, a hot hatchback with a 1.6 litre fuel injected engine, a larger family saloon with a 3 litre fuel injected engine and a sports car with full engine management. Braking systems for these cars will be suitably rated to cope with the engine power. All four cars will get you from A to B but the ride will be progressively more responsive, dynamic and stable as you go up the range of cars. The runabout is the equivalent of a low cost power supply upgrade, the SR3 is the hot hatchback with acceptable all round performance and a lively drive, the SR5 is the 3 litre family saloon with a more stable but responsive drive and the SR7 is the sports car with even better performance.


    As you go up the range in power supplies this translates into the traits you were hearing at the listening trials. The musical performance in all areas just improves with a more stable three dimensional presentation that is more robust when the going gets busy with the better power supplies."

    More recently, he stated it to me this way:


    "The SR range of high performance power supplies were designed for powering both analogue and digital audio and video equipment. The same proprietary ultra low noise high performance discrete component voltage regulator circuit topology is used in the SR3, SR5 and SR7 power supplies. The SR3 uses a standard 50VA mains transformer, the SR5 uses a custom manufactured 160VA mains transformer and the SR7 uses a custom manufactured 250VA mains transformer. The SR7MR uses a custom manufactured mains transformer with up to 500VA rating depending on the overall rail requirements. The custom manufactured mains transformers use oversized grain orientated silicon steel cores and are wound to avoid core saturation in use and to operate quietly both electrically and mechanically. Schottky Barrier rectifiers are used throughout the range, as they do not generate reverse recovery transients and their associated harmonic distortions.


    The error amplifier used in the voltage regulator modules has the following specification :-


    Noise voltage < 0.5 nanovolts root Hz

    Operating Bandwidth > 300 Mhz

    Supply line rejection > 80 dB DC to 100 KHz

    Output impedance < 3 milliohms DC to 100 KHz

    Transient response and settling time < 100 nanoseconds


    As the SR3, SR5 and SR7 all use the same high performance regulator circuit topology they all have a similar sonic signature musically. Moving up the range allows better quality lower impedance mains transformers and up-rated rectification and regulator output stage providing a reduction in power supply output impedance, which in turn reduces interaction with the load. The increased energy storage capacitor bank also reduces rectifier ripple noise and RFI break through from the mains supply. Another benefit of the increased energy storage capacitance is with transient response and settling time. The net effect musically is to provide progressively larger, more stable and more robust soundstage particularly where large dynamic load current swings occur, as well as, a lower noise floor and improved timbre and temporal accuracy.


    These power supplies are available with fixed voltage output from 1.6v to 30v or variable voltage output with a 10 volt span on voltage setting, within this range, using the precision adjustment potentiometer internally situated on the regulator module.


    Continuous power output ratings – For fixed output voltage versions the SR3 provides 25W, the SR5 provides 80W and the SR7 provides 125W and the SR7MR chassis can support up to 250W spread across the rails. The SR5 can support one 6A module and the SR7 can support one 10A module. The output voltage and output current can be specified within this power rating using the formulae :-


    V = W/I

    I = W/V


    Where V is output voltage, W is the available power in Watts and I is the output current in Amps.


    If you require help with power supply specification I will be pleased to help you.


    For variable output voltage versions of the power supplies, set at the maximum output voltage of the range, the SR3 provides 25W, the SR5 provides 80W and the SR7 provides 125W. Lower voltage settings than maximum will increase the voltage across the regulator output device, which will increase the heat generated in this device. To maintain safe operating temperatures and long term reliability the current rating should be de-rated by 8% per volt when reducing the output voltage level on variable output voltage versions.


    The SR5 and SR7 power supplies are available in Multirail versions SR5MR and SR7MR with galvanic isolation between the supply rails to avoid ground return current intermodulation (ground loops) where more than one item of equipment is powered from the same power supply. The SR5MR can support one 6A regulator module and one 3A regulator module or two 3A modules. The SR7MR can support one 10A module and up to three additional 3A modules or two 6A modules and up to two additional 3A modules.


    XL ultra low impedance (< 1 milliohm) connectors and fine silver internal wiring between capacitor banks, regulator modules and the output connectors, can be fitted to the SR5 and SR7 power supplies.


    The SR3, SR5 and SR7 single rail supplies are also available in DR versions where two of the high performance voltage regulators are cascaded to a give supply line and rectification interference rejection exceeding 150 dB from DC to 100 KHz. This provides lower overall noise levels than the standard power supplies.


    Current Prices 200117


    SR3 £300

    SR3DR £500


    SR5 £600

    SR5XL £678

    SR5DR £800

    SR5DRXL £885

    SR5MR2 £800

    SR5MR2XL £970


    SR7 £750

    SR7XL £870

    SR7DR £950

    SR7DRXL £1080

    SR7MR2 £950

    SR7MR2XL £1190

    SR7MR3 £1150

    Here is his pricing for his DC leads:


    Current Prices 200107


    All prices are for1 metre lengths with a Switchcraft DC plug. Alternative lengths and connectors can be quoted for if required. Cable impedance reduces with higher current rating. XL ultra low impedance (< 1 milliohm) connectors can be fitted to the SR5 and SR7 DC Leads.


    3A current rating :-

    DC3C annealed copper with Teflon insulation £050

    DC3FS annealed fine silver with Teflon insulation £085


    6A current rating :-

    DC6C annealed copper with Teflon insulation £075

    DC6FS annealed fine silver with Teflon insulation £145

    DC6FSXL annealed fine silver with Teflon insulation £186


    10A current rating :-

    DC10C annealed copper with Teflon insulation £100

    DC10FS annealed fine silver with Teflon insulation £229

    DC10FSXL annealed fine silver with Teflon insulation £270

    There is also the option for Paul to make you a double regulated PSU (with cascading regulators) and this can be discussed with Paul for those who want his very best. I cannot yet tell you what this sounds like because I haven't received mine yet. Considering the performance I am getting from his SR7, it is my opinion that this is some of the best money I have ever spent on audio. Without question, quality is the foundation of anything that is good in audio. Paul does not have a presence here on CA and for those who wish to correspond with him, you can do so via e-mail at [email protected].

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