review of the 5V "Kingrex MK2 PSU" used in USB
Jan 15, 2013 at 3:58 PM Thread Starter Post #1 of 41


Galvanically isolated his brain
Apr 23, 2004
Hi there, it's been a while that I didn't post a review and I've been messing around with third party USB PSU's for quite some time now(I'd even dare calling it an OCD at this point
)....several followers of my Stello U3 thread asked me for further details and other Stello U3/DP1 claimed to hear drastic SQ improvements with cleaner PSU's so here we go! I'm only glad to share my modest "trial and error" real-world experience with feeding a cleaner PSU to USB audiophile equipment on my favorite audio-related forum

Long story short, after all the aforementioned "trial and error" I went through, google was kind enough to direct me to this thread that explains rather clearly what I had been up to on my side:
So we're talking about this $8 little fella that saves the day:
Mikrotik is a company that deals with WiFi routers and such, so this cable comes with all the shielding you would expect from a USB 2.0 compliant cable. Again, these ppl sell wireless routers that more than likely end up in giant strongly EMI/RFI polluted rooms so they know a thing or two about shielding and this $2 winner has always worked flawlessly IME(up to 24/192 of course).
The only fatal issues in the audioasylum guy's experiments are that:
1) All the pins of that Y cable are connected because it was initially designed to power USB devices straight off their routers(whose USB ports aren't powered at all), so you will have to break the +5V pin on the computer side: 
It really is dead simple(I used a cutter and a flat head screw driver in order to bend the evil pin and get it to fall off, you can experiment on other cables first). You can see on the second picture that I also pushed a tiny blob of blutack in order to remain 200% sure that no electrical contact would ever occur(the older I get the more I strive to keep Murphy's law at bay ^^)
And no need for an overpriced USB controller that would come with a +5V switch either, no pin = no problem

2) His DC cables are way too long! The shorter the better really in order to minimize interferences as much as possible. These aren't shielded and will act as antennas.
3) He used a bunch of $1 SMPS when obviously -as he concluded himself in his own thread- you'd have to dig up for a cleaner PSU and the Kingrex 5VDC MK2 PSU appeared as a weapon of choice to him for this purpose

I initially tried all those tricks with several other PSU's, such as this one(you can even see it in my head-fi trader feedback) and I would wholeheartedly agree with this quote:
something seems to have changed in the high frequencies... so much so
in fact that I may have to re-run my room correction measurements

The stock Y cable it came with was wayyyy too long, really really bright sounding and unbearably colored on the "Stello Eximus DP-1"(I wouldn't be surprised if it were silver based for that matter). So I knitted myself my own using a modded good ole copper "USB Injector" cable:
Pardo is using cheapo 2 pins round connectors that will more than likely oxidize to death, and even the PSU user manual it comes with advises to unplug and replug it several times in a row every few months as a precaution, huh. Kingrex overcame this issue by using a gold plated 3pins Neutrik XLR connection on their MK2 PSU, but more on this later =)

Most everyone in mid/high end audio will tell you that we are merely listening to the PSU, and even Pardo's website makes clear that the PSU is what colors the sound the most in his experience....hard to deny, as his PSU changed the sound drastically! Too bad deep bass appeared so colored, the SS felt like a stadium hall with barely anything in the center anymore and trebles were completely out of hand

So at this point, I also had the option of going with batteries but they come with their own issues:
1) the cheap ebay battery-based PSU's use nasty SMSP voltage regulators
2) most batteries have to be recharged every day or so, so you're SOL if you forget...or you have to buy two PSU's and reload one while using the other: headaches ahead.
3) these things will age rather quickly if you never turn off your DAC(as I do because I can't be hassled to wait for the darn thing to "warm up" in order to sound its best), and +1 year down the road these might not last that long anymore due to the constant loading cycles. Also, they tend to use relays that will make loud clicking noises at the end of their loading cycles and there is nothing I hate more than random relay clicks.
Luckily for us, the affordable 5V PSU consumer market bloomed in order to satisfy the Logitech SqueezeBox community, and the same "Kingrex MK2 PSU" name kept coming back on SB forums....many users agreed that it sounded really great on their SB rigs, that its markup wasn't stellar and that being 3A it could feed a whole bunch of USB storage devices plugged onto the SB.
There are many pro reviews that confirm that you get serious gear for your money, such as this one:
the Kingrex/Calyx combo proved to be something the Calyx alone always wanted to be!
Deep bass now has fundamental we never thought missing.  Subjectively, we felt that the low end extension extended down another octave or so.  It is also ironic when you have more infrasonic reach, you feel you have more "air" as well, even though the upper frequency range is more or less the same.  With air, you have a better sense of where the images are in the sound field.  Room ambiance are now better portrayed.  The soundstage becomes more three dimensional.  Slam and weight were also noticeably better with more visceral impact without muddying the mid-bass.  Calyx was a little short on pace and rhythm last we tested it, but now with the Kingrex PSU Mk2, the DAC can now really boogie.​

What's in the heavy black box:
Specs as follow:
Transformer: 48VA toroidal type

Voltage regulatory circuit: 5x2200uF at AC input stage
                                                3x4700uF at DC output stage
6N Furukawa PCOCC wiring
The nice thing about toroidal transformers is that they provide you with partial galvanic isolation from the mains, nothing to sneeze at. And the lighter the load, the lower the ripple hence the whole point of using an oversized 3A PSU.
Being able to output up to 3A also means that you could always use an extra Y cable and feed several pieces of equipment at once, or if you're lucky enough to have a DAC that feeds 5VDC(the "Calyx DAC 24/192" comes to mind) and runs a bus-powered USB controller, you could kill two birds with one stone as this 3A PSU would easily feed both simultaneously, and under a light load at that 
normal_smile .gif

I see that there are also SqueezeBox custom firmwares that allow async USB(with the M-DAC for instance), so you could use this 3A PSU to feed both the SB itself and the USB chip of your DAC =)
All this said, I was sold and decided to pull the trigger on this very promising 5VDC/3A PSU(£215 in the UK), soldered a Neutrik 3 pins gold plated XLR onto a pimped USB Injector and there ya go:
I like short DC cables and hard soldered connections, so it was only a matter of using a multimeter in order to find out which of the 2 wires on the PSU side of the "USB Injector" cable were GROUND and 5VCC, a bit of Cardas Eutectic Solder, a small piece of heatshrink later and we were in business

To make it perfectly clear, 6moons and Linnenberg Audio did confirm that the PSU ground and USB ground have to be shared.
The ground is not something we should be afraid of, as TI nailed down rather clearly writing a whole white paper about it(I'll update this review with the link later, as I don't currently have it handy).
My usual final test with a $10 USB dongle in order to ensure that its status LED would light up and that it's all good and won't fry my DP1:
It made more sense to me to plug a USB A/B adapter onto the device side of the "USB Injector" cable, together with a $5 Lacie 4ft USB extension cable to the computer:
Bang/bucks is huge on these Lacie cables IME and I do want to keep the PSU DC cable as short as possible, but you could also install the "USB Injector" cable on the host side and run a regular A/B USB cable to your audio device.
While you're at it, you may also wanna break the +5V pin on the computer side of the Lacie extension, I didn't try it myself yet but I keep it on the top of my "stuff to do when I'm bored" list ^^
There are also many Y USB cables, ranging from a grand to a few bucks(with a bit of DIY) so that could also be investigated.
So that's the Kingrex MK2 PSU with the pimped "USB Injector" cable and some $5 isolation feet(I was only glad to finally find a use to them
More pics of the PSU plugged onto my beloved DP1:
I should state that I use a rather good 400W Corsair PSU that was measured to output no more than 5.4mV ripple on its 5V rail under light load. The same review said that it was amongst the best at the time, and that was the very reason why I bought it. FWIR, latest PSU's are no better than this.
I should also make clear that the Stello U3 that is embedded into the "Eximus DP-1" takes care of the whole USB to I²S process, so basically the Kingrex PSU is being used for pretty much the whole digital side of the DP-1's USB input....hence the drastic SQ improvement that will have made all my efforts entirely worth it after all

So anyway, how does it sound then? Clearly not as utterly colored as the Pardo, but compared to the noisy computer power:
-deep bass is far more extended and a lot clearer, "less bloated" in two words
-SS has opened up rather drastically, but it's still entirely possible to play narrow mono(which wasn't possible at all on the Pardo IME)
-trebles and mids are much clearer and seem to be providing far more "resolution" to them. Mids are especially "thicker" sounding, which is most delightful on orthos.
-the sound is all around a lot more enjoyable, being less colored and far more refined....most delightful to listen to 

Going back to the computer power is a big no-no and this PSU upgrade turns the reference DP1 into something beyond words.....really. People who claim that a clean PSU makes all the difference in the world on transparent gear are very much spot-on to my ears. And I can hear why the 6moons owner tries his luck with every PSU and Y cable he can put his hands on ^^
As a conclusion, I can only confirm that feeding the U3/DP1 with a linear PSU is a one-way ticket and that there is no chance you will ever consider going back to the shared ATX computer PSU power afterwards

Also, the Kingrex MK2 PSU doesn't get warm at all(even if you leave it on 24/7 as I do) and it doesn't hum or makes any whining noise whatsoever.
Finally, I hope to have helped shed some lights on how to use a linear PSU for USB operation to those who wanted to know more, and I can safely advise to give this Kingrex PSU a shot because bang/bucks is stellar IMHO 

Jan 16, 2013 at 6:18 PM Post #2 of 41
nice review leeperry, i guess ill have to get this kingrex instead of aqvox, whenever ill find second hand u3 or ap2 for my w4s dac2 :)
lets just hope there is good quality ready made cable to this setup as well. dont like to make it myself ,specially with that many adapters.
Jan 16, 2013 at 7:14 PM Post #3 of 41
Glad you liked it! Well, I just found this one, but I don't think it would do what we want(even w/ its 5V pin broken):
I also forgot to mention that the Pardo PSU was outputting 5.5V, which is out of the 5% ATX tolerances......Pardo told me that it would fall within specs under load, but tbh I really don't expect a $400 3A linear PSU to suffer from any Vdrop under a <0.5A load(more likely 0.3A like the Hiface2). The Kingrex outputs a dead-on 5.00V 
normal_smile .gif

Well, Kingrex also make a Y cable but it's some point I thought about soldering a male B plug onto the "USB Injector" but SQ is great as is, I spent enough time on that USB PSU stuff already and I'm extremely happy with the results

Jan 16, 2013 at 8:16 PM Post #5 of 41
I'm sure you could find someone to make you a nice Y cable to the MK2 PSU, but soldering USB stuff isn't nearly as easy as it seems as there are mandatory requirements to impedance, shielding, bandwidth and you can imagine, I first tried my luck soldering a very short DC cable onto the B plug of a 4ft A/B Lacie cable but SQ was horrid: no bass and very shrill trebles 

The untouched Lacie cables sound great IME and that "USB Injector" does too so why bother really. I checked the official USB white papers and they make very clear that you MUST respect a 90Ω impedance and that a proper shielding is crucial for proper 480MBit/s operation.
Jan 16, 2013 at 10:05 PM Post #7 of 41
Leeperry, is it very complicated to solder u3 its own separate power in plug, so you would'nt have to use any adapters, plug in usb cable directly, cut out its power pins and connect kingrex to soldered power in plug... ?
Jan 16, 2013 at 10:08 PM Post #8 of 41
Well, it would void the warranty of the U3 and if you wanna avoid all soldering and adapters the best option is to have a pro making you a custom Y cable to the MK2.
Jan 23, 2013 at 7:19 PM Post #9 of 41
BTW, here's for an interesting link:
It really surprised me that the power source actually made this much difference

Pardo is dead on the money when he says that the PSU is what colors the sound the most, and headphones are the perfect candidates to hear this kind of differences IMO.
Jan 24, 2013 at 4:43 AM Post #11 of 41
So with these linear PS's on the market, this Kingrex included, is there any point at all to have anything but a regular plain jane ATX PS in the case or do you still recommend going with something like a Seasonic PS AND this Kingrex or other good linear PS?

Jan 24, 2013 at 8:19 AM Post #12 of 41
Well, the rabbit hole is endless you know

Jokes aside, a good ATX PSU will increase the life expectancy of your computer components. I posted a review of my 400W Corsair where it was said to give stellar ripple measurements but it seems rather clear that they received a golden sample from the manufacturer....anyway, it's a dubious story but the PSU's that were sold IRL didn't use the same oversized caps as in their review apparently.
This german site really didn't find my Corsair CX400 to their taste, prefering the most pricey Enermax.
And don't overlook the mobo either but even $10 USB3 boards now provide a molex connector on their PCB, OTOH God knows whether it will also be used to power the board itself...and obviously, the cleaner the power to feed the USB board, the cleaner the USB signal. If you plan on going bananas about your USB audio device, it's also a good idea to feed a clean PSU to the USB host side IMO. A cleaner PSU always pays in cash SQ-wise IME...many ppl always have beautiful stories about USB that "it either works or it doesn't" or the usual "it's a bunch of zeros and ones", yada yada.....but like every kind of high speed digital signal it comes with challenging issues. Chew the job of the Tx/Rx chips by using short shielded cables and feed them a clean PSU, you won't regret it =)
Jan 24, 2013 at 10:27 PM Post #13 of 41
Thanks again for the post up on the Kingrex.  I'm curious just how much computer "noise" is over or underrated.  I can understand the USB side of things and can see how the soundcard side of things could present some issues.  In the end, however, seeing that we have loads of computer based "solutions" and we do not exactly have universal support/agreement about one thing or another, it goes to show that in the end the subjectivity of it all will indeed remain.  But I like devices like this Kingrex, though it's very pricey is my only issue with it.  Seems like one can build something similar diy for $50-$100 max.
Jan 24, 2013 at 10:57 PM Post #14 of 41
DIY is always cheaper but 1) any error with PSU's connected to the mains can end up *very* badly(electrocution, magic smoke) 2) you pay for RMA, R&D, past prototypes, CE certification and a nice enclosure. You don't become an EE overnight basically but if you have the knowledge, time and patience to build your own then knock yourself out. I'm happy with messing around with 5VDC cables, not 230V PSU's.
If you count your time, the gear you will need to assemble it and especially test it(oscilloscope, etc), the possibility that you might possibly fail, kill something or that your homemade PSU might not sound that good after all....then the bang/bucks ratio of DIY won't be all that great 

And the beautiful thing is that you get a cooling-off period of 1/2 weeks depending on the reseller, so you try it and send it back if you didn't like it(at the expense of shipping costs).

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