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Dave's CA BLOG

Moving on: An inexpensive ($20), but high quality, LPSU for my Regen cascade (warning: some DIY):

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After recently finding a (used) UpTone Audio MMK kit for a very nice price, I now needed a good LPSU for my Regen cascade, so the existing supply could be removed and used for my Mac Mini (as originally intended). I didn't want to wait for the up-coming UpTone "whatever-it-is" regulator. But the idea of a separate regulator module and a cheap raw supply sounded like a very good idea, so I looked around to see what I could find to combine it with parts I have hanging around and a little sweat equity to produce a much better then average LPSU for very little money :)

I found a nice looking regulator on eBay for $19 and ordered one. Next, rummaging through a box of old wall warts, I found one that had a transformer (not a switcher) and supplied 13vdc at .825A (close enough !). Some more rummaging in different junk boxes produced an old AKG cartridge box that fit over the regulator module quite nicely (with a little cutting and drilling). The module sat easily on top of the wall wart, but I worried a bit about the magnetic flux from the transformer being a little too close to the regulator electronics. Back to my 'junk' boxes for a steel bracket (again a little cutting and fitting and some paint). I also wrapped the transformer with some copper sheet. Last, but not least, a pair of wires salvaged from an old Kimber speaker cable, and a barrel connector bought off eBay. The design evolved into a stack of parts, which I found elegant and attractive (if not totally efficient, ie magnetic fields).


Construction details (from bottom to top):

Wall wart transformer: RS Optimus (China) #16-131, 13.5vdc, 850ma, 12W. (I don't remember what it originally powered) Opened the plastic case by freezing and then chisel thwacks along the seam (fun :).

Low V AC connection: Removed the DC circuit board and soldered the internal output wires directly to the transformer output (since the reg. modules rectifier diodes are so much better quality). Cut the external output wire pair short, stripped and tinned the ends which get clamped into the AC Input terminals on the module, through a ferrite bead (thanks to a friend).

Magnetic/electrical isolation: I smoothed the top of the transformer a bit with a file, and covered it with a little oversize piece of packing tape, then wrapped .010" copper sheet (K&S) around the top and sides of the transformer, to fit inside the wart case. Trimmed and painted a .100" thick steel 'L' bracket (from the junk box) and ACC'ed it to the outside of the wart case wrapped around the back. Both of these are cheap attempts to attenuate and shunt the transformers external magnetic field, since the circuit board plane is not very far above it.
The bottom of the reg. module is covered with 2 layers of foam tape to smooth and insulate the lands and solder/lead bumps of the printed circuit board. I left the outside protective layer of the tape on, so as not to stick the module to the top of the transformer case (actually the steel bracket).

Note: A 3/4" thick (or larger) piece of wood could easily replace my 2 magnetic shields. Sandwiched between the wart case and reg. module, the extra height of the wood would help isolation, but probably look ugly. I wanted a lower profile, and classier look :)
Or, find some kind of box for all the parts, but that has other problems to solve.

Regulator module: Model A270V2, Ultra-Low Noise (<40μV), Adjustable Voltage Regulator Module, 1.25~20V, 1.5A
eBay listings: Specs:

Based on Linear LT1963 regulator IC
1.6mm thick FR-4 fiber glass PCB (double layer).

HER303 high efficiency rectifier diodes for AC input.
RUBYCON YXF 1000uF/35V input/output filter capacitors, and metal film capacitors.

HQ terminal blocks for easy connection to in/out wires. 


Reg. case (optional): Clear acrylic cube from old AKG cartridge packaging (I just happened to have a couple hanging around :), with slots and holes cut for fit, ventilation, and adjustment. I very much like the look, much more in fact, then the physical protection it affords :)

Power cable: Twisted two Kimber wires salvaged from old 8TC cable, to a length of 30", then soldered onto a new 5mm x 2.1mm barrel connector. Stripped and tinned the other wire ends, and clamped them into the modules output terminals. A small cable tie around the terminal block provides strain relief. (note: I like to clean all flux and crap from my solder connections with lacquer thinner)


Stacked the wall wart, reg. module, and plastic case on top of each other and secured with a long cable tie, for a quick, easy and flexible assembly/disassembly. Wired up everything, and tested the output of the complete LPSU, adjusted it to 9.00 volts, and plugged it into a power strip (with no load) to burn in the electronics. After half a week it has only drifted .04v !

So, for a cash outlay of only $20, the regulator module and barrel connector, and some very fun time finding and assembling the rest of the (free) parts, I now have a fine little LPSU for my Regen cascade ! If it works out, I might take it over to a friends house to get some measurements. I will report back here once I have found the time and proper mood to do some careful listening around the change over of the 2 PSUs.


Pictures:

1 - Wall wart case and magnetic shielding parts
2 - All LPSU parts before assembly
3 - LPSU assembled, side view
4 - LPSU assembled, wire side

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Comments

  1. Hailey's Avatar
    Terrific stuff. So how has it been working for you? How does it sound? Did you get any measurements?
  2. Daudio's Avatar
    Ok, long past time to report on listening impressions for this little PSU…

    Since I was simply replacing one high quality LPSU (12v, 4A) with another (7v, .8A), not a lot of SQ change, if any, was expected. But…

    I heard what sounded like an increase in dynamic range, more then just a little bit, and, perhaps a slight decrease in soundstage space, through that was too subtle to be sure. Perhaps my powering the Regen with 12v, even with the additional heatsinks, stressed it out some, through I can’t see any mechanism to affect DR in this case ? Most (all?) of the SQ effects I hear in USB connection components (and server upgrades) fall into the ‘veil lifting’ category, at least to my ears.

    This little PSU sits up at the far end of my digital stuff power strip (API w/ 89db RFI filters), and has been so well behaved, I barely notice it, except for the nice light green LED that glows up through the clear acrylic case.

    Sorry, still no measurements. I just don’t want to remove it long enough to get it to a friends lab bench :)

    Dave

    P.S. All of my DIY solder connections are cleaned with laquer thinner, and all non-solder connections are treated with Cramolin contact enhancer (audio, video and computer).