The Smallest 5-Pin Power Supply...

[sean]

The Smallest 5-Pin Power Supply sitting with the rest of the family.



In my moronical quest to build myself a power supply for my Janus preamp, I discovered that there are a bunch of tiny potted power supplies available, and some of them are affordably cheap.  I ordered one made by Delta, specifically, model AA04D1515A.  It is a 4-watt switching power supply with +15V and -15V outputs.  It is super tiny: only 1.44” by 1.06” by 0.67” tall.  The obvious challenge is to put it into a tiny little box.  The size of the XLR connector is more of a limiting factor than the size of this tiny power module.  I had a little Bud CU-473 box handy, so it had to be built.  The final result is quite tiny:




This is the shopping list to build a 5-pin power supply with the Delta AA04D1515A:
1 each  Power supply module, Delta AA04D1515A
1 each  Bud CU-473 cast aluminum EconoBox, 4.68" x 3.68", 1.34" tall
1 each  Panel-mount 5-pin XLR connector, like Switchcraft DE5F
2 each  Switchcraft 11 or L11 mono 1/4" jack
1 each  AC Power Switch, like TE/Alcoswitch TRD13D10WLLR204 (expensive), or CW GRB213B03BB (small, no LED), or the big round ones like CW GRB130A05BB2, Mountain 103-R13-135B-02R-EV, 103-R13-135A2-02-EV, 103-R13-135A-02-EV, or E-Switch RR3130ABLKBLKES
1 each  Fuse holder, Littelfuse 01500274Z.
1 each  Fuse, slow-blow, 2AG or 5mm x 20mm, like Littelfuse 218.500 (500mA, SB)
1 each  C14 power inlet connector, like Bulgin PX0580/28
1 each  C13 AC power cord stolen from your old computer
1 each 2KΩ to 10KΩ resistor to limit current in the power-on LED
1 each  Perfboard, like Vector 64P44WE or Keystone 3405, cut down to 2” x 2”
2 each  #4-40, 3/8” or 1/2” flat-head screws and nuts to mount the XLR connector
2 each  #6-32, 3/8” or 1/2” flat-head screws and nuts to mount the AC power inlet
4 each  #6-32, 3/4” or 1” flat-head screws and nuts to mount the circuit board
4 each  Nylon spacers to mount the circuit board, 1/4” tall, 3/8” diameter
1 each  Epoxy to insulate the AC power connections under the circuit board
Assorted wire, shrink tubing, solder, and tools from your basement or garage.


You could wind up spending more than $130.00 to assemble all the supplies and tools.

The items specifically in the shopping list will cost eighty bucks plus shipping from two suppliers (and a trip to the hardware store).  This assumes that you got the AC power cord for free, you got the DE5F from Markertek for cheap, and you bought the expensive switch with the LED.  You can save ten bucks if you get a cheap switch.  You should also buy a few bucks worth of heat-shrink tubing for insulating the connections at the AC power inlet, fuse holder, and the switch.

You will need two cans of spray paint: one can of primer and one can of topcoat color.  You will have to buy some tools - the step drill and de-burring tool most likely.  I assume you already have hookup wire and a soldering iron.  See the list of tools that you might need at http://ep-forum.com/smf/index.php?topic=9657.msg53396#msg53396.

Before you know it, you have spent more than one-hundred-and-thirty dollars, waited ages for shipping, and you haven’t even starting building the thing.  That’s why I recommend that you buy the finished 5-pin power supply from Vintage Vibe, RetroLinear, Avion Studios, CAE, or some other folks. 



The diagram below shows the wiring connections for a 5-pin power supply built with a Delta AA04D1515A power supply module.  This diagram shows it in a much larger box than the CU-473, so that the wiring connections are clearer (and easier to draw).




This drawing doesn’t show the switch having a power-on indicator LED.  If your switch has one, just hook it up between the positive supply and ground, and insert a resistor to limit the current through the LED.  I used a 10KΩ resistor, but you can use a smaller value if you want the LED to burn brighter.  This 10KΩ value works fine with the switch I used (Tyco/Alcoswitch TRD13D10WLLR204).  If you choose a switch that has an indicator light that is designed to run on the AC mains, then see one of the drawings from my previous efforts at building the perfect 5-pin power supply.  See the second drawing in this post:  http://ep-forum.com/smf/index.php?topic=9657.msg53394#msg53394


The drawing below shows the hole and component locations in a Bud CU-473 box:




You may notice that I fixed the orientation of the XLR connector with respect to the quarter-inch outs.  The XLR is now on the right side (closest to the piano).  To make space inside the box for mounting the power supply, I had to move the power switch around to the right side. 

Cutting the holes for the AC power inlet and the XLR connector is explained in my earlier work, so see http://ep-forum.com/smf/index.php?topic=9657.0 for more detail.  This time, I had a step drill with a 24mm stop, so the XLR hole was a simple process.

This time I made a much more sturdy jig for holding the Bud box while drilling.  The sides of the CU-473 Bud box seem to be at a 3° draft angle.  I taped a pair of paint stirrers to the bottom edge of a piece of plywood to create a bed angled at 6°.  So the top edge of the Bud box was level for drilling.  It looks like this:



The larger models of Bud Econoboxes have a different draft angle closer to 2°.  If you have a fancy drill press with a tilting table, you wouldn’t have any trouble.  My drill press does in fact have a table that can be tilted, but I don’t really want to experiment with removing the drift pin (in fear that I will never get the table to be tight and level again).

Audio connector holes drilled:


The hole for the AC power inlet: 


All the holes:



After drilling the holes and polishing or painting the box, you are ready to wire it up.

All the components ready to be installed:



The switch I used cost almost fourteen bucks, and I don’t think I would choose it again.  I bought this switch because it didn’t require a large mounting hole and had a power-on indicator LED.  However, the solder tabs are tiny, so I could not use 16AWG for the AC power mains.  I had to use 20AWG wire, and there was not much room to work.  After soldering the connections, I slopped a bit of epoxy over the terminals for permanent insulation.  I just noticed that the photo above shows the wrong 1/4" jacks.  I am cheap, so I buy Switchcraft 12B connectors in bulk.  When I need a mono jack, I simply break off the arm that would connect to the ring, and break off the terminal for that connection.  They break off cleanly.

Delta has surprisingly little documentation on their website to help with design considerations for their products.  I admit that I did not try to contact them directly, so all I had to work with is the spec sheet:  http://www.deltaww.com/filecenter/products/download/01/0102/datasheet/DS_AA04S_D.pdf.  There is no information about mounting it upside down, no creepage specs, and no example circuits.  It does say to use a 1A slow-blow fuse, but I have had good luck with a 500mA slow-blow fuse.  The inrush current hasn’t blown a fuse yet.  When testing the power supply module, I was not able to get it to heat up at all.  Switching power supplies are wonderfully efficient, and are famous for not creating a lot of waste heat.

The Delta module needs to be securely mounted to prevent any accidents with the AC power mains connections.  It is made to be soldered onto a customized printed circuit board, and the pin spacings are not convenient tenth-of-an-inch centers.  I decided to mount it on an epoxy and fiberglass perforated board, so I had to drill out some parts of the perfboard to allow the pins to go through.  The module is secured to the board by the solder connections, and four screws hold the board firmly to the chassis.

You can cut the glass-reinforced epoxy perfboard down to size with a hacksaw.  Grind, file, and sand the edges until they are smoth enough to make you happy.  The glass dust is not good for your eyes, nose, and lungs, so wear a dust mask and goggles.  Drill a screwhole at each corner of the board.  Mount the Delta power module to the perfboard by soldering wires to the terminals.  To insure absolute safety during construction and testing, mix up a little two-part epoxy, and coat the soldered connections on the bottom side of the board.  With the AC mains connections covered with a layer of epoxy, you won’t burn the house down (maybe).  The board holding the power module is screwed to the chassis bottom plate using nylon spacers.

The fuse holder is an annoying pain when it comes to stuffing it into the box.  You need enough loose wire to change the fuse without too much trouble.  I coiled up all the wire, and tucked it into the box, but I doubt that it will look very pretty if I ever have to pull it out and change the fuse.  I didn’t use any quick-disconnect terminals, because there is not enough space in the box.  There isn’t enough room to mount molex connectors on the perfboard either.


All the guts installed, ready to close up the box:



When finally put together, it looks really nice and remarkably small.  It fits in your pocket.

Here she is looking very thin next to her friends:


Now, at long last, I am done with this mess.

Sean

[AvionKeys]

This is awesome work! And such great detail in the description and drawings.
I looked up the power supply on mouser and it looks like it outputs about 133ma on each line. That might be a little underpowered.
Have you measured it under load?

We sell a pcb power supply in addition to the regular power supply / output box for the Janus and we moved up from 250ma to 500ma per leg. Mostly to ensure longevity.
Really it might not be an issue but you may want to check it with a thermal gun once it's been on for a bit.

Again, seriously amazing work. Do you have links for those other builds as well? 

[sean]

Hey Morgen!

Thanks for the kind words!

The link above at the top of the post labelled "moronical quest" leads to the writeup of the other five power supplies.  The writeup for the one built around your module starts at http://ep-forum.com/smf/index.php?topic=9657.msg53394#msg53394.

Of course I tested the Delta module under load.  Pretty soon after turning it on, it went from 68°F to 75°F exterior temperature.  After an hour running the Janus preamp, it was still only 77°F.  The temperature rise is essentially undetectable against my skin.  But since you asked about it, I will test it with higher-current loads.

There is little reason to supply more current than the Janus preamp needs.  The 5-knob version that I own drinks less than 40mA from each side of the supply, so the 133mA that the 4-Watt Delta unit can source is plenty.

Sean

[AvionKeys]

Cheers Sean!

Such awesome work. I don't know why I thought the Janus used more power than that.
Went back and looked at our notes and I think we had it a bit higher but yeah, totally fine.

I figured from your detailed post you load tested it, just wanted to make sure.

Super nice work.

[sean]

I did a little more formal temperature testing of the Delta Power Supply Module, model AA04D1515A.

I arranged a bunch of 10W resistors into four different pairs of loads (350Ω, 250Ω, 150Ω, and 116Ω).  I tested the module with both the positive side and negative side of the power supply connected to identical loads.  I measured the module's temperature with a Fluke 62mini infrared thermometer.  The ambient temperature for these tests was 67°F.  Informal empirical testing did not find any particular hot spots on the exterior of the Delta module, so the temperature was taken off the top surface of the module.     

I switched on the power, and measured the temperature every five minutes, and recorded the measurements below.  At the 40mA output needed to run the Rhodes Janus preamp, the temperature rise was minimal.  It rose to 79°F and stayed there.  This is just barely warm enough to detect by touch (it started out cold to the touch, and five minutes later felt "not cold anymore").  I stopped measuring after 90 minutes.  I think it is safe to say that it would run at that temperature indefinitely. 

These tests were performed in free air, so maybe the module would get slightly warmer when confined inside a small box.  The spec sheet says it can run at full capacity in an ambient temperature of 122°F (50°C).  The spec sheet also says the module itself will shut down at 194°F (90°C), but restart at 153°F (67°C) (I assume they mean internal temperature).  In my high-current tests, I got the module up to 101°F without any apparent problems.

So I think we should feel comfortable using this 4-watt module to power the Rhodes Janus preamp.

Here is the data for my four tests: 


Target  Load  Current
Current Ohms  Measured  Start    5min     10min    15min     20min     30min     60min     90min

 42mA   350Ω  42.9 mA   65 °F    73 °F    78 °F    78.5°F    79 °F     79 °F     80.5°F    79 °F

 60mA   250Ω  59.2 mA   70 °F    76 °F    80 °F    83.5°F    84.5°F    87 °F     gave up after 30min   

100mA   150Ω  99.5 mA   67.5°F   80.5°F   88 °F    90.5°F    93.5°F    95 °F        "   

129mA   116Ω  127.1mA   70 °F    86 °F    93 °F    95.5°F    98 °F     101 °F       "   


The 116Ω  loads proved that the module could easily produce the current claimed on the spec sheet.  The module got warm, but still comfortable to hold in your hand (barely more than body temp).  The load resistors, however, got impressively hot.  The 100Ω  resistor carrying all 129mA of current got up to 155°F - quite painful to play with. 

Sean   

[AvionKeys]

Sean!

Been away so I missed this follow up.
What dedication. I wish more people really load tested their stuff....but this was wonderfully thorough!
It wasn't even flinching at expected load so, again, my initial memory was off, it's clearly a solid choice.

Kudos mate! It's one thing to make a power supply. It's another to really test it! Just awesome.