Symetrix PS-3 Power Supply for Lucid AD9624 and DA9624

I have a few old Lucid DA 9624 digital-to-analog converters but none of the came with a power supply. A quick search online found that they use a Symetrix PS-3 power supply. Unfortunately I couldn’t find one for sale for less than $100! Pretty expensive for such an old device that I just want to test and sell.

I found a couple old forum threads discussing the power supply pinout. The only one that had a picture of the pin numbers is unavailable on its original website and can only be found here on the Wayback Machine.

It appears that the power supply outputs two AC voltages — one 8.5 VAC and one 37 VAC center-tapped. I decided to buy a couple transformers and build my own power supply — partly because it was cheaper that buying a proper supply and partly because I had been designing my own class-D audio amplifier for which I needed a moderately sized transformer anyway.

I bought both as toroidal transformers from Antek Inc. on eBay. The 8.5 VAC input was supplied by a 9V+9V AN-0209 rated for 25 VA. The 37 VAC input was supplied by a 18V+18V AS-1218 rated for 100 VA, however I got this particular size for later use in my amplifier project. The AN-0118 10 VA version would be perfectly sufficient since the Lucids only draw 250 mA from the 37 VAC input. These transformer voltages aren’t exact, but darn close and within tolerance.

Before I wired up and plugged anything into the Lucids, I wanted to be sure that the pinout was correct. I took one apart and examined the PCB traces. Sure enough, pins 1 and 6 feed a small full bridge rectifier that charges a single capacitor. Pins 3 and 7 feed into a larger rectifier that charges a pair of capacitors, with pin 2 being the center tap for neutral. Pins 4 and 5 are connected directly to the shielding pins and connect to chassis ground through a 10 Ω resistor and small capacitor in parallel. I sketched up the circuit diagram as well as the DIN-7 connector pinout.

DIY Symetrix PS-3 power supply schematic

With the schematic verified, all that was left was to actually wire it all up. I wasn’t trying to make a permanent PSU for these — I just needed something that worked to test my devices with. This is the mess I ended up with. You may notice that the larger transformer on the right has a violet wire coming out near the black and red primary wires. This violet wire is attached to the iron core and can be used for grounding it. I didn’t bother connecting it to anything.

Transformers wired up to DIN connector

Needless to say, it’s not something I’d use daily, but it worked! I wish I had taken a picture of one of the Lucids powered on and running, but I was too focused on actually testing them. Afterall, I’ve had them in a box waiting to be tested for a couple years.