Split-rail power supply

Building an adjustable split-rail power supply

Posted by revmecha on September 18, 2015

After building a few attenuators to use with Mutable Instruments Peaks, I decided I wanted to build a basic buffered mult with trim pots on the outputs. I thought about mixing the signals but decided to normal one of the outputs so i could either use one signal four ways or use two signals two ways.

Breadboarding the Circuit

I followed a couple of simple schematics and landed on a combination of the two with an added indicator LED. The Peaks has a wide PPV and I like being able to reuse the modulated signal while being able to turn it down for more subtle modulation. I initially was going to have an LED to represent each channel but then decided on using an indicator to show a mix of the output. I had green to represent positive and blue to represent a negative signal. This didn't last in the final build.

Testing a LED driven by a transistor to indicate voltage.

Building the Boards and Panel

Of course it would have been nice to make a nice etched PCB but I decided to just build and wire it up with what I had on hand. The next one I build will have more features and use an etched circuit board instead. Using perfboard and solid core wire made it easier to plan out but also made space very limited.

Gluing down the wiring paths on both panels.

I started with a template of the front panel and used that to map out the paths. I didn't want to cut the potentiometer knobs so I ended up making two boards and extended the knobs through them to the front panel.

Finishing the Front Panel

I finished drilling out the front panel plate once I had the boards completed. I left the clear plastic on the metal plate to protect from scratches while I finished the build. Everything fit very tight and I learned some valuable about planning board layouts for the future.

Module with holes drilled and knobs installed.

I didn't photograph installing the LED. It was really hard to make the rectangular LED fit and cut a perfectly sized slot. I got frustrated and decided to just use the one LED for a signal indicator. I'll probably just use the round LEDs for the next one.

Testing and Debugging

I finally got the module completed and installed in my case. I thought I had tested everything but quickly realized there was a grounding problem. I had tested all throughout the build so it was really frustrating to get so far and have it not work. I took it apart and was able to fix the ground problem (I still don't know how I missed it) and get it assembled again without breaking anything.

Completed module showing the perf boards and power socket.

Final Installation

Finally I got it finished, added some labels, and mounted it in the case. It actually turned out better than I hoped and it has become a module I always use. It's next to a more standard mult/mixer in the picture and it's really made me want to make another one with a third channel.

Module in the case with some basic labels.

These modules are pretty common and fall under different names and configurations. I'm sure it would be nice to have CV control but I'm happy having a mixer/mult I can adjust. I also have VCAs and Attenuverters and they each serve a purpose.