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.
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.
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.
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.
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.
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.