Kevin’s Opto-Key build environment has transferred from Synthfool to This Old Synth. The components, software, circuit boards etc. arrived on Wednesday afternoon. Two days of work later I have partially completed 5 units. Time to get a components order submitted so I can complete them! I did purchase the very last of unit built by Kevin and have begun testing using it in my MiniMoog; exciting times!
As a tech I’m increasingly frustrated with the chore of trying to restore the (oxidized) key contacts on the MiniMoog to full operation, and unless it is frequently played the issue of “squirelly keys” comes back. I have been installing Opto-key for my customers which removes the key cleaning cycle, AND adds simple note-on/off MIDI.
I was concerned and saddened to hear that Kevin Lightner at Synthfool could not continue the Opto-key project as it addresses the biggest reliability/playability issue with the MiniMoog, and have negotiated with him to transfer ownership here.
Once the on-hand materials such as circuit cards arrive I will commence building the product to Kevin’s spec and make it available for sale.
As I’m also a software developer with experience in embedded systems I plan to enhance and support Opto-key moving forward. I’m really excited by this!
The MiniMoog, along with many vintage synths, suffers from oxidization of the key contacts. It needs all keys to be pressed regularly to break the building oxidization, before it becomes a problem. The symptoms of the keys going bad are they become “squirelly”, i.e. multi-triggering, or dead due to not triggering at all. Another issue you see on keyboards is that as the keyboard generates CV from a resistance chain (1volt/Octave being common), any resistance in the contact alters the voltage out, thus frequency.
The folks at www.synthfool.com came up with an optical method of detecting key presses, called the Opto-Key. This incorporates a micro-controller in the design, making it possible for them to also add MIDI In/Out. Jason, the owner of this early MiniMoog, decided that as it was in need of service, he would ask me to implement Opto-Key, rather than continue with the key contact clean regime.
The keyboard was re-bushed while disassembled for the upgrade, and I can report that it works nicely. A service was also carried out, and some pots had to be opened in order to clean them and banish crackles. For reliability the disintegrating C280 “Tropical Fish” capacitors were replaced, the power supply re-capped, re-greased, and bridge rectifier replaced. All switches and open-back pots were cleaned, and the unit set to spec. Plays nicely now.
This early unit (#242) needed some further work after another tech had worked on it. The keyboard had been re-bushed, but the bushing supports had not been straightened, which coupled with some badly stretched key return springs had left it unplayable. This was resolved, and once the set-up was completed (it had been tuned from C on the far left when in fact the first key is an F!) it played great (taking into account the temperature drift you get on a version 1 oscillator card!).
The owner of this unit was having trouble finding someone to repair its dead oscillator and other issues because it had a home-brew CV interface installed that was not working. He had taken it to another repairer who would only work on it if the mods were first removed, but would not take on the mod removal task. It therefore came to me for mod removal and repair, and thankfully I had another MiniMoog in that I could compare the mod and original wiring with. Continue reading