Thursday, 19 August 2010

MFOS SoundLab Mini-Synth PLUS

The first Synth DIY project that I more or less successfully completed was a SoundLab Mini-Synth PLUS from Ray Wilson's site Music From Outer Space. I decided to purchase the necessary PCBs after having researched other options, in particular the Simplesizer project on a German Synth DIY site. Unfortunately, that project was abandoned a few years ago, and PCBs are not available anymore.

While waiting for the PCB to arrive and checking various suppliers for the necessary electronic parts I found out about an enhancement to the original design (the actual "PLUS" part). The PLUS enhancements carried the warning that they'll involve several kludges on the board and therefore require having some additional skills that I quite probably lacked. I boldly went for it anyway.

Building it was time consuming because I needed to learn basic skills such as soldering "on the spot" (both figuratively and literally). The desoldering pump was in frequent use. Also, I couldn't quite decide on the cabinet for the synthesizer which slowed things down for a while. Furthermore, I wanted a different panel layout than the one suggested by Ray Wilson. This required that I modified the wiring layout (i.e. the connections between the various controls on the panel).

When I turned on the Mini-Synth for the first time, it appeared to work! Mostly, anyway. The second VCO was silent. That spelled trouble in capital letters. I had no equipment to speak of, and was supposed to signal-trace and find a problem on a circuit that I basically didn't understand. To pinpoint the problem, I reasoned, it might be helpful to tune both VCOs to about the same frequency so I could check each of the circuits and compare the corresponding voltages (I had one functioning VCO to compare the malfunctioning one with). It took me a lot of studying circuit diagrams and a night's sleep to eventually notice that the same wire cannot have 0 volts at one and 7 volts at the other end. A close inspection with a looking glass revealed a dodgy soldering joint at a transistor.

After having fixed that, the SoundLab worked perfectly. I hadn't calibrated it to a proper Volt/octave scale yet. Nonetheless, turning knobs and throwing switches and listening to the noises that it produced was a lot of fun. Most importantly, though, I was hooked.

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