[sdiy] Completed PE Minisonic2

[Julian Bunn]

I posted a couple of weeks back about my project to build the Practical 
Electronics Minisonic2 synthesizer. Well, last night I finally put everything 
in the cabinet I made, and the instrument is complete!

You can see a photo of it here:
http://pcbunn.cacr.caltech.edu/jjb/synthesizers/minisonic2/minisonic2_complete6.gif

and the full construction details, including my trials and tribulations,
are described on the web page:
http://pcbunn.cacr.caltech.edu/jjb/synthesizers/Minisonic2/

It certainly is capable of making some weird and wonderful sounds (I need
to make some MP3s and link them up).

The design features two VCOs, a Ring Modulator, a VCF (ladder-based), a Noise
Generator, VCO sync and intermodulation, twin envelope shapers, envelope
inverter, portamento, span and keyboard tuning. The VCO law is 500mV per
octave.

I've not tackled a project like this before, and I learned a few lessons:

1) The PSU is absolutely critical. I made the mistake of not building the
PSU specified, thinking I could make do with a 15-0-15 supply I already
had with some dropping resistors and zeners to get the 9-0-9 and 6-0-6
rails I needed. Although this works, it's too sensitive to load, and the
slightest variation in supply voltage alters the VCO frequency. Aarrgh.

2) Isolating the keyboard wiring sufficiently well so that there is no
drift is challenging.

3) I think that, while the switching feature of the Minisonic2 is very
convenient, I would prefer the full flexibility of a patch panel or cable 
system.


Julian