My Gakken Diary, Part Two: Mechanics

Last night, after putting this thing together, and making a few preliminary experiments, I began to wonder if I had broken it somehow, because a few things did not make sense, at least not based on my assumptions of how a synth should work.

So I spent some time squinting at the schematics in the magazine, looking at the various videos online, and reading posts on Analog Haven via Nabble, and I came to the conclusion that the design of the Gakken SX-150 has some unique points.

Here's how I put it all together, based on my years of doing subtractive synthesis on and Arp Odyssey:

• The LFO Rate only affects the pitch of the VCO. You can't also assign it to the VCF. So it goes.
• This is the weird one. The VCF appears on some level to be a combo VCF and VCA.
• The above assumption is borne out by the fact that, at first, when I cranked the Cutoff on the VCF all the way to the right (or anywhere past about 2 o'clock), I couldn't get the Attack and Decay (AD) in the EG to have any effect when using the stylus. My original assumption about this synth was that the EG would be invoked when you touched the stylus to the carbon strip. But with cutoff anywhere above 2 o'clock, touch the stylus and its note on/note off. No shaping from the EG. It wasn't until I turned the Cutoff down to about halfway (below 1 o'clock) that this would happen. So that's where I get my theory that the VCF is sort of a combo VCF and VCA.
• Pitch Env takes the settings from AD on the EG and applies them to the VCO. If you combine Pitch Env with the LFO, you can get some interesting Frequency Modulation effects on the VCO.

I'm posting this in the hopes that someone else comes along, reads this, and either agrees with me or points out where my thinking is wrong.