ESM-2: new single board Japanese synth

[Ricko]

I see on the Radio Junkbox website they have been designing a new single board synth. It looks a little more like a MFOS rather than an ASM-2. dual 555 based VCOs and Moog VCF/VCA. Most interesting thing about it is that it has a built in MIDI-CV controller.

The schematics are here
http://www.rjblog.net/esm-2/ESM-2_PCB_DIAGRAM_20090927.pdf

You can get a Japlish translation (pretty usable, actually) from here:
http://translate.google.com/translate?js=y&prev=_t&hl=en&ie=UTF-8&u=http%3A%2F%2Fwww.rjblog.net%2Fesm-2%2F&sl=ja&tl=en

It looks like it is still under development, and they are looking at little cases to fit it in. I didn't see any links to suppliers or anything like that, but there is a kit of parts. To get to the links, better to jump from the original page
http://www.rjblog.net/esm-2/

[joshco]

The Schematics as well as Demo Sounds are quite nice.
The Midi Controller looks nice. Cv Gate, ADSR, LFO, Modwheel.
A Midi clockable CV Controller is quite rare...

[Sine]

555 VCO's ?

I wonder how well those track ...

[Ricko]

The comments that people write about the Fatman concentrate on their tendency of 555s to synch more than linearity. They prefer 7555 or the "Lee diode modification" with extra power-supply decoupling.

I suppose the linearity could be improved in hardware, but since the KCV is generated by the built-in MPU, the conversion tables could be adjusted in software, if that were important. I don't know why it generates 1V/8ve anyway, it would be more stable to generate exponential response voltage directly, I would have thought.

[alcofribas]

The VCF is more Synthi-like than Moog-like... personally I like this. And it looks like a really clean design.

The VCA has exponential response so the sotfware EG will generate linear envelopes. This makes for slightly delayed notes on slow attacks and some people don't like this. Wow, all envelope parameters are voltage controlled! Too bad there's only one of these. Perhaps two less sophisticated EGs would be a better use of resources.

There's a lot of hand-matching of transistors to be done here. Or maybe they don't care.

All in all an interesting design. And they'll provide the microcontroller program so you won't have to write it!

[thundarr]