Boss CS-2 Compression Sustainer...

[Jeast78]

Has anyone tried to build one? Is it possible?

[R O Tiree]

If you can get hold of the OTA chip, then yes it is possible. That's the trick, though...

[gritz]

I would imagine that the main stumbling block would be in trying to source the BA662a vca chip for sensible money. They are in demand by fans of Roland synths (like the TB-303 and Jupiter) and I expect that a lot of CS-2 pedals have been culled for these chips. I understand that the BA6110 can be used as a replacement - although I don't know what (if any) circuit mods would be required. The BA6110 doesn't have the "mojo" connotations, so it would likely be a bit easier to find, with the caveat that ebay is always a crapshoot.  

Apart from that, it's a pretty standard vca feedback compressor in vaguely the same vein as the Dynacomp, so I don't forsee any barriers to getting one to work.

Hope this helps.

Edit: R O Tiree beat me to the flag...

[Jeast78]

Apart from that, it's a pretty standard vca feedback compressor in vaguely the same vein as the Dynacomp.

Which would be the other option...

[Mark Hammer]

The BA662 is a proprietary chip, made for Roland, which means you will not be able to find it through any standard distributor, though I imagine there's gotta be at least a few vendors in the Akihabara ( https://en.wikipedia.org/wiki/Akihabara ) that have some.

Personally, I think much greater value is to be had by building either the Engineer's Thumb compressor or an SSM2166-based compressor.  The latter includes on-board noise reduction that solves the eternal complaint of compressor users: hiss that creeps in when you stop playing.