[sdiy] SEM filter questions

[David G Dixon]

> All you would need to do is get an old SEM module and trace 
> the schematic yourself.

No need; the schematic is public information.

> If there is patent protection, its expired... and copyright 
> only covers the actual factory schematic and the circuit board.

Patent protection?  Ha ha ha ha ha...

> Of course if you say the word "Oberheim" you are (probably) 
> infinging a registered trademark and you could be in a lot of 
> trouble. Likewise you might not be able to say "SEM" clone...

I was thinking of calling it the "Uberheist SOL filter".

I'm just kidding, of course.  I have no intention of marketing this.  If
anything, it'll be a one-off for a mate, and just the board at that.

> You could say "Inspired by the legendary "synthesizer 
> expansion module" of the early 70's that formed the heart of 
> some of the first and most respected polyphonic synthesizer 
> systems"...

How about "Inspired by some cheesy 80's rock solo..."?

> BTW I'm not super-impressed with the SEM filter overall, its 
> good but not special IMHO. I don't think the FETs add much 
> 'character'.  The most obvious thing that could affect the 
> sound is the resonance limiting circuit.

That's what I'm thinking too.

> The state variable filter is pretty much fair-game imho

I should hope so, since there are already about 30 of them on the market, in
every format imaginable.