[sdiy] Oberheim SEM module

[Magnus Danielson]

From: jbv <jbv.silences at club-internet.fr>
Subject: [sdiy] Oberheim SEM module
Date: Tue, 06 Apr 2004 12:47:37 +0200
Message-ID: <40728AC6.D2331D55 at Club-Internet.fr>

> Hi there,

Dear JB,

> An old friend of mine (with a solid background
> as a hobbyist in electronics, but who unfortunately
> can't speak english very well and therefore isn't
> on this list) has just decided to kill time by building
> some old commercial analog gear from schematics.
> And he'd like to start with the Oberheim SEM module,
> as we found sources for almost all the parts.

Cool.

> Before starting, he'd like to know if anyone has a
> previous experience on such an undertaking, and if
> advices / tips / suggestions could be provided through
> this list, mostly about traps to avoid, possible mods &
> improvements (like modifying the filter from 12dB/oct
> to 24 dB/oct, or changing the ADR into ADSR...).

Well, I'm not sure the SEM is the first thing to clone, but if you feel like
it, by all means go ahead and report what you learn. As for myself, I've
repaired SEMs and also owns them. Also, if you look at my ASM-1 webpage you'l
see that the ASM-1 is nothing but a modern SEM to a high degree, even if
certain choices are done by other means.

What could be viewed as a flaw in the SEMs is the lack of full ADSR. I would
also opt for more waveforms. The filter of the SEM has some interesting
features, so you might want to keep that, but if you are not religous about it
why don't you add a 24 dB/Oct filter while you are at it. The SEM is semi-open,
but it's not too badly tied up.

The oscillators have a little different design than we do it today, but then
part of the character may very well be in that design.

> Last but not least, what's the best source for the 1K Tc ?

Beats me. I got mine from Paul Schrieber some time back. Don't know if he is
still at it.

Cheers,
Magnus