[sdiy] SEM filter questions

[Magnus Danielson]

On 04/19/2012 04:02 PM, Neil Johnson wrote:
> Hi David,
>
>> A buddy has asked me to build an Oberheim SEM-inspired filter.
>
> I guess if its just for personal use this would be OK, but for
> commercial use I'd be a little careful now that Tom is back in the
> game:
>
> http://www.tomoberheim.com/
>
>> I've been
>> looking at a schematic I found on the web for something called "SEM-1A"
>> which looks to me like a garden-variety SVF built around CA3080 OTAs and
>> caps with 2N4302 JFET buffers.
>
> Yep.
>
>> Is this "the" SEM filter?  I was under the impression that it was based on a
>> CEM chip.
>
> Nah.  While Oberheim did use some CEM and/or SSM chips for things like
> ADSRs and so on the filters were 2-pole SVFs based on CA3080s.

Oh really? For what synth are you talking about? It really changes over 
the years.

SEMs use really standard stuff. The CA3080 is as special as it gets.

OB-X is really SEM like filters, but when you get to OB-8 it is all 
modernized.

One thing which is special about the Oberheim SEM is the low-pass to 
high-pass panning. I think only the ARP 2500 had it prior to that. It is 
really lovely to create some character sounds IMHO.

Cheers,
Magnus