MOTM

> >wait and first hear the upcoming SEM filter. Like the ARP, it is a
> typical,cheesy state-variable filter with "bad" op amps (LM741s,
> etc).<
>
> I'm sorry, did you say 741's?
>
> Doesn't this go against the MOTM "CD quality" philosophy?  There is
> no way a filter based on 741's etc. is going to be quiet. If you are
> going to go that route, I have a 741 phaser design you'll just
> love. :-)


Hi John,

Yes of course there's a 741 inside, and it's crucial for the sound.

My philosophy of making circuits "as good as possible" when I
contribute them to MOTM can mean entirely different things:

For the "universal" 4pole LPF (M-440) the goal was to have
lowest noise, lowest CV feedthru, clean self oscillation over
the whole range, etc. (And some of the SSM2040-typical
side effects, too, which belong into the next category.)

For a "specialized" 4pole LPF like the M-490 (early-Moog
style VCF), the goal was to come as close to that Moog
Modular VCF as the "uVCF" concept allows. This means
*no* self oscillation at low frequencies, and even more,
this means an acurate emulation of the harmonic distortion
vs. frequency under all conditions.

These are very different design goals, and it was fun to
work on both of them, as different as they are.

The upcoming SEM-style State Variable Filter belongs
in to the second category for sure. (It will have a few
extras above the original, but I won't tell before Paul
officially announces this.) This 741 is part of the sound,
and even more, in that particular circuit it's used to
_compensate_ some unwanted effects that would
otherwise be caused in other parts of the circuit.

These old designers of now-vintage circuits -
Moog, Oberheim, and all the others - have been
very clever to make the best of the components
they had at the time. If we want to emulate such
circuits today, we have more choices, but
it needs a lot of analysing to decide where a
"modern" component will bring improovement
without negative side effects, and where just
using the "vintage components" is the best
thing you can do. There is no general answer
for this - it depends on the circuit.

JH.