Fw: To use CEM or not.

[jhaible]

----- Original Message -----
From: jhaible <jhaible at debitel.net>
To: <synth-diy at mailhost.bpa.nl>; James Shearer <Jim at base.demon.co.uk>
Sent: Saturday, September 25, 1999 10:19 PM
Subject: Re: To use CEM or not.


> >  Hi, I looked at this and remembered an old filter kit I have tucked
> > away. I dug it out, and found it is based around an SSM2044 chip. How
> > does this compare to the SSM2040 ? or, for that matter, the 3320. One of
> > these days, I'm going to build this kit :)
>
> > James Shearer
>
> Let's go thru it from decent to better to best:
>
> The CEM3320 is a very good *linear* VCF chip. That is, it does
> excellent low distortion, low noise filtering. No more and no less.
>
> The SSM2044 is quite similar to the Moog ladder, but it's a folded
> cascade (current mirrors instead of common base stages). Distortion
> comes from the interaction of nonlinear pn junctions for VC resistors
> and linear capacitors, and from the differential input stage.
> This is a very "musical" VCF, not identical to the Moog, but
> similar in behaviour. Nice with slight overdrive.
>
> The SSM2040 is the "Queen of filter chips". Being an OTA filter,
> the circuit topology is very different from the Moog filter, but it
> also shows the interaction of nonlinear resistive and linear
> capacitive elements that come into play at decent overdrive.
> In addition to that - and that makes it unique - there is a second
> mechanism of overdrive caused by the OTA output's limited
> voltage swing, which results in very complex dynamic behaviour
> when the filter is *heavily* overdriven.
>
> As with all chips, the circuit that uses them has a big influence
> on the sound as well, so it's not *only* a certain chip that
> makes a difference. I know at least one instrument that used
> a 2040 and did sound outright ugly. (No, I won't tell which one.)
>
> JH.
>
>