Re: Doepfer in KEYs on filters

From Ricard Wolf
Sent Thu, Sep 19th 1996, 20:51

On Thu, 19 Sep 1996, Haible_Juergen#Tel2743 wrote:

> There is a statement by Mr. Doepfer printed, where he claims
> that there is no real difference between a Minimoog filter and
> a TB-303 filter, at least no more than component tolerances!
> 
> To "proove" this, they show details of both, the Minimoog
> and the TB-303 schematics - closeups of the filter circuits.
> ...

(Hi Juergen!)

I don't know if this has been discussed to death before, but I think
the _major_ reason for the "Moog" sound is the actual ladder design with
"diode-junction-based" controlled impedance element. I'm not saying that
the 'Mini and the '303 sound the same (and I don't really know exactly
what KEYs have messed up - I'm just using this as a starting point for 
discussion...maybe they were misquoting Doepfer, or he was really 
comparing a VCS-3 and '303 ???).

My guess is something along the line of that the nonlinearity of the
diode junction creates a slight bit of distorsion to create the 
"organic, airy" Moog sound. I love it personally - I borrowed a '303
a while ago and really loved the sound. Not worth what their asking these
days but I liked the sound, it gave me similar feel to other Moog (or
rather Moogish) designs.

Other instruments that have similar designs are:

* Korg Polysix and Mono-Poly, using the SSM 2044 chip, which internally
  uses a Moog ladder. Early Prophets used SSM chips, though I don't know
  if it was the 2044 or 2040.
* EMS VCS-3 - uses diodes instead of transistors connected as diodes.
* Practical Electronics' Minisonic.
* others...?

A question of detail is what the difference is between transistors and 
diodes...I won't try to go into that...

/Ricard
--
Ricard Wolf (mj20279@janus.swipnet.se)

Analog synth, railroad and Citroen fanatic