303 filter

[Fraser, Colin J]

> -----Original Message-----
> From: jhaible [mailto:jhaible at metronet.de]
> Sent: 02 November 1998 20:19
> To: schmitz at patho.bonn.com
> Cc: DIY; fa_diy at fa.camelot.de
> Subject: 
> 
> 
> The transistors are connected as diodes. So, unlike
> the Moog ladder, you don't have buffer stages between 
> the individual RC filter stages. Each stage is loaded
> by the following stage. So in the  interesting region above
> the cutoff frequency it has a slope of (approximately) 
> 18dB/Oct. The wording "18dB" appears  in the  service 
> manual of the EMS VCS3 / Synthi A (which also uses a 
> 4-pole diode ladder filter) and it describes the typical 
> behaviour of this kind of filter fairly well. It's quite
> different from a Moog filter not only in topology, but also
> in sound. That's all there is about it.

Is it just the change in slope that alters the sound ?

If so, would it be possible to constuct a filter with independant control
over each pole (eg an OTA intergrator stage), and derive the control for
each pole from the main control to provide different filter characteristics
?

Or are there other differences ?


Colin f