Thanks Crow for the excellent details.
Let me see of I got it:
The freq and res pots affect their respective parameters by 0 to 80%.
The 1V/Oct and Res inputs affect both filters respective parameters by 0 to
20%.
One other thing, what is the useable input voltage ranges for the Res In and
1V/Oct In jacks?
George
----- Original Message -----
From: The Old Crow <oldcrow@...>
To: motm group <motm@yahoogroups.com>
Sent: Saturday, July 13, 2002 4:33 PM
Subject: Re: [motm] MOTM-480 resonance
> On Fri, 12 Jul 2002 groovyshaman@... wrote:
>
> > I just finished listening to the MOTM-480 sound bites - wow! (I know, a
> > week late and a dollar short.) Lots of nice resonance, nearly
self-osc. I
> > know Paul has indicated this module will not self-oscillate, but it
sounds
> > nearly there. I've never had the chance to play with a CS-80, alas, but
I
> > have read that its filter does not self-osc. So I'm wondering, does the
480
> > closely match the resonance capability of the CS-80, or are we getting
more
> > res for "free"?
>
> The filters can't resonate as they have feedback limiting components in
> the circuit specifically to prevent oscillation. I suppose one could
> build the circuit board without the six feedback limiting networks around
> the six 'cells' (four filter stages, two resonance control stages).
> Someone once asked if a "self-osc/non-self-osc" switchable mode could be
> done: in theory it is possible, but in practice it would be cumbersome as
> all six networks would have to be disconnected, and the resulting extra
> circuit traces to cell nodes from analog switches might start to affect
> the response.
>
> Since the actual CS-80 filter circuits are linear CV response and MOTM
> is exponential response, changes were made to the CV front end so as to
> provide expo response for the frequencies and resonances. On a
> CS-50/60/80, there are separate frequency and resonance controls for the
> high-pass and low-pass filters. There are also "global" frequency (called
> 'brightness' on a CS instrument) and resonance controls on the CS
> machines. These are provided for on the MOTM-480 as the 1V/Oct input that
> affects both the HP and LP filters simultaneously and the resonance CV
> input affects both HP and LP resonance simultaneously.
>
> The CS VCF filter resonance controls provide about 80% of the resonance
> range for the HP and LP filters. On a CS machine, setting these to
> maximum and then using the global resonance control allows for the
> remaining 20% of resonance range to be used. On the MOTM-480, setting the
> individual resonance controls to maximum provides the 80%-of-range, and
> applying some (positive) control voltage to the resonance CV jack provides
> the remaining 20%. I think the maximum "Q factor" is 15 or so (and the
> minimum around 0.5).
>
> The MOTM-480 resonance is the same as the CS-80's. Just try the "funky"
> tone selectors (that is, presets literally labeled 'Funky 1' to 'Funky
> 4') on a CS-80. Or, listen to the Vangelis track "Chung Kuo" from the
> China album at around 1 minute into the piece--the low-frequency notes are
> all done using one of the "funky" presets with aftertouch control of
> filter frequency. In fact, listen to the entire track for a
> nearly-all-CS80 experience.
>
>
> Crow
> /∗∗/