OK, now that the GX1 VCBPF is now the MOTM-475, time to elaborate:
The GX1 has four filters per voice. Two highpass, one bandpass and one
lowpass. One highpass filter takes its input from the variable-pulse
waveform of the VCO, and has a level control on the output. (There is
also a switch to enable the unfiltered pulse waveform). The bandpass
filter has the sawtooth as its input, and a pair of switches allow the raw
sawtooth, the BP-filtered, both or neither to be sent on to the main VCF.
The main VCF is in fact one highpass filter and one lowpass filter in
series. The input is from the VCO waveforms (some switched, some
filtered, some level-controlled).
The MOTM-485 is one-half of the "main" GX1 VCF. Two MOTM-485s are
needed--one set to HP, one set to LP--to form the "main" GX1 VCF.
The MOTM-475 is the bandpass filter that, on the GX1, is a fixed-Q
2nd-order harmonic selector used to pick out individual harmonics from the
sawtooth waveform. In MOTM form, the Q is variable and the FM input is
the reversing type.
Two MOTM-485s can form a 2nd-order bandpass with separate HP and LP
corners and Qs, whereas the MOTM-475 has one BP (with "fixed corners")
control and Q. They behave somewhat differently as a result.
For completeness, the MOTM-480 is also an HP/LP pair in series, in one
module, using a different filter topology.
Crow
/∗∗/
On Wed, 16 Feb 2005, edibennardo wrote:
> .. Wait a minute! I was planning to purchase a second 485 for the
> couple, do you mean I can have a GX1 bp couple with one 475 alone?
> (this means many things to me: I could purchase more 475s for a small
> polyphonic project but means also one more chance to hope to see it
> included in an SE Omega 8 setup???)In the end which differences could
> be encountered between a 485 and a 475?
> Regards Enrico (Sicily)