[sdiy] Oberheim Xpander VCF

[Adam Schabtach]

I have one of Marc's PC boards for that add-on. It's one of my back-burner
projects; I haven't finished it because I've been waffling over how I want
to do the panel and the mode display. I really should at least get it to the
point at which I can test it. I used to have an Xpander and the filter was
probably my favorite part of it. I have two MOTM-440 filters and like them
very much, so giving one of them a number of different topologies is very
attractive to me.

I attempted to reduce the gain errors by hand-matching 1% resistors. I also
realized that many of the resistance values form simple integer ratios, so I
used resistors in parallel, chosen to create the required ratios as
accurately as possible. I don't know how much it will actually help but it
seemed like a good idea at the time.

--Adam

> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl 
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of David Moylan
> Sent: Thursday, January 15, 2009 8:26 AM
> To: George Hearn
> Cc: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Oberheim Xpander VCF
> 
> This type of versatility is available to cascaded integrator 
> filters in general, by mixing outputs of the separate stages. 
>  Marc Bareille created an add on for the MOTM-440
> 
> http://m.bareille.free.fr/modular1/vcf_multimode/extrapole.htm
> 
> Although it's nice to be able to switch in discrete steps you 
> can probably have some fun with a 4 way mixer as well.
> 
> Dave
>