Roland IR3R05 custom vca/vcf

[Hermes]

Hi guys

I was taking a look on ebay about roland analog stuff and i came accross an auction of a Roland IR3R05 custom vca/vcf (this is use in the Roland MKS 80 analog synth module and MKS 70 digital analog hybrid synth module).  

The seller claims that this chip could be used in a custom design as a moog filter/curtis amp (a 2 in 1 package)   :D

The question is: Does anyone have any idea if and how this could be of any use to the community?

If you want to take alook the link is:

 

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=64386&ite m=3760323550&rd=1

When I saw this I just imagined a 4xSID output going thru this filter amp - crazy or what? 8)  

Cheers

Hermes

[AndrewMartens]

It's an interesting idea, but the lack of general availability of the chips might make it of somewhat limited usefulness.  

While working on my MBHP SID project (and toying around ideas for my MBHP POKEY and PSG synth projects), I started looking into some hybrid digital/analog synth projects.  Currently I'm considering using a PIC as a digital oscillator, and running it through an analog VCF/VCA.

Using SSM and CEM chips makes designing analog circuitry easier, but there's not many of them to go around.  Fortunately, there exists the LM13700 OTA (operational transconductance amplifier).  There are some simple circuits out there (for example, the 13700 datasheet) that illustrate how to use half of one chip as a VCA.  One 13700 can also be used at a 12 dB (2-pole) filter - chain two of them for a 24 dB filter!

If one searches Google for "Juergen Haible Wasp Filter Clone", you'll find a clone of the filter section from the Wasp.  I'm planning to swap out the no-longer-available CA3080s with a 13700 filter section.  Hopefully it'll sound cool _and_ have the parts be available from most suppliers.

A MBHP Core with an AOUT module would be great to output envelopes, LFOs, etc. which in turn could be connected to analog VCFs and VCAs...