CS-80 Filter for Shruthi @ MuffWigler

I did not know someone rather than @tubeohm working on a new filter for Shruthi.

CS-80 Filter for Shruthi

Nice! But… the CS-80 is designed for a poly synth. Will it be any good for the Shruthi? Keen to hear some demos.

I had wondered why Tube Ohm and Laurentide weren’t offering the Dual SVF as an option. Makes sense now.

The reason is you won’t squeeze ad DSVF on an Ambika Voicecard without changing its size or go SMT. Please don’t inherit a n urban Myth that there are filters that are only suitable for Polyphonic Synths……

You’re right. I automatically equate monosynth with bass and polysynth with pads and chords. But as I well know, Shruthi is great for leads and arps. And so is the CS-80 :slight_smile: Even more keen to hear demos now.

Cool. I wonder what are the differences between this and the original dual SVF - the layout appears to be very similar!

Actually, the only difference I can see is 2 missing op-amp cell (very probably an “optimization” routing the output of one 2164 cell right into another one in the Q control - something that did not cross my mind until I checked the schematics today!).

As far as I can tell, it’ll be CS80ish “in spirit”, as in “two cascaded SVF” - not a component-by-component clone. One could even get away with all the switching/routing logic and hardwire to the HP->LP configuration. So all Mr Jourdains who got the original dual SVF/Midnight, be reassured… You already own a CS80 filter :smiley:

I am excited by the possibility of a CS-80 Ambika card, with poly aftertouch enabled, closest I´ll get to a real one anyways

Scott is definitely the right person for this job


Will this need any special firmware to work? or can I just plug this onto my PVK control board?

I expect stock firmware will work for this. At a guess you’d need to select the dual SVF mode for it?

I’m eagerly waiting for the release of the schematics to know in which way it’s different from the SVF!

In the store it states it is based on the Motm480 mk2. The circuit for the Motm 480mk1 is based on the Jurgen Haible circuit. This circuit has 4,7Mohm resistors parallel over the ota. This limits the low cutoff range according to the Jurgen Haible information. There is also a 180p capacitor in the resonance circuit which limits the high reso frequencies. I think these are the main differences with the SVF.

The MOTM480 mk1 was not based on Jurgen’s circuit but was devised from analyzing the IG00156 datasheet. Jurgen and I did talk a lot about Yamaha custom parts 14-15 years ago, and he ran some SPICE simulations that we discussed at length after I had shown him what I did. I still owe many thanks to him in any case for his help back then as we gained a clear understanding of the high-pass phase shift characteristics that are one of the secrets to the CS timbres.

The mk1 circuit had to be retired when the CA3280 was EOL’d. I switched to the V2164 after reading Olivier’s white paper on the device, deciding it would work even better–and it did! It is a much quieter filter now. The only extra stunt I pulled was using one cell for resonance in each filter section without its own buffering op-amp, figuring the virtual summng node at the HP opamp would work in that regard.

I would not mind making an Ambika CS80 voice card, but I would need more CV channels than are provided at the moment. I would need four PWM channels, which might be possible if another PWM timer is available in the 328.

this for ambika would be the goods. I do love the monophonic CS line for dancehall bass though.