M A Ruberto Synthacon VCF with Turbo switch

elmegil

I bought an M A Ruberto Synthacon VCF PCB for which we have a parts list, but no schematic or wiring diagram. I've done some googling and found that M A Ruberto is also Somnium 7, and this PCB was discussed on the Synth DIY list back in 2007, but any links to anything like schematics are dead and not recoverable with web.archive.org. Nothing here or on Muff's of much help either.

Lest anyone take it wrong, this is not a complaint, it was a good price Smile

But I'm trying to cast about and see if anyone has any additional information about this PCB. Unfortunately my attempts to email the Synth DIY list itself (I am a member for some time) don't appear to be going through, for reasons unknown. I've emailed the list owner, but no reply to figure it out so far. I've also attempted to contact Mr Ruberto through Somnium 7's soundcloud page, but again, no reply so far.

I've started mapping out the circuit in Eagle so I can compare to other Synthacon VCF schematics, but it's slow going, of course.

Any information is welcome Smile

elmegil · Posted: Sat Feb 23, 2013 12:45 pm Post subject:

Got an answer over on Muff's sharing here for completeness if someone else ends up in this boat Smile

http://www.muffwiggler.com/forum/post-1087618.html#1087618

elmegil · Posted: Sun Mar 24, 2013 9:44 pm Post subject:

I finally have this built, and I'm having a couple of issues.

1) I only get sound when I have the turbo switch on. I'm totally not clear on what the FET is supposed to be doing, but that is in fact the only substitution I've made in this circuit--I used a 2N5458 rather than 2N4302 because I had one on hand, and things I read online suggested that was a legitimate sub.

2) The cutoff frequency is really only useful in the last 1/3 of its rotation CCW. For low pass, after that, the rest of the way CW, I'm pretty much passing everything. For high pass I get some pass through up to 50% but after that it's entirely cut off the whole rest of the way around. I hooked the lowpass up to a frequency analyzer, and with the cutoff set fully CCW and the Resonance at about 2/3's (so it wasn't screaming at me), my cutoff appeared to be somewhere between 3 & 4 Kilohertz.

I'm looking at the cutoff setting, and I also looked to compare to the YuSynth Synthacon that is also done with a 2SC1583, and the voltage swing is essentially the opposite--The Ruberto version, per the schematic, ranges from 15V to ~4V, whereas Yves' version ranges from 7.5V to Ground.

I'm considering swapping that 20K resistor to the 15V side rather than the Ground side, to see if that behaves better.

synthacon_vcf_rev5_scm_398.jpg

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slightly cleaned up from the schematic posted on Muff's

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