More with MV Sync

[k brown]

I got so enamoured of the look of the knobs and switches on SpaceOhPlex and SpaceOhRack, that I immediately wanted a synth with that look. My first thought was that I don't think I've ever seen a synth (hard or soft) with chicken-head knobs! - why not? They were (and still are) pretty popular on guitar amps, and vintage studio effects and such, but never a synth that I know of.

In casting about for a likely candidate, I landed on my ancient and very ugly, pathetic attempt at an Elka Synthex emulation. The GUI was a very early effort and drab, drab. Not that crazy for the real thing's look either. So, perfect for an almost-ground up re-do and totally different look, especially with Martin's sync, because the Synthex was famous for it's sync sounds.

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maGGi.fsm

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This is essentially finished and has a handful of presets so far.

BUT - In researching the Synthex, I learned that it's designer, Mario Maggi, had just previously completed the first computer-controlled synth with presets, etc., the MCS 70. He was in the midst of showing this at the European trade shows when the Prophet 5 was announced. The MCS 70 was a mono-synth, so production was halted while he set about designing what became the Synthex. However, even though the MCS was a monosynth, many of it's synthesis features were not carried over to the Synthex (three oscillators, linear FM from 3 to 2 and/or 1, dual filters, LFO went up to 300Hz, much longer envelope times, the two EGs could be used on either/both filters and/or the VCA, etc.), so perfect candidate for an FS poly version.
Continued below :

[k brown]

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maGGi 70.fsm

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[k brown]

One issue is, I'd like to gather some educated speculation about the function of a switch in oscillator 1. Correlating the photo against the spec sheet, I can account for and have implemented all the osc switches bit this one - it's legending can't be read in the blurry photo, and it doesn't seem to relate to any of the functions mentioned in the specs - I'm assuming it's something the spec sheet just doesn't mention. Anyone care to guess? The Zip contains the spec sheet and the high res, but not very sharp photo of the whole synth.

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MCS 70.zip

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[Spogg]

...but one thing has me completely stumped - I can't the dang LFO LEDs to flash! I've used the same LEDs the same way several times before, but I cannot get them to work here - have no idea why.

I’ve changed some stuff as detailed in the change log in the schematic.

The LEDs flash now (while a channel is open, because the LFOs are poly).

But if anyone can explain exactly why my solution (point 3) was necessary in this instance, I would love to hear it.

I don’t know about the other queries raised at this point.

Nice synth again Kevin!

Cheers

Spogg

[Spogg]

Having thought about it a bit, the dual Portamento control might be achieved by using the MIDImono prim. This tells you the number of notes currently pressed.
So for one or zero notes (staccato) one setting is selected and for more than one note (legato) another setting is selected. I’m not sure if that’s what the original did and of course it won’t be any good for polyphonic.

That’s all I can come up with at the moment…

Cheers

Spogg

[k brown]

Thanks so much for ironing that out - it's especially puzzling because the exact same LFOs and LEDs are used in maGGi 70 and work without this kludge; very strange.

Both schems replaced with your changes. Didn't know using dezips that way was an issue, given that they have stream inputs, but I'll take your word for it! I replaced them with slew limiters - I've found that modulating VCAs with instantaneous-change shapes like saw and square (even with Martin's band-limited LFO oscs) make nasty clicks, the slews remove that.

I'll have a go with the MIDImono prim and see what I can figure out, thanks for the tip.

[deraudrl]

The other issue is, I'd like to gather some educated speculation about the function of a switch in oscillator 1. Correlating the photo against the spec sheet, I can account for and have implemented all the osc switches bit this one - it's legending can't be read in the blurry photo, and it doesn't seem to relate to any of the functions mentioned in the specs - I'm assuming it's something the spec sheet just doesn't mention. Anyone care to guess?

Ok, I'll take a stab: the switches at the top-left of VCO1/2 enable the AM from VCO3. The switch over the VCO1 Level knob enables the FM from VCO2 (not where I would have put it myself, but so it goes). That leaves the switch above the Fine Tune knob on VCO2: my guess, based only on its location and the presence of a 'Master Tune' knob on VCO1, is that it locks the tuning of VCO2 to VCO1.

[k brown]

Ooops, I see now I didn't state my question clearly - I'm only referring to the switch on the right, above and to the left of osc 1's Level knob; all the switches on the left side I figured out. The upper left switches in 1 and 2 activated FM from osc 3. The sw above the osc 2 Fine tune is the 1x2 AM sw. That leaves only that sw in osc 1 next to the Level knob - ??

[deraudrl]

Ooops, I see now I didn't state my question clearly - I'm only referring to the switch next to osc 1's Level knob; all the switches on the left side I figured out. The upper left switches in 1 and 2 activated FM from osc 3. The sw above the osc 2 Fine tune is the 1x2 AM sw. That leaves only that sw in osc 1 next to the Level knob - ??

Ah, yeah, sorry, I got AM/FM backwards in my description.

Clearly one of those two has to be the AM enable, but it seems like that function should be in the VCO1 line, since that's the one being modulated. And you'd think it would be over to the right next to the (amplitude-related) Level knob.

[k brown]

I think you might be right - the spec sheet says AM, VCO 1 modulated by VCO 2, so that one by VCO 1's Level knob must be the AM sw, and probably is labeled 'VCO 2 AM'. So the mystery sw is actually the one by VCO 2's Fine Tune - I thought the label looked like '... ... AM', but it's actually quite illegible. The other switches are logically placed, so it must have something to do with pitch, being next to the Fine Tune knob. The label looks sort of like '... TO AM', so maybe it in some way changes the signal sent to VCO 1's Ampl Mod? Inverts it maybe?
I'm thinking the clue might be in the fact that VCO 2 is one of the mod sources in the CV 2 section, but that switch isn't labeled 'KYBD', as the one in VCO 3 clearly is. So maybe that switches VCO 2 into LFO range, but it remains connected to the keyboard - that would certainly be an interesting option.
Hmmm. . .