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How to Hack Your Vintage Analog Synth

Tips from a French Computer Programmer Named Gligli
November 4, 2013, 4:30pm

Things are pretty good right now for synth geeks. In addition to the array of analog synths that have slowly and steadily become trendy and readily available, the world of DIY electronics has been growing rapidly. From dudes doing amazing things with the versatile Arduino platform to the now-well known Juno 60 MIDI retrofit kit, people are no longer afraid to open up an old synth and go to work.

One such DIY spelunker is a man known curiously as Gligli, a restless French computer programmer with an obsession for the Sequential Circuits Prophet 600. Released in 1982 and claiming to be the first synth commercially available with MIDI connectivity, the six-voice, Dave Smith-designed synth never really took off, largely overshadowed by its big brother, the more flexible (and far more expensive) Prophet 5. But Gligli saw something in the less-revered Prophet 600 that most overlooked, and by using his background in programming to create a new firmware, he was able to open up a whole new world of sonic possibilities for the 30-year-old instrument. I tracked down Gligli (whose real name happens to be Fabrice) and we talked about his background, what got him into synthesizers, and what else he has tucked up his sleeve.

Noisey: So, how did you get into synths?
Fabrice: Some years ago, I found a French website about analog synthesizers. There, I found all the sounds I loved from 70s/80s music: Jean Michael Jarre, Tangerine Dream, Kraftwerk, new wave…

What was it called?
It was called but it shut down. is sort of the successor.

dave smith roger lynn

Creator of the Phrophet 5, Dave Smith (left) and Roger Linn, proving that their creations are 100% portable.

And your background in programming was another entry point?
Yes. I'm 32 now, and I’ve done electronics/computer programming stuff since I was about 11. For my day job, I write actuarial software for insurance companies—sounds dull, but it's actually kinda fun, sometimes. What I like the most is when these two domains work together—embedded stuff, low level, bare metal programming.

So have you always had synthesizers around? Are you a musician or collector? I know people love to fetishize old vintage synths but not everyone actually plays music with them.
I bought a Korg Mono/Poly, and started composing with it. Then a few more. I always wanted a Prophet 5, but it was like $3500. I thought the P600 on paper looked almost as good. It’s really only sub-par because of the slow CPU, which basically generates control voltages and gates.

Similar to the Prophet 5, which of course was legendary when it was first released. It combined analog circuitry with a small CPU that offered digital control.
Yes, the P5 was revolutionary in terms of architecture. It brought digital storage of patches.

So you knew you had a lot of potential to work with in the P600. I think a lot of people weren’t aware of how similar it is to the P5. How did you figure out how specifically to program for the 600? How much research was involved?
It involved finding the service manual / schematics, then the firmware ROM file. Then writing a P600 emulator on PC, to study the hardware. Of course it made no sound, it just displayed CVs and gates.

How did you go about writing the P600 emulator?
Well, I love console emulators, and I had written a few before. Same stuff basically. The P600 and the old Sega master system share the same CPU.

So in terms of computer processors, it's relatively simple. We aren't talking a modern super-computer here. What were the significant upgrades you wanted to achieve with your updated firmware?
Better refresh rate of pots. Hugely better envelopes, with proper exponential "analog" shapes. More, wider modulations, and pre-filter overdrive.

And those changes all in conjunction really opened up the sonic possibilities of the P600. In particular the sluggish envelopes were a common complaint, and this firmware update brought the envelopes to lightning quick rates.
Yes, definitely.

So, what other possibilities do you see in the future for combining new and old technology in synthesizers?
I'm not sure I will work on another upgrade like this one, but my latest project is a fully DIY hybrid polyphonic synth using vintage filters and a modern ARM processor.

How did that grow out of the P600 project?
I learned from the P600 hardware, and used the P600fw code as a basis. I just used soft wavetable oscillators instead of VCOs. I designed the PCBs and all.

So what exactly is a soft wavetable oscillator?
Basically something that plays a wav file endlessly at a given pitch, the wav file being one cycle of a waveform, from basic saw/square/sines to violin/voice samples. The modern Waldorf synths and NI Massive VST both use wavetables.

What are you going to call your synth?
It'll be called "Overcycler." The source code and schematics are free and can be downloaded at my site.

Nice. Are you excited about any other DIY synth projects? It seems like having a community to bounce ideas off of would be prudent with these things.
There's a lot of cool DIY projects I know of. The Mutable Instruments have been a great source of inspiration. Many vintage clones projects. The Volcas are really cool for modern synths, and it seems like Korg will keep releasing more and more ambitious analog synths!

Leo ❤ synths and he's on Twitter - @LeoMaymind.