Digital Keyboards Synergy Preservation Page

I’d like to light a fire under the entire industry right now… I don’t want people to be so complacent about this. We’re really lying back and being satisfied with trivial crap like sampling machines. Not that they’re bad… But it’s musique concrete done in a new way. It’s back to the ’40s and ’50s. That’s all it is. There’s nothing wrong with that, but it’s not a breakthrough. It’s a refinement.

– Wendy Carlos, Keyboard Magazine, November 1986

This page is devoted to information and projects about one of the most sophisticated synthesizers ever made, the Digital Keyboards Synergy, and its offspring, such as the rare Mulogix Slave 32, and its predecessors, such as the extremely rare Crumar GDS.

If you have a Synergy, it’s worth preserving. One tech I talked to estimated that probably less than 100 (of the 700-800 originally made) are still in operation. Slave 32s (essentially a rack-mounted synergy) are much rarer still; only 25-30 were made.

The Synergy has 32 digital oscillators that are allocated to notes as they are played; voices which use more oscillators per note have less polyphony. Each oscillator can play a sine or a triangle wave. The Synergy is primarily known as an additive synthesizer, but you can also do FM on it (although to avoid ticking off Yamaha, Digital Keyboards didn’t make a
big deal about that feature at the time.) It seems underpowered compared to later additive synths, such as the brilliant Kurzweil K150, which has a bank of 240 oscillators. Yet, the Synergy often sounds just as impressive, if not more. I think that’s primarily for four reasons:

  • On the Synergy, you actually specify two complete sets of rates and breakpoints for the envelopes, and the Synergy can smoothly interpolate between the two based on, for instance, velocity information. On something like the K150, the velocity has much more limited control. This is much more complex than a simple crossfade.
  • On the K150, each partial can be set to non-harmonic frequencies, but each partial is then locked to that frequency. On the Synergy, each partial can have its own independent frequency envelope.
  • The envelopes are quite flexible, with up to 16 stages, for both amplitude and frequency. (The Kawai K5000 had only give 5 stage envelopes.)
  • Wendy Carlos went nuts on the Synergy, and spent years refining its voice library. Most of her voices only use two or three oscillators, yet they sound incredible. The fact that she tuned them all by ear – i.e. no FFTs or phase vocoders used! – is remarkable.

Photos of the Inside of a Synergy, and Debugging

I believe this is the only place on a web where you can find such photos. I also include some repair tips (it took a while to get my Synergy fully working, and I learned a lot in the process.)


Synergy/Slave 32 Software


Synergy Schematics

Synergy Mailing List

Yahoo Synergy-Synth: “This group is for discussion of this instrument in all its facets: design, repair, modifications, wants, tech tips, upgrading from the basic unit to the II+ Kaypro version, voicing, sequencing, basic operation and so on. This will be a moderated list for smooth operations.”


Synergy Family Owners List

If you have a Synergy, Slave 32, or (gasp!) a GDS, please drop my a line with whatever info you’d like to include here. Let me know how long you’ve had it, what goodies you have, how you use it, etc. It would be nice to get a feel for how many Synergies are out there.

The Sounds

What does it sound like? The various metallic percussion instruments – vibes, xylophones, etc. – are the most impressive on this beast. They have a complex overtone structure that you just won’t get by filtering a sawtooth. There’s a drumkit that’s mindblowing considering how it’s being generated. The organs and brasses are fantastic too. The strings are a mixed bag; they sound a lot better on Wendy Carlos’ recordings than they do right out of the Synergy. The bow scrapes are impressive, but the strings overall sound bit cheezy, coming out solo straight from the Synergy; I suspect that on the recordings, Carlos is making very careful choices of reverb and EQ, as well as carefully layering them with other instruments. (Definitely, owning a Synergy isn’t going to make you sound like Wendy Carlos any more than owning a Stratocaster will make you sound like Eric Clapton.) The pianos won’t fool anyone; it’s clear that you need a lot more partials to pull off a piano (as the Kurzweil K150 does quite well.)


These are scans of the documents Mark Glinsky (check out his Manual Manor
if a manual exists, he probably has it!) sent me along the the Synergy II+ he sold me. If you have other Synergy/MuLogix/GDS documents, and can send me either PDF scans or a hardcopy, please get in touch with me. I’d like to make this section as complete as possible.

The next two documents are different printings of the same document; I include them both for historical interest.

Documentation from other sources:

Magazine appearances: (thanks to Ramiro Turin for sending these scans):

Circuit Layouts:

The Synergy is based on a digital synthesizer designed by Hal Alles when he was at Bell Labs. This design is extensively documented in two journal papers:

  • H.G. Alles, “An Inexpensive Digital Sound Synthesizer,” Computer Music Journal, Vol. 3, No. 3, Fall 1979.
  • H.G. Alles, “Music Synthesis Using Real Time Digital Techniques,”
    Proceedings of the IEEE, Vol. 68, No. 4, April 1980, pp. 436-449.

Essential Listening

  • Wendy Carlos, Digital Moonscapes (read reviews, and Wendy’s commentary)
  • Wendy Carlos, Beauty and the Beast (read reviews, and Wendy’s commentary)
  • Wendy Carlos, soundtrack to Tron (read Wendy’s commentary)
  • Fred Becker, Inner, Stellar
  • According to Ramiro Tunin, Christopher Franke used his GDS on the “Thief” Tangerine Dream soundtrack, particularly preset 12 (“Xstrings”), and Klaus Schulz used his GDS exclusively on the rare album “Dig It” on the “Brain” label (Side 1: 1. Death of an Analogue, 2. Weird Caravan, 3. The Looper Isn’t a Hooker; Side 2: 1. Synthasy), recorded between May and September in 1980.
  • John DeRosa spotted a Synergy in the video to Hall and Oates’s “Say It Isn’t So.” I have no idea if it was used on the actual recording or is just a prop for a video, but the sound does sound like something the Synergy could do.
  • Kat Epple, who used to be one half of the group Emerald Web, noted that the Synergy was used on the Emerald Web albums Traces of Time, Nocture, Lights of the Ivory Plains, Dramspun, Catspaw, and Manatee Dreams of Neptune, some of which are available from CD Baby.

Synergy Links

Price Info

How much did you pay for your Synergy? They’re very hard to price. I paid $850 for mine (II+, along with Kaypro and editing software). To someone who knows what they are and how important they are in the history of synthesis, they’re worth a lot; but such people are probably rare. I heard of a II+/Kaypro setup going for $1500+shipping in the summer of 2005.


Projects that might be fun for someone to try:

  • Make some modern Windows/Mac software to send voice data to the Synergy over RS-232 (I’ve been looking for a DB-25 style RS-232 interface for the Mac)
  • Make a graphical Synergy voice editor (maybe Java would be good for that?)
  • Design and prototype a new replacement DAC card, or a SPDIF interface card for the digital oscillator, to get pristine digital signals out of the machine.
  • Make an FPGA replacement for the digital oscillator board. The digital oscillator board is around 110 TTL chips – I bet you could fit it in a modern Xilinx or Altera FPGA pretty easily.
  • Create a procedure for rack-mounting a Synergy. It looks quite doable; I’d just be hesitant to hack up my only working Synergy.
  • It would be feasible to grab some Z-80 simulator code, add code to simulate the front panel interface and the memory-mapped hardware, and actually run the original Synergy operating system on your PC. That would be pretty wild. Some folks are doing this for the Wave PPG 2.3, simulating the 6809 and all its peripheral chips.

The technical documentation for the Synergy is quite detailed, so I think all of the above projects are feasible.

If someone is interested in contributing to such projects, please pop me an e-mail!


Before you try finding a repair shop for your Synergy, check out my debugging tips on the
photos page. If you’re still stuck, you might try the following:

  • If he’s available, Paul Schreiber ( is probably your best bet. He owns a Synergy, so if you can nail the problem down to a specific board, you can just send him that board (avoiding the cost of shipping the whole thing, which weighs something like 75 pounds). However, Paul’s time is mostly taken up by the demands of his fantastic MOTM line.
  • Davidson Electronics wrote: “We are quite familiar with these units and their architecture. It is best to send the entire unit to us.”
  • EPR Electronics wrote: “We have the stereo microscopes and surface mount work station needed to repair your [Synergy] unit to a stable and warrantable condition.”
  • David Vandenberg has created many Synergy modifications. He writes: “If anyone wants to send my their Synergy, I’ll be more than happy to try fixing it for them.”
  • If your keyboard is having issues, check out the Universal Keyboard Upgrade from
    Virtual Music. They also have assorted other spare Synergy parts. If you’re in Europe, they might be able to service your Synergy, as they service a lot of old synths, but I haven’t explicitly asked them.If anyone else knows of folks who can fix a Synergy, please let me know and I’ll add that info here.

    Last modified 1/8/2018
    Maintained by Aaron Lanterman