A digitally controlled analog subtracive synth. 8 voice 2oscillator/voice. As to ..exactly what those oscillators are...apparently DCO's as one would think with 16 of them. Synth museum says VCO's as do other sites. I only see a pair of transistors per voice...and they aren't thermally attached nor are their two pairs of them anyway as two real vco's would demand at least.
OK UPDATE. Meant to long ago. lol. I got schematics a while back and indeed this is the same type of circuit as the SX-240 etc. Programmable timers generating the base 'oscillations' in this one. Op amps are pulsed with the dco signal in cooperation with a CV signal from actual sample/hold cells that set the ramp rate of the analog circuit there that is generating the sawtooth waves. But of course the square part is digitally from start to finish. Anyway then once these signals are achieved they are mixed to the CEM3372 VCF used in Chroma Polaris, Prophet 600 and Oberheim Matrix synths in this hummer. And the tuning is perfectly stable and sooo..DCO's no doubt. (Oops...I just found an archived description of the synth from Akai! Fairly nice character though. Nice fluorescent displays for the cool look in the dark. The sound is a bit sterile in some ways but interesting in others. Very similar sounding to the chroma polaris actually in many ways. ALso velocity is fairly lo-res. Probably 3 bit or something crude. But good enough to make some nice clavs etc. 3LFO's, 3ADSR's and MIDI xmit and receive channels (hit patch number for channel you wish to select...)
These machines have very fragile board interconnects. FLexing of the panel stresses them and they often crack and cause switches or segments in the display to drop out. The best fix I've found is to scrape back the traces and to solder over them AFTER DISCONNECTING SYNTH AND POWER SUPPLY! I had a cap discharge and mess up something on on cpu board I thought! Turned out it just blew some of the mux chips that are on the front panel. In any case be sure to disconnect the actual headers from the power supply! Dont' risk it! But getting solder along a fatter amount of trace or even putting some fine wire fluxed in there and soldering it will make a very reliable connection.
My synth had other problems. Looked like someone cracked one of the boards with a hammer. Could be the whole case got flexed? I dunno. But anyway watch for that sort of thing...I guess. I've only heard of a few cases of filter chips dying but otherwise these are a pretty solid unit from all I've heard.
NOTE: Regarding CEM3372 VCF's. We had a recent bit of experience trying to get these to work in Doug Terrebone's Prophet 600 and in one I had here. None of the stock I had would sound the same (not to mention that two I got from chipforbrains some time back were totally doa... bummer. Thought those were NOS!) They lacked the whispy overtones with Resonance all the way up in particular. THey were all "C" revision. The "B" rev's were in the P600's but Doug said he finally got in an AX80 that had Rev "C's" and those worked fine! Go figure! Anyway just beware that there is some variation in these chips.
Let me know if you need a specific part from my listings in the parts section.
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Akai Professionals description (Pulled from archives. No longer a live page...)
The AX80 was Akai Professional's first musical instrument - an 8-voice analogue programmable, polyphonic synth. It had an impressive spec and a unique user interface.
Each voice had two independent audio oscillators that offered sawtooth and square waveforms and a 'mix' setting that offered both simultaneously. The oscillators were analogue but were 'digitally controlled' for better pitch stability and tracking. (*editors note*: These apparently are possibly a digitally pulsed sawtooth core. So square and pulse waves are purely digitally generated in essence and saws are created with an integrator circuit with a digitally generated CV to modulate the ramp rate, similar to many other synths of the day. Disregard prior note, I'd misunderstood something way back on these things...) Oscillator 1 offered pulse width modulation (PWM) with its own independent LFO. It also offered a sub-octave that effectively gave the AX80 three oscillators per voice. Oscillator 2 offered similar facilities (except PWM and the sub-octave) but added cross modulation (hard and soft oscillator sync), and variable pitch modulation by one of the envelope generators. Naturally, both oscillators had variable octave settings (16', 8, 4' for Oscillator 1 and 16', 8', 4' and 2' for Oscillator 2) and the two oscillators could be detuned.
The lowpass filter used the same Curtis CEM 3372 chips as the Oberheim Matrix synths and Prophet 600 and sounded warm and musical. There were controls for cutoff frequency, resonance, envelope modulation, keyboard tracking and velocity. The filter also had its own dedicated LFO. The AX80 also had a static highpass filter
Three ADSR envelope generators were provided - one for filter, one for the amplifier and one that serviced both VCF and VCA. These could also be routed to Oscillator 2 for pitch sweeps. The envelopes had variable 'key follow' so that overall envelope times could be governed by keyboard position.
Each voice also had no less than three LFOs - one for Oscillator 1, one for Oscillator 2 and a third for the filter making it possible to create some very thick lead and pad sounds. Each LFO offered square, sawtooth down, sawtooth up and triangle waves plus a delay parameter and, of course, a speed control.
There were 32 factory preset memories and 64 user-programmable memories. (I corrected this. They said there were 64 preset and 32 user. Not so. 32 preset and A and B banks of programmable patches of 32 each. )
Programming was typical of the day using 'parameter access'. In the EDIT mode, you would first select a parameter to tweak (using the same buttons that normally selected sounds) and you used the large DATA ENTRY wheel to set that parameter's value. On most (if not all) synths that employed this method, this was a frustrating experience because you could only see one parameter at a time and because of this, you couldn't see the other parameters and how they interacted. The unique user interface of the AX80 overcame this with the use of a row of a flourescent displays that showed the value of each parameter/control very graphically.
The AX80 also had many convenient 'performance' facilities. The mod wheel could be routed (with dedicated buttons) to either pitch or filter cutoff (with a variable 'range' control) and the DATA ENTRY wheel could also be assigned as an extra performance control. The pitchbend wheel also (uniquely) had a dedicated, variable range control. There were also dedicated level and tune controls in the left-hand 'performance' area of the instrument. The AX80 also featured a dedicated HOLD function (for hands-free sustain of sounds) and a dedicated CHORD MEMORY button whereby playing a chord could be 'memorised' and then played from one key.
Overall, the AX80 offered many new and unique features not found on other synths of the time. It also sounded great! In hindsight, some of the factory presets were perhaps not as strong as they could have been but these were early days for us - many AX80 users will provide testament to the broad range of analogue synth sounds that can be coaxed from the instrument... from fat basses to thick pads, searing leadlines and more.
If the AX80 had a problem, it was the timing of its release. Akai Professional came to the market with the AX80 at almost exactly the same time as the Yamaha DX7 was released. The AX80 was similarly priced ($1,500) but, unfortunately (and like so many other manufacturers of analogue synths at the time), the AX80 could not not compete with this new 'flavour of the month' synth. In all honesty, it didn't help that we were new on the scene at the time!
However, the AX80 was a fine sounding analogue synth with many unique features that elevated it above other similar synths of the time. Fortunately for potential buyers of used AX80s, used prices are low and because the AX80 doesn't enjoy the same reputation as maybe other similar synths of the time, you can expect a bargain for this underrated analogue polysynth.