Hackable Analogue Sound Module
The Akai EWV2000 is an analogue synthesizer module intended for use with wind controllers such as the EWI1000. The sound engine is monotimbral and built around two CEM3394 synth ICs, also found in some of Akai’s AX/VX series, the SCI Six Trak, or the Doepfer Dark Energy MK1. Some people may frown at the sound of the 3394, yet my first analogue synth was an Akai AX73, which kind of flashed my taste eproms in the Curtis direction. In the EWV, this comes wrapped in a wonderful industrial design.
Connecting the EWV2000 to CV interfaces/your modular
As regards modding the EWV2000, the most interesting bit night be to create usable CV connections. Since The EWV2000 module does not have any midi input connector, you are either left to your saxophone playing skills or have to resort to some tinkering. There is a DIN midi output and an unpopulated place for a midi input connector on the PCB, but the latter does not seem to be addressed by the CPU.
There is not much information on the interwebs on hacking the Akai for a midi interface retrofit and/or CV input connectivity, but some users mentioned utilizing the wind instrument connector with CV for making noises. I could not find a service manual scan but one for the Akai VX600, which, despite using different CEM ICs, also has a wind controller connector. Since in boths synths, the synthesizer parts are addressed by a CPU, the font end, i.e. the wind controller-CPU connection, can be assumed to be identical. As per VX600 schematics, the wind controller pins are:
Since I had my unit open for a cleanup and servicing some of the stiff buttons, I also transferred this pin mapping to the EVW.
As for establishing your connections, best scheck with a multimeter for GND, -6V and +12V. The rest can be mapped relatively easy with feeding some small voltage to the pins (through a resistor/ diode and resistor for safety). The synth’s CPU scans for these voltages and then transforms them to respective PWM signals (envelopes are digital in the EWV, and the 3394 pitch input is addressed per PWM). Breath/Gate works well with standard gate signals, yet since the EWV allows for continuous breath voltage on assignable parameters such as filter cutoff or vca level, envelopes/LFOs are also sweet options. Glide and vibrato I found very sensitive (useable up to 2-3V).
Pitch CV yes, but can be better
Pitch was a bit of a horror trip. On account of the wind controller having two sets of controls (some metal rolls on the underside for octave selection and some metal plates on the upper side for notes), you basically can play the EWV with CV over one octave or need to send two separate CVs (Reaktor/Max/VCV-style, or via an arduino) in order to sensibly play over more than the range of one octave. Trying another route, I traced the pitch PWM signal after the CPU, which, again, could be adressed by an arduino).
Since I did not want to cut traces or make any other drastic incursions, I eventually went for applying pitch CV at the CEM3394 VCO-CV pins (pin 2 of each IC) directly via a small resistor. This worked with my Expert Sleepers ES4 and pitch calibration per software for both VCOs, although I needed to run pitch CV inverted (lower notes = higher voltage).
Measuring my Doepfer A111-5 directly at the pitch CV input of its CEM3394 while sweeping the module’s pitch potentiometer bore the same results with a range from ca. -1.4Volts for highest pitch to -3Volts for lowest pitch. So, in order to have your pitch CV in mod work properly, you need an additional inverting opamp, just like in Aaron Cram’s schematic here:
http://electro-music.com/forum/phpbb-files/cem3394_v2_163.pdf
Futher mod possibilities and technical aspects
Addressing wave-select CV and PWM CV: you can easily feed CV, as per CEM3304 datasheet specifications to modulate waveform selection and PWM per external CV inputs.
Filter feedback: since the EWV has a headphones output and an External input with volume control, you can resort to one of the oldest tricks in the book and gain some very nice sounding filter overdrive, just by plugging a a cable.
Filter bank: the output signal of the two CEM “synths on a microchip” can be sent through a filter bank circuit that is meant to approximate the EWVs sound to reed instruments. The circuit is basically a row of op-amp based filters that are addressed by different preset settings (I assume different volume ratios of each filter). You can, of course, find the input and output pins of thsi circuit and send other signal sthrough it.
Unused VCA: the EWV does not utilize the inbuilt final VCAs of the two CEM3304s but has another IC for this purpose after the filter output signal has passed though a highpass filter. This might indeed lead to sonic differences between Akais and other synths using that IC, since the VCA part in the CEM has neither an exactly linear nor exponential behaviour.
Ericasynths AS3394 reissue
The CEM 3394 had originally been designed for use in arcade machines (synth on a chip, adressabe per PWM, boom) and priced accordingly. Being then obsolete, second-hand prices shot up, but ALFA/Ericasynths recently reissued it in form of the AS3394 (through hole and SMD versions) chip, that offers a couple of extras, such as ramp out, and added a couple of extras, such as Sawtooth output and an integrated suboscillator. Since the AS has four more pins than the CEM, using it for replacement will come with some adapter action, but I hope that the new availability of this great sounding circuit will lead to new polysynths using it (please Akai 🙂
Since the AS3394 is also a usual suspect for DIY work, you can find here a German thread on exactly this (including info on Aaron Cram’s old schematics).