Akai VX90 (1986)
Rack-mount 6-voice analog synth module with CEM3394 chips, menu-driven interface, and MIDI control, identical to the AX73.
Overview
The Akai VX90 is a 2-rack-space, 6-voice analog synthesizer module made in 1986 as the rack-mount counterpart to the Akai AX73. The voices are fully analog and built around the CEM 3394 voice chip, with one VCO per voice. The VCO makes saw, triangle, pulse, a saw+triangle mix, and noise. There is a 24dB/octave resonant low-pass/high-pass filter, ADSR envelope control, and a single LFO. It has no keyboard and is entirely menu-driven through an LCD with a backlight LED. MIDI runs on a global channel. It is not multi-timbral.
Specifications
| Polyphony | 6 Voice |
| Oscillators | 1 VCO per voice (6 total) with saw, triangle, pulse, saw+triangle mix, and noise |
| Filter | One 24dB/octave (4-pole) resonant low-pass/high-pass (VCF) |
| Memory | 100 patches |
Design
The VX90 has the same voice structure and firmware as the Akai AX73, and the CEM 3394 analog voice chip makes the sound. It has an auto-tune function and is controlled entirely through a menu-driven interface with an LCD and backlight LED. Inside are UPD8255AC microprocessors, an EHK-MD6207 DAC, LF356N op amps, and 4051 analog multiplexers. Some units use ALPS SPPQ19 tactile switches, which are known to fail over time. The original power supply delivers +/-15v, +/-6v, +/-5v (analog), and +5v (digital). Tauntek makes an updated EPROM that enables MIDI control of all parameters, and a third-party power supply design improves on the reliability of the original.
Context
The VX90 is the rack-mount version of the Akai AX73 synthesizer. It has the same analog sound engine in a format meant for the studio. External audio from Akai samplers like the S-612, S-900, and S-950 can be run through its filter and envelopes. Patches are stored as FSK audio on cassette. SysEx is not supported. Firmware versions are V1.1 (April 01, 1986), V1.2 (April 29, 1986), V1.2a (June 04, 1986), and V1.4a (January 20, 1987). Service bulletins MS-0009, MS-0010, and MS-0017 for the AX73 also apply to the VX90.
Market
The ALPS SPPQ19 tactile switches fail and can become unresponsive. The system can also lock up during the auto-tune function. Tuning instability and erratic voice behavior are reported too. The MD6207 DAC chip is rare and hard to replace. The service manual and schematic are available, and repairs may mean cleaning switches or modifying replacements. Replacing the backlight LED often requires adding a current-limiting resistor. The VX90 is noted for a wide, sometimes harsh tonal character, and people praise specific presets like "Heaven." Its "noisy BBB chorus" circuit is a known trait.
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