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 produced in 1986 as the rack-mount counterpart to the Akai AX73. It features fully analog voice architecture using the CEM 3394 voice chip, with one VCO per voice generating saw, triangle, pulse, saw+triangle mix, and noise waveforms. The VX90 includes a 24dB/octave resonant low-pass/high-pass filter, ADSR envelope control, and a single LFO. Designed for studio integration, it lacks a keyboard and is entirely menu-driven via an LCD with backlight LED. It supports MIDI on a global channel but 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 shares identical voice structure and firmware with the Akai AX73, using the CEM 3394 analog voice chip for its sound generation. It features an auto-tune function and is controlled entirely through a menu-driven interface with an LCD and backlight LED. The unit contains UPD8255AC microprocessors, an EHK-MD6207 DAC, LF356N op amps, and 4051 analog multiplexers. Some models use ALPS SPPQ19 tactile switches, known to fail over time. The original power supply delivers +/-15v, +/-6v, +/-5v (analog), and +5v (digital). An updated EPROM from Tauntek enables MIDI control of all parameters, and a third-party power supply design improves on the original’s reliability.
Context
The VX90 is the rack-mount version of the Akai AX73 synthesizer, offering the same analog sound engine in a format designed for studio use. It can process external audio from Akai samplers like the S-612, S-900, and S-950 through its filter and envelopes. The unit supports patch storage via FSK audio encoding over cassette but does not support SysEx. Firmware versions include 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
Common issues include failing ALPS SPPQ19 tactile switches, which can become unresponsive, and system lockups during the auto-tune function. Tuning instability and erratic voice behavior are also reported. The MD6207 DAC chip is rare and difficult to replace. The service manual and schematic are available, and repairs may involve 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, with praise for specific presets like "Heaven," and its "noisy BBB chorus" circuit is a known trait.
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