Birotron B90 (1975–1978)

At 19 tape players humming beneath a 37-note keyboard, it’s less an instrument than a controlled mechanical avalanche.

Overview

The Birotron B90 wasn’t built to last—it was built to fulfill a vision, brief and brilliant, before vanishing. Conceived by American engineer David W. Biro and bankrolled by Rick Wakeman of Yes fame, this electro-mechanical keyboard emerged from the same sonic soil as the Mellotron but aimed to fix its predecessor’s flaws: tape wear, mechanical fragility, and limited polyphony. Manufactured between 1975 and 1978 by Birotronics Ltd., the B90 replaced the Mellotron’s complex mechanical tape start-stop system with a radical electrical switching design. Instead of moving tape for each keypress, the B90 used solenoid-driven head shifts and fader potentiometers to crossfade between stationary loops, theoretically offering smoother playback and longer tape life. It was a machine of contradictions—ambitious yet short-lived, revolutionary yet doomed by timing.

Wakeman didn’t just fund the Birotron; he shaped it. His name appears on a 1980 patent (US 4,182,214) assigned to Birotronics Ltd., refining the multi-track cartridge mechanism with a common capstan and movable playback heads to enable stereo output and improved track selection. The instrument found its way into his 1977 solo album *Criminal Record*, Yes’s 1978 release *Tormato*, and the live recordings compiled on *Yesshows*, where its lush, orchestral textures colored tracks like “Don’t Kill the Whale.” Electronic acts Tangerine Dream and Earthstar also reportedly used it, drawn to its unique ability to layer real instrument recordings with real-time control.

Still, the B90 was a creature of its moment—and that moment passed quickly. Only 13 units were ever produced. By 1979, Birotronics Ltd. collapsed, its fate sealed not by poor design but by the sudden arrival of affordable polyphonic synthesizers and early digital samplers. These new instruments offered comparable sounds without the mechanical complexity, maintenance headaches, or sheer bulk. The B90 became a footnote, its legacy preserved in myth and a handful of surviving units.

Specifications

Manufacturer	Birotronics Ltd.
Model	B90
Type	Electro-mechanical keyboard instrument, tape loop keyboard
Production years	1975–1978
Keyboard	37-note keyboard
Sound source	19 independent 8-track cartridge players
Sound selection	Each cartridge providing up to four selectable sounds distributed across two keys
Controls	Real-time control via knobs for volume, attack, decay, and pitch
Tape format	Endless magnetic tape loops stored in 8-track cartridges
Tape length	Approximately 10 minutes of tape per cartridge
Tape speed	Standard 8-track cartridges operated at 3¾ inches per second
Original price	Around £1,000 each

Key Features

19 Independent 8-Track Cartridge Players with Electrical Switching

Unlike the Mellotron, where pressing a key physically started a tape strip moving, the B90 kept its 19 cartridges running continuously. Each cartridge contained an endless magnetic tape loop, and when a key was pressed, the system electrically routed the appropriate playback head’s signal to the mixer. This eliminated the mechanical wear associated with repeated start-stop cycles and allowed for longer, uninterrupted playback. The design, patented in 1977 (US 4,018,127), relied on solenoid-driven head shifts and fader potentiometers to smoothly transition at tape splices—critical for avoiding audible clicks or dropouts during sustained notes.

Movable Playback Heads and Common Capstan Mechanism

A later refinement, detailed in a 1980 patent co-invented by Rick Wakeman, introduced a common capstan shared across tracks within a cartridge, improving tape stability and synchronization. The movable playback heads allowed for dynamic selection of different tracks on the same cartridge, enabling stereo output and more flexible sound layering. This was a significant technical leap over fixed-head systems, offering greater control and sonic depth without requiring additional mechanical complexity for each voice.

Real-Time Knob Control for Volume, Attack, Decay, and Pitch

While many tape-based keyboards of the era offered fixed envelopes, the B90 gave players real-time control over volume, attack, decay, and pitch via front-panel knobs. This made it unusually expressive for a tape-replay instrument.

Historical Context

Born in the mid-1970s as a direct response to the Mellotron’s limitations, the B90 represented the pinnacle of tape-based keyboard technology. It attracted interest from major musicians of the era, according to SynthDB, who were drawn to its combination of orchestral realism, real-time control, and—despite conflicting reports—claims of a lighter weight and more compact size. Yet its development coincided with the dawn of digital sampling and polyphonic synthesis. Instruments like the Fairlight CMI and Prophet-5 offered comparable sounds with far greater reliability and flexibility, rendering the B90 obsolete almost as soon as it arrived. With only the B90 in its lineup, Birotronics Ltd. had no fallback when the market shifted, and the company folded in 1979.

Collectibility & Value

With only 13 units ever built and Birotronics having destroyed prototypes and specialized spare parts after bankruptcy, the B90 is among the rarest instruments in progressive rock history. By the 2010s, only a handful were known to exist, and reports from 2015 suggest as few as two remained functional. It has been called “music’s rarest instrument” across multiple sources, including Facebook groups and Reddit discussions. In 2011, Rick Wakeman reportedly offered his personal B90 for between $1,500—a figure that, if accurate, seems astonishingly low given its scarcity, though it may reflect the instrument’s unreliability and lack of serviceability. Collectors are warned that some software libraries claiming to emulate B90 woodwinds may be misleading, as no such recordings were ever made for the instrument—posing a risk of misrepresentation in sample packs.

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