Released in 1982, the Alpine AL-90 was the flagship model in Alpine’s high-end cassette deck range. It combined a three-head configuration, a three-motor direct-drive transport, closed-loop dual capstans and an automated cassette calibration system intended to establish optimised recording conditions for different tape formulations. The deck supported Normal, ferrichrome, chromium dioxide and Metal tape, with Dolby B and Dolby C noise reduction.
The Alpine AL-90 used separate recording and playback heads mounted within a single head assembly, allowing professional tape/source monitoring while recording. Alpine selected a Sendust recording head because of the material’s high magnetic saturation point, which permitted recording across a wide dynamic range. Its recording gap measured 3μm. The separate ferrite playback head used a considerably narrower 0.8μm gap, selected for high-frequency playback performance and reduced eddy-current loss.
Alpine developed the head assembly with attention to azimuth, tape tracking and head-to-tape contact. A hyperbolic head profile was used to reduce low-frequency response irregularities caused by the contour effect. The erase system used a dual-gap Sendust and ferrite junction head.
The transport employed a closed-loop dual-capstan system designed to maintain constant tape tension and stable head-to-tape contact. One capstan was directly driven by a servo-controlled DC motor, while a second motor handled reel drive, rewind and fast-forward operation. A third motor powered the computer-controlled switching of the transport modes. These functions were operated through feather-touch sensor controls.
When a cassette was inserted, the transport briefly entered rewind mode to remove tape slack and establish suitable tape tension before operation. Once this process had been completed, the deck was ready for recording or playback. The transport achieved a specified wow and flutter figure of 0.022% WRMS.
The most distinctive feature of the Alpine AL-90 was its B.L.E.S. computerised calibration system. B.L.E.S. analysed the inserted cassette and automatically adjusted bias current, Dolby level and equalisation to establish recording conditions for the tape. Alpine described the process as selecting from more than eight million possible combinations of adjustment values.
After B.L.E.S. was activated, the Alpine AL-90 recorded brief test signals at 1kHz, 7kHz and 15kHz using its internal oscillator. The deck then analysed the recorded signals through the three-head monitoring system and adjusted bias, recording level and equalisation in steps as small as 0.25dB. The process was repeated until the response at all three test frequencies met the calibration requirements.
When calibration was completed successfully, an OK indicator illuminated. If the tape could not be calibrated within the required tolerances, or if the tape formulation did not match the selected tape position, an error indicator warned the operator to change the tape or correct the selector setting. Calibration typically took between 20 and 40 seconds.
The B.L.E.S. system sought to establish frequency response within ±1dB at 1kHz and 7kHz, and within ±3dB at 15kHz. Four sets of calibration data could be stored, one for each tape selector position, and recalled when the same cassette type was used again. Standard factory calibration settings were also retained for the four supported tape formulations.
A manual bias fine control allowed the automated B.L.E.S. result to be altered when required. Increasing the bias could reduce distortion, although with some loss of high-frequency response, while reducing the bias could extend the high-frequency response at the expense of increased distortion.
The recording and playback amplifier circuits of the Alpine AL-90 used separate power supplies for the two channels to reduce channel interaction and dynamic distortion. High-gain, low-noise dual-gate FETs were used in the amplification stages, while the playback head was directly coupled to the playback equaliser amplifier without a coupling capacitor.
The Alpine AL-90 included a switchable MPX filter. With the filter removed from the signal path, the amplifier circuitry provided response extending to 60kHz. Connection terminals were also provided for an external noise-reduction processor. After processing, the signal returned through the line amplifier, meter amplifier and headphone amplifier, allowing the result to be checked on the meters and through headphones.
Recording levels on the Alpine AL-90 were displayed by professional-grade meters switchable between peak and average VU indication. Their scales extended from -40dB to +10dB. Separate controls were provided for the master recording level, line input and microphone input, allowing microphone and line sources to be mixed. The deck also provided output-level adjustment.
A four-digit multi-memory tape and time counter was provided with auto-play and auto-rewind functions. Pitch control allowed tape speed to be varied by up to ±6%, corresponding to approximately one semitone. Additional operating facilities included cue and review, Auto Space, timer-assisted recording and playback, a headphone output, microphone inputs and optional remote control.
A microphone connected to the left-channel input could be recorded to both stereo channels using the microphone mono facility. An optional rack-mounting kit allowed the Alpine AL-90 to be installed in a standard 19-inch EIA equipment rack.
Features
- Three-head Sendust and ferrite head system
- Separate recording, playback and erase heads
- Professional tape and source monitoring
- Three-motor transport
- Direct-drive closed-loop dual-capstan mechanism
- Computer-controlled transport functions
- Feather-touch sensor controls
- Automatic tape-slack removal
- Computerised B.L.E.S. cassette calibration
- Automatic bias, recording-level and equalisation adjustment
- Internal 1kHz, 7kHz and 15kHz test oscillator
- Four calibration memories
- Manual bias fine adjustment
- Dolby B noise reduction
- Dolby C noise reduction
- Switchable Peak/VU level meters
- Separate master, line and microphone recording-level controls
- Direct-coupled amplifier circuitry
- Separate channel power supplies
- FET-equipped amplification stages
- Defeatable MPX filter
- Connections for an external noise-reduction processor
- Four-digit multi-memory tape and time counter
- Auto-play and auto-rewind
- Pitch control with a ±6% adjustment range
- Cue and review functions
- Auto Space function
- Timer-assisted recording and playback
- Microphone mono recording facility
- Optional remote-control unit
- Optional rack-mounting kit