Released in 1977, the Technics RS-7500US was a high-fidelity stereo ELCASET recorder designed to combine the straightforward handling of a cassette deck with performance characteristics closer to those of an open-reel tape recorder. ELCASET had been developed by a consortium of Japanese audio manufacturers as a larger cassette-based recording format using 6.3mm tape, the same width commonly employed by open-reel machines. Operating at 9.5cm/s, twice the speed of a conventional compact cassette, the format provided increased tape area, a wider frequency response and greater dynamic range while retaining an enclosed and easily handled tape cartridge.
The Technics RS-7500US was built around a true three-head configuration consisting of separate Super Permalloy recording and playback heads together with a double-gap ferrite erase head. Unlike combined record and playback head arrangements, the independent heads allowed each component to be optimised for its particular function. The recording head used a 10µm gap intended to minimise distortion across a broad frequency range, while the playback head employed a 2µm gap to improve output at higher frequencies. The double-gap erase head provided complete erasure across the supported ELCASET tape formulations.
The separate recording and playback heads also enabled immediate off-tape monitoring while a recording was being made. A tape/source monitor selector allowed the incoming signal to be compared directly with the recorded result, while an indicator lamp showed when source monitoring was selected. The head arrangement also permitted adjustment of playback head azimuth and gave the operator direct confirmation of recording performance.
With Type II and Type III tape, the Technics RS-7500US provided a stated frequency response of 25Hz to 22kHz within ±3dB, extending to 20Hz to 25kHz when measured to the DIN standard. Type I tape provided a frequency response of 25Hz to 20kHz within ±3dB. The wider tape and increased operating speed also raised the available high-frequency maximum output level compared with conventional compact cassette recording.
Tape transport was driven by a frequency-generator servo-controlled DC motor. The electronically regulated system maintained accurate capstan speed during changes in supply voltage, load torque and ambient temperature. A 4mm capstan was coupled to a balanced, high-inertia flywheel to stabilise tape movement and reduce speed variation. The transport achieved a quoted wow and flutter figure of 0.06% WRMS or ±0.15% DIN.
The ELCASET mechanism lifted the tape from its cartridge and positioned it against the stationary heads, capstan and tape guides. This arrangement reduced the number of moving transport components and helped control modulation noise, crosstalk and tape alignment. An independent reel-drive arrangement isolated take-up reel torque from the capstan system, while torque limiters on the supply and take-up reels reduced tape strain during rapid winding and stopping.
A photo-electronic automatic stop system used the transparent leader fitted at each end of an ELCASET tape. An LED and photosensitive transistor detected the leader and brought the transport to a controlled stop. The system operated during normal playback, recording, fast forward and rewind, protecting both the tape and the transport mechanism from unnecessary mechanical stress.
The Technics RS-7500US automatically identified the three available ELCASET formulations. Sensor wells along the rear edge of the cartridge allowed the machine to recognise Type I normal, Type II ferri-chrome and Type III chromium dioxide tape. The corresponding bias and equalisation circuits were selected electronically, with front-panel lamps indicating the detected formulation. Transistor switching was used in place of mechanical contacts to reduce switching noise and connection problems.
The recording electronics included separate microphone and line-input amplifier stages. The microphone circuit used a two-stage, direct-coupled NPN and PNP transistor configuration supplied from a constant-voltage dual power supply. Its output was mixed with the line input through a high-input-impedance operational amplifier incorporating FET devices. This arrangement allowed microphone and line levels to be adjusted independently while limiting interaction between the two signal paths.
Separate amplifiers were provided for microphone input, line input, recording and playback. Low-noise transistors, FETs and precision resistors were employed throughout the signal path. A six-transistor constant-voltage circuit supplied the amplifier stages, while the playback amplifier used a dual power supply. An eleven-transistor electronic muting circuit suppressed switching noises when power was applied or removed and when recording began or ended.
Recording levels were displayed through two large illuminated VU meters. Their full-range scales and response mechanisms were intended to provide accurate level setting while taking advantage of the increased dynamic range offered by ELCASET tape. Separate controls were provided for left and right input levels, together with a master output-level control that allowed the recorder’s playback output to be matched with other components connected to the same amplifier or receiver.
A memory rewind function allowed the operator to mark a tape position by resetting the mechanical counter to 000 and activating the memory control. The machine would then return automatically to that location during rewind. Low-noise switching transistors were employed in the memory circuit to prevent switching noise from entering the audio system.
Timer-controlled recording and playback were also supported when the Technics RS-7500US was connected to a suitable external timer. A solenoid released the pause mechanism when power was applied, while an electronic muting delay held the selected recording or playback mode for the first few seconds as the amplifier circuits reached operating condition.
Loading and unloading were handled through a mechanically assisted tape compartment. Closing the door caused the tape to be raised from the ELCASET cartridge and placed into operating position. Pressing eject returned the tape smoothly to its cartridge before the silicon oil-damped door opened. A transparent removable head cover allowed the tape path and head area to be inspected without dismantling the recorder and could be removed for cleaning and routine maintenance.
The ELCASET cartridge included reversible slide controls for erase prevention, removing the need to break permanent plastic tabs from the cartridge. Its enlarged viewing window, combined with internal illumination from behind the tape, provided a clear indication of the amount of tape remaining on each reel.
The Technics RS-7500US recorded both stereo channels as adjacent tracks on the same side of the tape, maintaining stereo and mono compatibility in a manner similar to compact cassette recording. Rear-panel connections included separate line inputs and outputs together with a five-pin DIN recording and playback connector. Three front-panel headphone sockets were provided for stereo, left-channel and right-channel monitoring.
The Technics RS-7500US represented Technics’ implementation of the ELCASET system as a substantial home recording deck with automated tape selection, protected tape handling, electronic transport functions and separate recording and playback heads. Although ELCASET was ultimately short-lived as a commercial format, the RS-7500US demonstrated the level of engineering applied to the attempt to combine open-reel tape performance with cartridge-based operation.
Features
- True three-head recording system with separate record, playback and erase heads
- Super Permalloy recording and playback heads
- Double-gap ferrite erase head
- Direct off-tape monitoring during recording
- Automatic identification of Type I, Type II and Type III ELCASET tape
- Automatic electronic bias and equalisation selection
- Frequency-generator servo-controlled DC motor
- High-inertia flywheel and 4mm capstan
- Independent reel-drive system
- Photo-electronic full automatic stop
- Supply and take-up reel torque limiters
- Separate microphone and line-input amplifiers
- Microphone and line-input mixing
- Separate left and right recording-level controls
- Large illuminated VU meters
- Tape and source monitoring selector
- Memory rewind with three-digit tape counter
- External timer recording and playback capability
- Electronic muting during power and transport switching
- Mechanically assisted tape loading and unloading
- Silicon oil-damped tape compartment door
- Illuminated tape window
- Transparent removable head cover
- Adjustable output level
- Reversible cartridge erase-prevention controls
- Stereo and mono compatible track arrangement
- Line, DIN and headphone connections