Released in 1976, the Technics RS-1500 was a three-speed, two-channel open-reel tape recorder built around the company’s Isolated Loop tape transport system. The RS-1500US version provided two-track recording and playback together with four-track playback, allowing it to make professional two-track recordings while remaining compatible with four-track stereo tapes recorded on other machines. Its combination of a direct-drive transport, quartz-controlled capstan motor, professional editing facilities and comprehensive recording electronics placed it among Technics’ most advanced open-reel recorders.
At the centre of the Technics RS-1500 was its distinctive U-shaped Isolated Loop tape path. Instead of moving the tape through a conventional arrangement of guides, tension arms and separate capstan components, the RS-1500 used a single 34mm capstan, two pinch rollers and a reversing roller to form a closed tape loop around the heads. The recording, playback and erase heads were positioned inside this loop, isolating the tape at the head assembly from disturbances caused by the supply and take-up reels.
Tape tension within the Isolated Loop was maintained at approximately 80g, around half that of a conventional transport system described by Technics at the time. The lower tension helped the tape maintain consistent contact with the heads while reducing the mechanical loading imposed on the tape and head assembly. The exposed arrangement also made the heads readily accessible for inspection and cleaning, while tape threading required no complicated routing around multiple guide posts and tension levers.
The Technics RS-1500 employed three direct-drive motors. Its capstan motor was a quartz-controlled, phase-locked, brushless DC servo design, while each reel table was driven by its own electronically commutated brushless DC motor. The capstan, flywheel and motor rotated as a single assembly without an intermediate belt or speed-reduction system. This eliminated drive belts from the capstan mechanism and reduced the number of mechanical components capable of introducing rotational instability.
A quartz oscillator operating at 4,194,304Hz supplied the reference frequency for the capstan servo system. A specially designed integrated circuit divided this frequency and compared it with a signal generated by the capstan motor. Both speed and phase differences were monitored, allowing the motor control system to make immediate corrections without waiting for a complete capstan revolution. This arrangement maintained the selected tape speed with a specified deviation of ±0.1% and a maximum speed fluctuation of 0.05% at 38cm/s.
Electronic torque control continuously regulated the two reel motors according to the amount of tape present on each reel. This maintained consistent tape tension as the supply reel emptied and the take-up reel filled. The high-torque transport reached its rated speed of 38cm/s within 0.7 seconds, while the Isolated Loop and direct-drive system produced a specified wow and flutter figure of 0.018% WRMS at the highest speed.
Three tape speeds were provided: 38cm/s, 19cm/s and 9.5cm/s. The speed could be changed through the electronic control circuitry without stopping the transport. A pitch control disengaged the quartz reference when required and permitted speed variation of up to ±6% during recording or playback. With the pitch control returned to its locked position, the quartz-controlled phase-locked system resumed control of the capstan.
The Technics RS-1500 head assembly contained four heads arranged in the direction of tape travel. These comprised a four-track playback head, two-track erase head, two-track recording head and two-track playback head. A front-mounted selector switched between the two-track and four-track playback heads. The removable plug-in head assembly also allowed conversion to an alternative configuration following installation and adjustment by a Technics service facility.
Recording electronics included separate microphone, line, recording and mixing amplifier circuits. The microphone amplifier used a three-stage direct-coupled circuit with low-noise silicon transistors in its first stage. It provided a 55dB overload margin at the rated microphone input, increased to 75dB when the switchable 20dB microphone attenuator was engaged. The attenuator allowed the recorder to accommodate high-output microphones and elevated sound pressure levels without overloading the microphone input stage.
The recording amplifier used a single-ended push-pull output circuit and maintained linearity to 25dB above the standard recording level at 1kHz. A field-effect transistor operational amplifier was incorporated into the mixing circuit, allowing microphone and line signals to be combined without the microphone level control changing the selected line input setting. Separate microphone and line recording controls were provided for the left and right channels, with indexing rings around the controls for marking and recalling settings.
Independent three-position bias and equalisation selectors provided nine possible combinations. These controls allowed the recording electronics to be matched to different tape formulations and operating speeds. The standard position used setting 2 for both bias and equalisation when recording on Technics RT-10B218 tape, equivalent to Scotch 207.
Two illuminated level meters operated during both recording and playback. A meter scale selector changed the indication between +3dB and +6dB ranges, providing additional scale capacity for programme material with elevated peaks. Independent tape and source monitor switches were fitted for each channel, allowing comparison of the incoming signal with the recorded result during recording.
The real-time tape counter displayed elapsed minutes and seconds when operating at 38cm/s. Unlike a conventional mechanical counter showing an arbitrary numerical position, the time display provided a direct indication of recorded duration. For editing, the cue control brought the tape into contact with the playback heads during fast forward or rewind, allowing a required section to be located audibly. Cueing could also be performed while rotating the reels manually.
An edit dial helped transfer the position heard at the playback head to the tape cutting position. After locating the edit point, turning the take-up reel until the dial completed half a revolution moved the selected section of tape to the position marker for cutting and splicing. These facilities complemented the two-track format, which was suited to physical tape editing and professional programme assembly.
Transport commands were controlled by integrated-circuit and transistor logic rather than mechanically linked function switches or relays. Direct mode changes could be made without first pressing stop. During most transitions, the logic system momentarily halted the tape before engaging the selected function, reducing unnecessary strain on the tape. Separate controls were provided for record, pause, rewind, stop, play and fast forward.
The Technics RS-1500 could accommodate reels from 130mm to 265mm in diameter. Fast winding time for 762m of tape was specified at 150 seconds. Automatic stopping was activated by the tension rollers at the end of the tape, while an additional protection system stopped the transport within three seconds if tape movement ceased unexpectedly during operation.
Connection facilities included independent microphone inputs, line inputs, parallel through outputs, two pairs of line output sockets and a stereo headphone output. The output level control adjusted both the line and headphone levels. With the control positioned at its reference mark, a meter reading of 0VU corresponded to a magnetic flux density of 185nWb/m.
The Technics RS-1500 could operate from 110V, 125V, 220V or 240V AC supplies at 50Hz or 60Hz. It could also operate from a 24V DC source using the optional RP-086 battery adaptor, enabling location recording where mains electricity was unavailable. Other optional accessories included the RP-9110 dust cover, RP-9100 carrying case, RP-9690 remote control unit, RP-9130 rack-mounting brackets, RP-9120 wooden side panels, RT-10B218 blank tape and RP-10A empty reel.
Features
- Two-track, two-channel recording and playback
- Four-track, two-channel playback compatibility
- Three direct-drive motors
- Quartz-controlled phase-locked capstan servo
- Technics Isolated Loop tape transport system
- Single 34mm capstan with two pinch rollers
- Electronically controlled reel tension
- Three tape speeds
- Pitch control with ±6% adjustment
- Plug-in four-head assembly
- Independent microphone and line recording controls
- Microphone and line signal mixing
- Switchable 20dB microphone attenuator
- Three-position bias selector
- Three-position equalisation selector
- Independent tape and source monitoring for each channel
- Selectable +3dB and +6dB meter scales
- Real-time minutes and seconds tape counter
- Cue monitoring during fast winding and manual reel movement
- Edit dial and tape position marker
- Integrated-circuit logic transport control
- Direct mode-to-mode transport switching
- Timer-controlled recording or playback start
- Automatic end-of-tape stopping
- AC or optional 24V DC operation
- Optional remote control, carrying case, dust cover, wooden side panels and rack brackets