Technics RS-1500US

A three-motor, direct-drive, isolated-loop open-reel deck that chased laboratory measurements - and, for once, caught them.

Overview

The number that stops you cold is 0.018% WRMS. That's the RS-1500US's wow-and-flutter figure at 15 ips, and bench engineers would want to check the calibration on it. Technics got there with an "Isolated Loop" transport: a 3.4 cm direct-drive capstan with a pinch wheel on either side, so the tape path is decoupled from reel-tension variation. The company's own literature holds tape tension to a reported 80 grams, and describes the resulting speed deviation of ±0.10% at 38 cm/s (15 ips) as one-tenth to one-fifth the deviation of "high-quality decks available in the past." That's advertising copy, so take the comparison with skepticism. The measured numbers are harder to wave away.

Three speeds are on tap - 38, 19, and 9.5 cm/s (15, 7-1/2, and 3-3/4 ips) - and wow and flutter gets worse as you slow down: 0.03% WRMS at 7-1/2, 0.06% at 3-3/4. Frequency response is quoted at 30-30,000 Hz ±3 dB at 15 ips, 20-25,000 Hz at 7-1/2, and 20-15,000 Hz at 3-3/4.

DB-Magazine (July 1977, p.36) opened its test report by asking the obvious question — "When is a tape deck professional?" — and then noted the RS-1500US is a three-speed, three-motor direct-drive machine that departs from the norm in ways both large and small, right down to its use of phono jack inputs and outputs. That's the honest framing: this is a consumer-priced deck wearing pro-deck engineering.

Three direct-drive motors do the work. The capstan runs a quartz-locked phase-locked DC brushless servo motor. The two reel tables get their own tension-controlled DC brushless direct-drive motors. Reel capacity runs from 13 cm to 26.5 cm (5" to 10-1/2") outside diameter, with automatic tension control across that range. Fast wind of a 762 m (2,500 ft) reel takes 150 seconds. Modern-Recording (February 1977, p.68) clocked a 3,600-foot 10-1/2-inch reel at 145 seconds and noted the near-constant tape speed during fast-wind modes, with none of the acceleration surge as the reel end approaches.

The head complement is four: record, erase, a two-track playback head, and a separate four-track two-channel playback head. A front-panel switch flips between the two playback heads instantly, and the whole head module is a plug-in type removable via three screws. Track format is 2-track, 2-channel record/play/erase with 4-track, 2-channel playback. That is the reverse of the sibling RS-1506US, which records and plays 4-track and plays back 2-track. The 1500US is the 2-track machine, the 1506US is the 4-track machine, and Technics sold them as a matched pair for studios that needed both.

The electronics back up the "professional control" claim. The mic amp is a three-stage direct-coupled design with low-noise silicon transistors in the first stage, delivering a quoted 55 dB dynamic margin at the rated -72 dB input - 75 dB total with the 20 dB mic attenuator engaged. Overload margin on the mic input is 55 dB (75 dB with attenuator), and applicable microphone impedance spans 200 ohms to 10 kilohms. The recording amplifier uses an SEPP output stage with linearity extending to +25 dB above 0 VU at 1 kHz, which Technics argues means the tape saturates before the amp does. The mixing amplifier uses an FET op-amp with a non-existent mixing loss, and changing the mic level control doesn't disturb the line-in level setting. Three-way bias and three-way equalization switches give nine combinations, with bias level at 90%, 100%, and 110% across the three positions and a 120 kHz recording bias frequency.

Line input sensitivity is 60 mV (-24 dB) into 150 kilohms, with infinite overload margin since the line input feeds the level control directly. Line outputs are two pairs of phono jacks, 0.55 V at 0 VU with the output control at "8," rising to 0.775 V or more at maximum, output impedance under 3 kilohms into a 22-kilohm load. Headphone output is 80 mV at 0.55 V line output into 8 ohms. Signal-to-noise is 60 dB NAB-weighted at 15 ips (57 dB on the RS-1506US), 60 dB at 7-1/2, and 58 dB at 3-3/4. Channel separation exceeds 50 dB. Erase ratio beats 65 dB. Distortion via tape at 400 Hz is under 2% at peak level and under 0.8% at 0 VU.

Tape speed rise time is 0.7 seconds to rated speed at 15 ips. The manual's point is that the deck doesn't hunt above and below speed before settling, so you don't get the smeared attack at the head of a recording that slower-stabilizing transports produce. Level fluctuation is quoted at a maximum of 0.2 dB at 20 kHz (0.5 dB on the RS-1506US). Pitch control spans ±6% in both record and playback. The advertising copy said ±5%, but the manual's ±6% is the one to trust.

Power is switchable AC 110/125/220/240 V at 50/60 Hz, or 24 V DC at 4.5 A with the optional RP-086 battery adaptor. Consumption is 120 W. The deck weighs 25 kg (55 lbs) and measures 45.6 × 44.6 × 25.8 cm (18" × 17-1/2" × 10-1/8"). A time counter is accurate to ±1% at 15 ips. Auto-stop senses end-of-tape via tension roller switches and, during running, stops within 3 seconds of an accidental tape stop.

The accessory list is long for a consumer deck: the RP-9110 dust cover (which can stay on during play or record), the RP-9100 carrying case, the RP-086 battery adaptor, RP-9130 shelf brackets for standard 19-inch rack mounting, RP-9690 remote control for all transport functions, RP-9120 wooden side panels, and the RP-10A 26.5 cm empty reel. Technics also sold RT-10B218 tape - 762 m (2,500 ft) back-coated on a 26.5 cm (10-1/2") reel - and the factory calibration reference is Scotch No. 207.

Modern-Recording (February 1977, p.66) filed a full report on the deck, describing it as an open-reel three-speed stereo recorder of "unusual mechanical design" — which, given what the transport is doing, is a fair one-line summary. The magazine's reviewers, Norman Eisenberg and Len Feldman, walked the tape path in detail: over the rollers, across two of the heads, around a large bottom roller, up the "U" past two more heads. High-Fidelity (October 1977, p.147) ran the advertising line about saving $5,500 against a professional counterpart, and the suggested retail was $1,500. HiFi-Stereo (September 1977, p.45) ran the same ad copy, so the $5,500 comparison is Technics' own claim, not an independent verdict.

That's a serious feature list, and it's the reason the 1500US turns up in working studios rather than just in collections. The Steve Sperry "Mult Shop" personal-use studio gear list, for instance, has the RS-1500US sitting alongside a Studer B67 as the stereo mastering pair.

The usual open-reel caveats apply. The transport is mechanically complex - three direct-drive motors, a quartz-locked servo capstan, tension-sensing reel motors - and parts for the servo and head assemblies are hard to come by. The plug-in head module is a real serviceability win, but replacement heads are the scarce item. The deck's weight and rack-mount option mean most surviving examples have lived in racks, which is generally good for them but bad for the wooden side panels. Prices have firmed considerably from the original $1,500, and complete units with the remote and dust cover command a premium.

What the RS-1500US represents is a moment when Technics decided to build a consumer open-reel deck to professional measurement standards and let the spec sheet do the arguing. The 0.018% wow-and-flutter figure is still the headline, but the transport design behind it — the isolated loop, the twin pinch rollers, the direct-drive reel motors holding tension constant from hub to hub — is what makes the number repeatable rather than a one-off bench fluke. It's not a Studer, and Technics never pretended it was. But it's a deck that made the professionals ask the question out loud.