Ultimate series of recorders which sold extremely well because they were very good.
Also, because Technics advertised about them at length. And also because they do look as good as they do sound ;-)
Most common is the RS-1500U original version which was named, or nicknamed, U38 in Japan, the U being the shape the tape takes when wrapped around the head-block and capstan, but Technics made quite a few variants, all in 3-speed flavor :
RS-1500U (2T with 4T play)
RS-1506U (4T with 2T play)
RS-1520U (2T with 4T play and
added eq/bias/oscillator panel)
RS-1700U (4T auto-reverse)
RS-1700US (same as above but silver)
RS-1800U (76cm/s studio monster)
RS-777 (later silver cutie).
All share the same enormous DD motors, Isoloop tape path and basic functions ; the differences lie in the available speeds, the built-in preamps and features.
All of these versions are (or will be) individually posted here on TVK.
Bar the RS-1800, none of these versions was expressly built as a professional machine although the 1520 did find its way into some audiophile-oriented places.
Despite Matsushita's enormous industrial power, Technics never managed to really find its spot in the broadcast industry throughout the 1970s but for one item - the famed SP-10 turntable.
All of Technics' efforts on recorders, analogue or digital, and loudspeakers remained to no avail : digital would be Sony, loudspeakers were TAD, Tannoy and sometimes JBL and recorders were either Studer, Otari or Ampex and later on Sony.
These brands had only one thing in common : compared to the Matushita empire, they were each of microscopic dimensions ! Big isn't always better.
The RS-1500U is a 3-DD motor 1/4" recorder with a tape path completely different than all of the other offerings available then : the tape makes a complete U-turn around a reversing roller. Guides and rollers are therefore all gathered atop the head-block, in between the reels ; the 3,4cm capstan itself is located between the two pinch-rollers, just before the head-block.
This arrangement with the two tension-rollers placed atop the narrow loop offers an excellent immunity regarding the influence of the reels on the tape's tension : Isoloop stands for Isolated Loop after all. The tension accumulated within the loop is of 80g.
The heads are located on either side of the head-block, doubled-up for the RS-1700U and RS-777 auto-reverse models, and the head-block of the 2T models has a switch allowing it to read 4T tapes (and vice-versa for the RS-1506).
The three motors are brushless direct-drive big guns which take 0,7s to reach their 38cm/s speed - lots of torque.
The capstan motor is Quartz-regulated with a PLL loop voltage+phase-comparing the motor's speed.
Onboard electronics were designed accordingly to the high-quality of the transport : FET inputs, low-noise and DC MIC circuits and SEPP rec amplifier with linearity maintained up to +25dB above the 0 VU (at 1Khz) .
Features are more common and consist of what everybody else had as well : pitch control, timer switch, MIC attenuators, meter scale switch, EQ/Bias selectors, and a mechanical counter which can indicate real-time time when used at 38cm/s.
The one and only problem of thee RS-1500 series, and of most of Technics' output between 1976 and 1978, is... color.
No beautifuly anodized aluminium here but cheap, boring, matte brown-ish paint which by definition sucks light and doesn't "play" with it, ages fast and always looks unclean.
Also many plastic visual parts, unwelcome in such a pricey object.
Technics clearly saved bucks on this and that is a real shame because some of the parts were magnificently designed : the RS-1700 transport keys, the IsoLoop of course or the triple-concentric big knobs.
Nevertheless, again, after the later introduction of the RS-1800 and a PCM version of the latter, the series was augmented with the extra-rare RS-777 cutie, a 7" 4-Track auto-reverse, which was a beautiful bye bye to a market Technics never did really try to take over.
The Isoloop wasn't a true novelty as Sony, Teac and others had used it in numerous video, audio and mostly data open-reel recorders (the 76cm/s Sony DRF-3430 for instance) years before 1976, but in the hi-fi world it was first... and a last.
With it, Technics managed to make one of the most desirable series of recorders ever with its first serious attempt and without being known as a "tape specialist" like Sony, Teac or Akai were, too.
A "coup de maître" if you will.
Although this page is already quite compleat (in Knobber version that is), I still have many many beautiful images waiting to be scanned !
Splendid nudies aplenty here.
An AUDIO (US) review can be downloaded in .pdf here (scroll down to lower part of the page).