Akai GX-400D-SS
A 31.2-kilogram quadraphonic open-reel deck that Akai built off its professional GX-400Dpro mechanism. Period reviewers trusted it enough to recommend it for serious four-channel work.
Overview
At 31.2 kg, the GX-400D-SS is not a deck you move on a whim. It was priced at ¥345,000 in Japan around 1975, and Akai developed it using the mechanism of its pro-oriented GX-400Dpro — a lineage that shows in the way the transport is put together. This is a four-channel open-reel tape deck, not a cassette deck, despite what the "D" suffix and a few mislabeled eBay listings might suggest. The machine handles 10½-inch reels and runs at three speeds, and its four-track system can be switched between four-channel and two-channel stereo recording and playback. Akai's Quadra Sync mechanism made multi-channel dubbing possible, which is the whole point of a deck like this: you don't buy a 400D-SS to play back stereo tapes, you buy it to move four channels around without generational collapse.
The system also has auto-reverse playback and sound-on-sound recording. It carries four heads: one GX 4ch/2ch recording head, one GX 4ch/2ch playback head, and one each rear-channel and front-channel erase head. A 1979 classified ad in Audio (July 1979, p.112) describes a used example as a 4-channel deck with three speeds and remote outboard Dolby. So the noise reduction sat outside the chassis rather than inside it.
Key Features
Quadra Sync and 4-Channel / 2-Channel Switching
The defining feature is the mode selector, which converts the deck between four-channel surround-stereo operation and conventional two-channel stereo. Combined with Akai's Quadra Sync mechanism, this made multi-channel dubbing practical. The unit's four-track system is the hardware foundation: one transport, two ways to use it.
GX Glass-and-Crystal Ferrite Heads
The deck carries GX heads, Akai's glass-and-crystal-ferrite design, a technology the company patented in 1969. The point of the GX construction is wear resistance and stable high-frequency response over time. Audio (February 1975, p.48) judged the capstan assembly, heads, and tape guides to be up to professional standards.
Signal-Level-Dependent High-Frequency Circuit
Akai fitted the 400D-SS with a circuit that adjusts according to signal level to improve response above 8 kHz at the slower tape speeds. Audio (February 1975, p.48) described it as achieving results somewhat similar to the Dolby and ANRS noise-reduction systems, and suggested it likely accounted for the strong signal-to-noise figures the magazine measured at slow speed. The slower speeds are where most decks get muddy up top, and this circuit was aimed at that.
Panel, Meters, and Recording Indicators
The front panel is black and satin, with contrasting blue meters and colored pushbuttons. Audio (February 1975, p.48) commented on the look favorably. Above each meter sits a per-track indicator lamp that lights when that track is recording. That is handy on a four-channel machine, where it's easy to lose track of which channel is armed. Modern-Recording (August 1976, p.63) noted those lamps in its write-up.
Tape Selector — and Its Documentation Problem
The tape-selector switch offers positions for low-noise tape and "wide-range" tape, the latter defined only as "a grade higher than low-noise." Modern-Recording (August 1976, p.63) called the labeling needlessly cryptic, noting that Akai never spelled out whether "wide-range" meant chrome, ferrichrome, or something else. The recommended standard tape for the machine was low-noise.
Meter Ballistics and Rewind Speed
HiFI-Stereo (April 1975, p.48) found the meter movement slower than true VU standards. The needles reached only about 65 percent of their steady-state reading, which makes precise level-setting trickier. The same review clocked a full-reel rewind at roughly 95 seconds.
Historical Context
The GX-400D-SS sits in a family that includes the GX-400D and the pro-oriented GX-400Dpro. The three share at least some parts - an insulating liner for the right side, MPN MZ534958, is listed as fitting all three. Akai's GX head technology, which underpins the whole line, dates to a 1969 patent. The 400D-SS was priced at ¥345,000 in Japan around 1975, which places it in the top tier of Akai's consumer reel-to-reel lineup for the period. One Russian-language source groups the D, D-Pro, and D-SS together and associates the family with the Soviet Elf 001. That connection is stated without detail and should be treated as a curiosity rather than a documented lineage.
Collectibility & Value
These decks have a specific, well-known failure point: a nylon piece inside the right tension arm. One owner reported a unit sitting dormant since 1998 for exactly that reason, and noted the part was unavailable when they went looking for it. Check that before buying. Parts do circulate on the secondary market, including right take-up motors, right tension arms, insulating liners, lamp light board assemblies, complete head assemblies with harness, headstacks, and front panels with head covers. A right tension arm alone has been listed at US $120.00 (approximately EUR 105.36). Service manuals turn up as well, and accessories like lubricant kits and operator's manuals sell for under $20. Restored, functional examples do surface, but the market is thin enough that condition and completeness matter far more than any published price guide.
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