The 4 Channel sets were an interesting new format for 1/4" tape, similar to a studio deck, it features more than two stereo tracks at one time. All of these sets are considered "Surround Sound" units, which is why their model designations all have the suffix -ss. Some also function as 2 Channel Stereo decks for both playback and recording, these also feature auto-reverse in Play capabilities. Most are later 1970's / early 1980's, and feature the GX Heads, but some are early Crossfield units, and some are non-GX Head versions of the some of the GX Head Sets. All are 7" reels decks, except for the last two the GX-400D-ss and the GX-630D-ss. which are 10.5" reel capable.
Surround-Sound is another way of describing the discrete 4 Channel "Quad" which was much touted in the late 1970's. Much like the GX-280D-ss and GX-297D-ss, the 4 Channel "Surround Sound" GX-630D-ss can record and play both normal 2 channel stereo as well as Record and Play 4 Channel discrete tapes ( but only in one direction they are still using the normal 1/4 track format on 1/4" tape, simply four at a time. The GX-630D-ss set also has the added capability of Quadra-Sync, which allows laying down one track while play another, synchronized. Normally if one was attempting to do this, it would introduce a time delay lag, which is based upon the time it takes the tape to travel between the record head and the playback head. The Quadra-Sync switches, reprogram the wiring, so one channel of the record head functions as a Playback head, at the same time that another channel of the Record head is operating in Record. This capability was missing from the earlier GX-280D-ss or GX-297D-ss Surround Sound sets, which can be disappointing, when one discovers what those sets cannot do.
Both the GX-400D-ss and the GX-630D-ss have one other thing in common,
that the Pinch Roller moves down to engage, so it contacts the oxide side of
the tape, and gets dirtier faster. The Dual Capstans present on the GX-400D
are Belt Driven:
Chronologically, the X-1800D-ss is the earliest Quad set, which also has an 8 Track built-in the side.
Next came the 1730D-ss, which was a throwback to the mechanical operation block found on many lower-end sets, in the M Series, 1700 line, and 4000 Series. Like most other Akai 4 channel sets, it uses the Sanyo LD-3141 IC in its four channels of playback pre-amplifiers, actually it uses 8 of them in there, and for some reason, these parts were very prone to fail. So I guess the 1730D-ss is more prone to electronics failure than other sets that used fewer of those parts.
The 202D-ss is a rarely seen set, not that much that I can say about it. Being based upon the GX-210D which was a low-end three motor mechanism, it retains the two knob operational control mechanism, with all of the wheelies, rubber rollers, springs, cams, friction cams and other ensuing mechanical linkages. It also has two directional arrows switches, allowing it to perform auto-reverse, in two channel stereo mode. Since it has a 4 Channel Playback Head, it lacks the GX-210D's classic moving head mechanism. Its perhaps one level higher than the 1730D-ss, and a bit below most of the three motor Quad decks which don't have the mechanical linkages. It is probably pretty heavy, as the GX-210D seemed to be quite a heavy set, being of an early to mid-1970's vintage.
Here is the GX-280D-ss:
There is no method to Simult-Syncing, ( or Quadra-Sync, as Akai call the capability to lay down one track synchronized to the others without erasing any of the prior tracks, a capability which is only found in the GX-270D-ss, GX-630D-ss, and the GX-400D-ss ). When recording in 4 channel mode the full-track erase head erases all four tracks at once. In playback, of 1/4 track 2 channel, they will auto- reverse upon contact with foil tape placed at the end of the reel. There is no recording in reverse mode. If anyone knows of any differences between the GX-280D-ss and the GX-297D-Dss, please email me with the details!!!
Here is the GX-297D-ss:
In some ways what comes next - is the best. The GX-400D-ss, the 4 Channel Surround-Sound version, one of three model variations comprising all the sets found in the GX-400 line, the only significant variations found are sets where the VU Meters have a Blue or Yellow background, and knobs tinged with silver or gold colored plating. This is one heavy set, perhaps the heaviest later unit Akai made. It will play four channel quad tapes and rewind back to the beginning and start to play it over again, if foil tape is put in the appropriate places at both ends of the tape. Or it will auto-reverse in 2 Channel stereo mode, but only in Play. In record, it will stop and then Play the reverse side, tracks 2/4. Since the 4 channel GX Playback Head is simply in the wrong position for monitoring off the tape in the 2 Channel Reverse direction, Akai did not design it for Reverse Recording. Tape erasure is done here by two separate 2 channel erase heads, and I wonder if crosstalk was found to be a problem ? Or why else wouldn't they use a 4 channel Erase Head for that task ? In which case, the second erase head position theoretically could have then been replaced by a 2 channel Playback Head, and then Reverse Recording would have been possible in 2 Channel mode, with perhaps one more relay added to the circuitry. I guess it was simply too expensive to do that, this set was already a wallet hurting $1495. without the optional remote control box.
Its big, its heavy, and it consumes a rated 150 Watt of power, that's a bit more juice than just about any other Akai. It also has an interesting servo-controlled capstan motor, I think its one not seen in any other set. It is not the big bulky motors seen just two years prior in the GX-365D / GX-280D / GX-370D with the external servo-head, but a medium smaller unit with a diecast frame, much like the reel motors present in this set, which also are not the usual Akai outer rotor type. Also interesting is the fact that the GX-400's Servo-System uses TO-3 style transistors, unlike all the later sets which use less reliable plastic cased flat-pack transistors.
In an overkill of design work, like wearing a belt and suspenders, the capstan motor powers a thick and wide belt, which then drives dual capstan flywheels on which the precision balanced capstans are mounted. The Capstan Motor is also has three speeds, unlike those few other Akai's which need an additional capstan sleeve and smaller pinch roller for 15 ips operation, this set does that with a third position on the speed switch. Despite being an early technology, it is truly a combination of innovative design, and craftsmanship, resulting in near professional capabilities. This set while a high-end "QUAD" deck, has perhaps the lowest wow and flutter of any set seen outside of a recording studio.
The GX-400D-ss also features the Quadra-Sync System, where the Record
Head can be inserted into the Playback path in one or more channels, to
"time sync" newly recorded material, with a track recorded earlier. This
allows one to "bounce tracks" back and forth and to harmonize exactly,
with previously recorded material, with little or no loss of fidelity
because the Record Head in this case, is quite nearly as perfect as the
Playback Head in this application. Quite literally a recoding studio
in a huge wood box... with a frequency response that is basically flat to
30Khz. and more, with minimally low wow and flutter, the GX-400D-ss can
make near studio level tapes with low distortion, possibly even besting
the later GX-646 and GX-747 sets which nevertheless, were never made
available in a 4 channel version, and didn't have the 15 ips speed. Also
note that the GX-400D-ss and the GX-630D-ss are the only two Quad sets
which have the capstans below the Pinch Rollers, I suspect this design
difference denotes a significant line has been crossed between what could
be called the "consumer" units and the "Semi-Professional" Level, at
least in terms of being designed to run and function on a 24/7 level.
Here is the GX-400D-ss sitting with its companion RC-17 wired remote
box in front: