The GX-400D/GX-400D-PRO has been available in three different versions: a 2-track version (PRO) a 4-track auto-reverse version and a 4-track, 4 channel version (SS). Apparently there is also a version of the GX-400D-PRO which has a linear (slide ) control on the audio section. This set is in two separate pieces like the PRO-1000, and is even a bit larger in size.
All the 400D sets and the PRO-1000 can handle 10.5" reels and use a rather hefty servo-controlled capstan motor which drives two large flywheels each has a thick capstan at its center, so its is a dual capstan system, via a 30 inch belt.
The 1/4 Track version has 2 playback heads and two combination heads (Akai called them "combo" heads) so you could record in both forward and reverse mode. There are three speeds: 9.5 cm/s, 19 cm/s and 38 cm/s, an auto shut off function (except for the PRO version), it's capable to make sound-on-sound recordings and both versions have a tape cueing switch. All sets have some facilities to mix the line, DIN and mic (2x) signals.
The 2 Track Stereo (PRO) version has an APF button instead of a reverse button. A.P.F. stands for Auto Program Finder. Here the Automatic Program Finder, with the simple application of sensing foil to the magnetic tape facilitates automatic rewind and/or rewind and playback. For Automatic Rewind: Affixing a piece of sensing foil to the outside of the magnetic tape at the place at which you wish to start to rewind the tape, with the A.P.F. Switch ON, the machine will automatically rewind.
Automatic rewind can be effected during playback or recording mode as the sensing foil passes the sensing pole. Automatic Playback: For automatic playback from rewind or automatic rewind mode, the application of another piece of sensing foil to the other side of the tape at the place from which you wish to playback the tape, with the A.P.F. Switch ON, the machine automatically returns to Playback mode when it hits the other foil strip.
Thus the GX-400D-PRO automatic rewind and playback functions when utilized simultaneously, provides a continuous rewind and playback between two points on a reel of tape. This is nearly identical to the Digital Counter Function of "Auto-Repeat" on the GX-625, which is much simpler and much more easily resettable, by depressing a pair of buttons.
The PRO version also has an additional 4 track Playback head. The 400-series have not been continued after the GX-400; the GX-600D was the next Akai set to handle the large 10.5" reels. The GX-400D though is a much sought after set because of its professional appearance, features and performance. It was superseded by the GX-650D.
The GX-400D is already shown on the front cover of the summer edition of a German 1973 Akai magazine but isn't described inside anywhere. However, it surely IS on the pricelist.
Track system: 4-track, 2 channel stereo system (2-track, 2 channel stereo system for PRO version)
Tape speed: 3.75 ips, 7.5 ips and 15 ips.
Total Wow and Flutter: Less than 0.035% @ 15 ips
Frequency response: 20 to 29,000 Hz +/- 3 dB @ 15.0 ips 20 to 27,000 Hz +/- 3 dB @ 7.5 ips 30 to 20,000 Hz +/- 3 dB @ 3.75 ips
S/N ratio: Better than 57 dB @ +3 dB and better than 58 dB (GX-400D-PRO)
FFWD/RWD time: 100 seconds for 2400' tape @ 60 Hz.
Main motor: SCM3-16TW 4 Pole Eddy Current AC Servo Motor
Reel motors: IMI-24TW 6 Pole Eddy Current inner rotor motors
Erase Head: RE4-6 ( Combo head x2 )
Recording head: RE4-6 ( Combo head x2 )
Playback head: P4-220 ( x2 )
Dimensions: 590 (H) x 457 (W) x 240 (D) mm.
Weight: 31.2 kg.
Power consumption: 160 W. max.
Listed new: $ 1880.00 for GX-400D in 1973 and $ 1835.00 for GX-400DPRO in 1973