The 4 Track is the only American Mellotron ; it was an attempt to improve the M400.
Only 4 units were produced by Bomar Fabricators in Southbury, in 1981 : two of them were white, one was black and one was matt blue.
The 4 Track used 1/4" tapes with 4 tracks, as the name indicates.
Instead of using a block with 35 magnetic heads moving to select the desired track (as on the M400), the 4 Track used a block of fixed heads which were able to play 4 tracks at once.
Each track had its own preamp, with the following controls : 3 band EQ, pan, volume, on / off switch, and one "on" light.
The 4 Track had a pitch control, a new motor controller card (SMS-3) and seven audio outputs : 4 direct ones (one for each track), 2 stereo ones (left and right) and one mono output (master).
The cabinet was made of aluminium.
Although the 4 Track brought many technical improvements compared to the M400, the quality of its tapes (which were recorded in the United States) was poor. As a consequence, this machine has never been used to its full effect.