Техническое объяснение терминологии  фирмы JVC 1979-1984

DD (Direct Drive) Mechanism Equipped with Newly Developed Quartz-locked Pulse Servo DD Motor

A direct drive system is employed in which the motor shaft itself is the capstan shaft, without the rotation transmitting members ( idlers, pulleys, etc.) which cause unstable tape rotation . Our newly developed pulse servo motor is employed fot the driving power source . 

The motor,s construction is free from thrust unbalance or cogging, thus permitting a high flywheel effect . For precise rotation , this motor uses a full-circumference integration type FG detection sysytem and an autobalance circuit which reduces torque unbalance , Thus the motor drives the tape transport mechanism with smooyh rotation. Further, the employment of the quartz lock system results inexceedingly small flucuation of speed.

it concern DD-7, DD-9 

Three-head System with X-cut SA Record-Playback Combination Head.

The record head uses a 4u-gap SA head for improved recording sensivity and a reduced distortion rate. The playback head an X-cut 1u-gap SA head for reduced low-frequency contour effect. These two heads are combined .The erase head employs a 2-gap SA head excellent in  erasure efficiency. 

B.E.S.T. ( bias. equalizer. sensitivity tuning) System 3-head tape deck.

This system was developed for 3-head tape deck utilizing the concept of previous versions KD-A8, KD-A66.

With stress laid upon MOL balance, the bias level is set at average of the optimum bias point which are detected at 16 steps each for R and L chanels .

To control the medium-frequency responce , a process o make the 4 KHz.1kHZ responce flat is provided .This responce is set at the average between those R and L values which are taken each at 8 steps.

The tape sensitivity is set at an average of those R and L values which are taken 16 steps each. The higj frequency equalization level is adjusted at 16 steps each for R and L channels , independently.