Operating instructions

1.1 The Otari MTR-90III Tape Recorder
The Otari MTR-90III records and reproduces 1" or 2" master tapes in an
8-track, 16-track or 24-track format according to the head assembly and the
number of Audio PCB Assemblies. Tension is distributed uniformly across
the tape surface by a pair of wide diameter pinchrollerless spindles, the
capstan and the tachometer. This design eliminates contact between the tape
drive and the oxide, allowing virtually unlimited safe passes of valuable
master tapes. Mechanical integrity and long-term stability are ensured by a
massive, precision top plate and a unitized, welded steel chassis. The newly
designed High Speed Motor Drive Amplifier features self protection and reel-
end deceleration for better tape manipulation and more efficient editing.
Ultra-high torque DC servo reel motors provide fast winding even with 14"
reels, and ensure rapid start-ups to full stable record/play speed. The entire
machine is modular in construction, including the computerized transport
control logic, for high reliability and serviceability.
The MTR-90III is loaded with convenient features such selection of external
speed reference, vari-speed, or 2 crystal-locked speeds—15/30 ips (38/76
cm/s) or 7.5/15 ips (19/38 cm/s). The reels can be gently rocked back and
forth for editing with the easy-to-use Cue Wheel or by hand turning the
capstan. Push buttons also provide for tension release and retraction of the
motor-driven head shields to expedite editing. A practical splicing block and
a spot erase function for erasure of unwanted tracks are also provided in
front of the head assembly.
The electronics are highly refined. A single PCB Assembly approach has
been used for the RECORD/PLAY AUDIO and BIAS PCB Assemblies for each
channel simplifying setup and service. Active mixing of audio and bias in the
record circuitry, proper utilization of high slew rate IC op-amps, and discrete
components at critical stages ensure the cleanest and quietest recordings.
There are, of course, individual channel calibrations for bias, low and high
speed EQ and gain, and a low and high speed record PHASE COMP trimmer
for improving complex waveform characteristics. In addition, a 3 position
Master BIAS SELECT switch (with 3 corresponding trimmers) enables the
entire machine, once aligned, to be rapidly switched to accommodate the
bias requirements of different tapes. For further convenience, a single test
input jack applies test/alignment signal to all inputs. There is automatic
switching between sync reproduce and input monitor when the machine is
switched between play and stop, fast winding modes, and of course
Rec/Ready to record enable. Dip switches on the TRANSPORT CONTROL
PCB Assembly permit these logic functions to be changed to suit the
preference of the user.
Stable ACTIVE BALANCE Circuitry has been used in the input circuit. In the
output circuit, balanced or unbalanced operation can be selected.
(Transformer output or input may be ordered separately.) In addition, a
SERIAL I/O CONNECTOR, conforming to the RS232 standard for direct
conversation with a computer, and an Otari Standard Parallel I/O Interface are
provided for extended external control.
The model CB-147 Remote Control Unit is included as standard equipment.
It features the same transport control buttons as the MTR-90III and provides
individual function selections for each channel (Repro/Sel·Rep/Input), master
function selections for all channels at once (All Inputs/All Sel·Rep/All Repro),
and a master "All Safe" function. Also located on the Remote Control Unit are
a Speed Reference Selector switch (VARI, FIX, EXT), a Pitch Control knob,
and a Digital Readout indicating speed in percentage or inches per second
(ips).
Section 1 Introduction
1 - 2
October 1990
MTR-90III Operation and Maintenance Manual