Principles Of Operation; Introduction; Tape Drive Components - 3M Series 410 Instruction Manual

PRINCIPLES OF OPERATION
INTRODUCTION
The 3M Brand Professional Audio Tape Recorder is an advanced audio
recording instrument that incorporates the best techniques available at the present
state of the art. A tape recorder consists basically of a tape transport (deck) and
record and reproduce (play) electronics . The signal to be recorded is amplified
and applied to a magnetic record head, which impresses a magnetic pattern in the
oxide coating of the magnetic recording tape in accordance with the variation of the
input signal. During reproduction (play) the variations in magnetic flux that were
impressed on the tape during recording, are sensed by a reproduce head, amplified,
a nd applied to the rec orde r output.
In order to record and reproduce with a minimum of distortion, a high­
frequency bias is mixed with the input signal at the record head so that recording
takes place in the portion of the magnetization curve that is essentially linear.
The signal recovered by the reproduce head must also be equalized by circuits
that compensate for the response characteristics of the reproduce · head at low and
high frequencies.
The high-frequency signal that is used for bias is also used to erase signals
that may have previously been recorded on the tape. The erase signal is applied to
a separate erase head, which is similar to the record head but applies the high­
frequency signal at a much higher level. The signal applied to the erase head drives
the magnetic material of the tape to complete magnetic saturation to obliterate any
signal, or noise that may have been previously recorded on the tape.
The patented Isoloop tape drive maintains differentia 1 tension within the
loop of tape passing over the heads and ensures that the tape remains in close
contact with the heads during tape travel. This ensures that the magnetic flux
impressed by the record head penetrates the oxide material uniformly and eliminates
variations in amplitude that can result if the close head-to-tape contact is not
maintained. Similar amplitude variations can take place if the tape is not maintained
in close contact with the play head.
Tape Drive Components (S•• Figure 24)
Components of the tape drive system consist of a capstan drive motor, two
reel drive motors, and control relays tha t determine the mode of operation. When
in play and record modes, the tape is moved through the lsoloop by the capstan.
The reel drive motors maintain constant tension on the tape as it enters and leaves
the loop. When in fast-forward or rewind, tension is released within the Isoloop
and the reel drive motors move the tape through the loop independently of the
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