Ampex 351 - Page 46

17
Noise Balance
One of our greatest potential sources of noise is in
Demagnetization
If any of the components in our tape threading
path become permanently magnetized, we might par 
tially erase any high frequencies recorded on the tape.
If magnetization occurs at our magnetic heads we can
at least expect an increase in noise level. Some means
of demagnetizing these components must therefore
be available.
Braking Adjustment
Our brakes control our stopping function, and
must be correctly adjusted if we are to stop tape
motion without throwing loops (all tape tension
imparted by the turntables is lost (he moment we press
the stop button). So we must always have a greater
braking force acting on the turntable which is supply 
ing the tape than on the turntable reeling in the tape.
Mechanical adjustments, where we control brak 
ing forces, are provided for each turntable. In some
cases we must adjust for each direction of rotation of
the reel, in others, we will adjust only for one direc 
tion of rotation and the other direction will be auto 
matically acceptable.
Duplicating equipment at Magnetic Tape Duplicators,
Hollywood. Ampex duplicating equipment produces
copies of master tapes at high speed with as many as
ten copies produced with each run of the master.
in series with the reel motor (or clutch) and thus the
torque of the turntable. Measurement is made with
a spring-type scale and adjusted to the manufacturer ’ s
specifications.
i -L
Demagnetization is usually achieved through a
small, hand type, device that is readily available on
the open market or from tape equipment manufac 
turers. It is easily operated and very effective when
used correctly.
our bias and erase oscillator. If there is any asym 
metry from this circuit it will show up as a d-c com 
ponent — capable of permanently magnetizing our
record and erase heads and causing distortion and
noise in our recorded signal.
When we use a push-pull oscillator we can bal 
ance out any asymmetry by using a variable cathode
resistor common to each tube in the circuit. This
resistor is adjusted for a minimum noise as read
at the output of the equipment.
Cleaning
It does little good to buy professional quality
equipment if we allow accumulations of matter to
build up on the tape transport. One of the easiest, one
of the most important, and probably one of the most
neglected maintenance procedures is the cleaning
of the transport.
The major source of foreign material on the trans 
port is the magnetic tape. Oxide and lubricant from
the tape will gradually accumulate on the compo 
nents in the tape threading path, and if it is not re 
moved our equipment will not operate satisfactorily
— even though everything else on the recorder is in
perfect condition. For example, if the accumulation
is on our precisely machined capstan (or the capstan
idler) we will have excessive flutter. If it is on a tape
guiding component it is apt to cause a vibration
in the tape — similar to the vibration that occurs
when we pluck a violin string — and again, we will
have excessive Hutter. If it accumulates on the heads,
the tape will not maintain good contact, and our
recorded level and/or frequency response will suffer.
So we must clean the transport on a regularly
scheduled basis, with each component in the tape
threading path receiving attention. But we must be
Magnetic film transports are used extensively in the
motion picture industry for dubbing master sound
tracks. Here is the Ampex 35-mil film transport instal 
lation at Glen Glenn Sound Studios, Hollywood.