Ampex 351 - Page 37

equipment, disregarding the human
r
8
Magnetic equipment in the recording industry. Ampex
Model 300-3 installed at United Recording Studios,
Hollywood.
ation when tape is exhausted from the reel, or if the
tape breaks.
J
Electronic Circuits
There arc three main electronic circuits which
usually are provided — a record amplifier, a bias
and erase oscillator, and a reproduce preamplifier.
These will normally be quite conventional audio
Operational Requirements
We must provide adequate torque for the fast
forward and rewind modes, with the actual torque
requirements varying with the tape width. But we
must bear in mind that excessive torque might result
in our exceeding the elastic limits of the magnetic
tape, and result in breaking or deforming the tape.
The tape must be stopped without damage. The
elastic limit of the tape again determines our maxi 
mum braking force. Since a minimum brake differ 
ential must be maintained, this factor also determines
our lower braking limit
We must also have reasonable start and stop
times.
— The amount of wrap-around the
be held to a minimum, because the
build-up of tape tension will increase with the degree
of head wrap. Depending on the flexibility of the tape
and the geometry of the head, it is possible that a
large tape wrap will result in the tape bowing out at
the apex of the head and losing contact at the gap. A
wrap of 4 to 6 degrees on each side of the head gap
has proved quite satisfactory.
Large tape wraps (in degrees) around small diam 
eters should be avoided. This is not only a case of
holding tension build-up to a minimum. While there
are no qualitative data available it has been proved
that sharp bends around small diameters result in
measurable losses of recorded high frequencies during
the first three or four playbacks.
Tape wrap around the reel idler must be sufficient
to ensure a good, solid coupling between the tape and
the idler. On A mpex machines operating at 60 and
120 ips, it has been necessary to groove the tape con 
tacting area of the idler pulley so that the air film is
dispelled and good coupling is ensured. The effect of
insufficient coupling can be seen in the fast forward
or rewind modes of a standard recorder; the air film
picked up by the fast moving tape acts as a cushion
and the idler barely turns. The air film can be advan 
tageous if we wish to operate in a fast winding mode
without mechanically lifting the tape from the heads,
but it proves quite troublesome at times (especially
when we are trying to get a good pack during a fast
winding mode using 1-inch tape).
DRIVE LAYOUT — The heads, capstan and capstan
idler should be arranged so that the tape from the
heads first contacts the capstan not the idler. In those
layouts where the tape from the playback head con 
tacts the idler before reaching the capstan, there will
be flutter — caused by idler run-out, by variations in
the hardness of the rubber around the periphery, and
by bumps or voids in the tire.
NUMBER OF COMPONENTS — The number of tape
contacting components should be be held to a mini 
mum, because every additional part means more
build-up in tape tension. This build-up is a function
of the number of tape contacting components, the
degree of tape wrap around each, and their surface
roughness. The geometry of the layout must eliminate
unnecessary guide posts, idlers, etc. Tension build 
up can also be reduced by mounting the necessary
components on ball bearings, or on other types of low
torque bearings.
threading, with reels compatible with those now
existing, offers a definite improvement. The threading
path can then be engineered for optimum perform 
ance of the
equation.
TAPE WRAP
heads should
Therefore, we must provide optimum torque and
braking force, adequate for fast winding and accept 
able start and stop times, but which will not exceed
the elastic strength of our medium. Typical values
for a ’ /a-inch tape equipment would be 35-40 ounce 
inches of torque, with a maximum braking force of
approximately 30 ounces, measured on a 2 J Zi-inch
radius (N.A.B. reel hub).
TAPE THREADING — From the human engineering
standpoint, tape threading paths using the wrap 
around principle are superior to those utilizing a
"drop-through the-slot ” type. The utmost efficiency in
threading tape would be provided by a transport that
had a simple wrap-around path from supply reel to
takeup reel, with no necessity for threading behind
idlers, guides, etc. Unfortunately this perfection is
impossible of achievement — although it can be
approached — because of the necessity for threading
the tape between the capstan and the capstan idler.
Of course, a transport employing a system of self-