Movie Makers (Jan-Dec 1951)

323 "Movie Makers," exclusively, brings you an authoritative technical analysis of the new RCA "400" magnetic projector to the "record-erase" position, and to insert a plug in the input jack. If either of these last two operations is not performed, the erase head will not be energized. To reproduce sound from a standard optical track film, the track selector and the function selector controls are turned to the "Opt" and "Optical Sound" positions. When the track selector knob is moved to optical position, a microswitch completes the circuit for the exciter lamp and at the same time retracts the magnetic head to prevent it from making contact with the film. The amplifier in the new magnetic projector meets all the performance requirements of the standard projector; and in addition it has all the facilities necessary for magnetic recording, reproducing and the erasure of sound on the edge-coated film. The modification of the amplifier proper has been accomplished, first by substituting a pentode for the triode voltage amplifier. Second, a 9-pole, 4-position switch has been used to permit the selection of the desired amplifier function — magnetic sound, optical sound, magnetic record-erase, or public address. Since the output stage of the amplifier has remained essentially unchanged, the power output rating is identical to that of the original amplifier. Overall characteristics of the amplifier for optical playback and public address have also remained unchanged. The amplifier output networks are adjusted so that amplifier distortion will always be small compared to that of the recorded signal. Thus, optimum signal-to-noise ratio is obtained during recording. Under these conditions, the ratio is 50 db. with the tone-control in the flat position. The overall frequency response of the system, for a signal recorded and played back on this projector, is flat within 5 db. from 100 to 6000 cycles per second. Following are general specifications of the new RCA "400" magnetic sound projector: amplifier power output. 10 watts; film speed (24 frames per sec), 7.2 inches; frequency response (magnetic), 100-7200 cycles; signalto-noise ratio (magnetic), 50 db.; projector dimensions. 20}/2 inches long, 9 inches wide, and 12 inches high; projector weight, 45 pounds; speaker dimensions, 19% inches long, 9 inches wide, and 15% inches high; speaker weight, 26 pounds. Recording on the RCA "400" magnetic sound projector requires no special preparation or studio facilities. The new method also eliminates the time normally consumed in waiting for processing of a photographic track. The cost of producing sound on 16mm. film with this multi-use equipment has been estimated to be about one third of the cost of achieving comparable results photographically. In addition, film waste due to recording errors is eliminated. The RCA "400" magnetic sound projector thus makes available many uses of 16mm. film where allowable costs are restricted by the need for only a limited number of prints. It will be of equal significance where a varied distribution of a single basic production demands a varied sound treatment without the cost and time involved in laboratory processing. For all such users, the new projector means high quality sound, greater flexibility and greater operating convenience, with marked savings in time, film and processing costs. FIG. 2: Closeup reveals design of recorder-playback head at topcenter and track selector knob, here in "Mag" position. FIG. 3: The erase head wisely separated from the recorder unit, is here in erase position with rewind lever at play. FIG. 4: To rewind, erase head must be moved from film path before rewind lever can be actuated. Added protection from accidental erasure is designed into function selector point.