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278 IX. SOUND-RECORDING EQUIPMENT AND ARRANGEMENT
1. Signal-to-noise ratio.
2. Absence of distortion.
3. Frequency range (with and without filters).
4. Tonal fidelity.
5. Tonal balance.
Fig. 64. RCA film recording amplifier MI-10238 (type PA-142) main recording amplifier.
The MI-10238 main recording amplifier incorporates the facilities of a main-gain voltage amplifier, an electronic mixer, high and low-pass filters, a dialog and filmloss equalizer, a ground-noise-reduction amplifier, and a recording power amplifier in a single unit. A telephone jack and associated press-to-talk switch is provided for use of a sound-powered phone. A jack is provided for monitoring with a high-impedance crystal headset. Normally associated equipment (PM-51) : MI-10221-C mixer amplifier "A" and "B" DC power supplies PR-32 or PR-33 recorder. Overall characteristics : Input impedance, 500 or 250 ohms; PA output impedance, 500 ohms; Source impedance, 500 or 250 ohms; PA load impedance, 500 ohms; Overall gain (input and galvo gain controls max., GNR gain min.), 69 db ± 1 db (may be increased 6 db — see compressor section gain) ; Overall frequency characteristics, in accordance with current Hollywood recording techniques (+0, 1 db overall from 60 to 10,000 cycles without filters) ; Power supply requirements: 250 volts dc at 160 ma (MI10501-A regulated power supply or equivalent regulated power supply of low internal impedance is essential). 6.4 volts dc at 5.8 amperes. Physical characteristics : Length, 26% inches; Width, 19% inches; Height, lO1^ inches; Weight, 88 pounds (approx.) ; Finish, light-umber-gray wrinkle case, reverse-etched nickel-silver control panel. Metering : Internal metering is provided for "A" and ' ' B " voltage and GNR current. Voltage amplifier and compressor section: The compressor offers either linear operation or two electronic positions. The " De-ess off" position offers a flat frequency characteristic and the ''De-ess on" position provides a response in the control circuit which corrects for sibilants (elimination of spectral energy distortion) to provide more natural response for dialogue recording.