Ampex 385 Operation Maintenance

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V

AMPIEX

MODEL 385

OPERATION AND

MAINTENANCE MANUAI.

MODEL 385

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INSTRUCTION MANUAL
FOR
AMDEX MODEL 385 THREE CHANNEL MIXER

The Ampex Model 385 Three Channel Mixer has been designed to
mix three low impedance mic raphone input sources to feed the input of
the Bridging Meter Control Panel on the Ampex Model 300 Magnetic Tape
Recorder. Sufficient amplification is provided before mixing to insure
the highest possible Signal-to-noise ratio and to allow the use of unte rrnin-
ated inputs.

SPECIFICATIONS

Inputs: Three microphone level inputs incorporating high
level mixing. Shipped for 200 to 250 ohm impedance non-terminating. Can
be strapped for 50 ohm, 125 to 150 ohm. and 500 to 600 ohm.

Output: Cathode follower output (unbalanced) designed to feed
only the Bridging Input Meter Panels of the Model 300 Magnetic Tape
Recorder.

Gain: Sufficient to produce the recommended operating level on
the tape with an input signal of -94 dbm. on any channel. (Mixer level
controls and Meter Panel Level control set for zero db attenuation.)

Frequency ReSponse: t ldb30to 15.000cyclea.

Nois e: 65 db below signal for inputs of -50 dbm. This repre-
sents a noise equivalent to an input signal of -llS dbm.

Dis to rtion: With a -50 dpmtinput signal and sufficient gain
to modulate the tape 15 db above the recommended operating level. distortion
is . 2% RMS total harmonic on a 400 cycle tone.

Controls: Three 20 step attenuators (2 db per step tapered
to infinity) are used as high level mixing controls. The record level control
on the Meter Control Panel of the recorder functions as the master gain
control. An External Line Key provides for switching the tape recorder to
an external line.

Tube s: 5 6.17 Vacuum Tubes
1 6C5 Vacuum Tube

Pow: r Requirem ents: 1.8 ampere: at (6.3 volts, ac. and
10 milliamperes at 390 volts, dc, obtained from Electronic Assembly of
the Model 300 Magnetic Tape Recorder.

MODEL 385 - Page 1
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