Input Channels; Mic/Line Level Selection; Gain / Trim; Faders - Sound Devices 302 User Manual

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30. Mix In
An input to the master bus designed exclusively
to link the Tape Out/ Mix Out of 302, 442, MixPre,
or MP-2 to the 302 for additional inputs. Pin-1 =
ground, pin-2 = left, pin-3 = right. Shell of TA3 con-
nector must be grounded to pin-1 to open connec-
tion.
31. Battery Tube
Holds three-AA batteries for internal powering.
I C
NPUT HANNELS
The inputs of the 302 consist of three, full-featured
microphone preamplifi ers. Each channel has a wide gain
range to accommodate nearly all signal types. The 302
easily accepts signals from low-sensitivity ribbon and
dynamic microphones, medium level wireless and con-
denser mic outputs, and "hot" line-level signals.
302 input channels are transformer-balanced. The isola-
tion characteristics of transformers are superior to other
balancing techniques for the hostile and uncontrolled
environments of fi eld production. Transformers pro-
vide galvanic isolation from the driving source, mean-
ing there is no direct electrical connection. Signals are
"transformed" magnetically. The input transformers in
the 302 use premium magnetic core material to achieve
high signal handling capability (especially at low
frequencies) while keeping distortion to a minimum.
Because of their inherently high common mode imped-
ance, transformers are unrivaled by any other type of
input for common-mode noise rejection.
The inputs of the 302 can be used balanced or unbal-
anced. When unbalancing, ground pin-3 to pin-1 of
the XLR connector. There is no change in gain between
unbalanced and balanced connections into the 302.

Mic/Line Level Selection

The Mic/Line switch on the input panel is used to select
the input level for each channel. Taking into account all
gain stages, the 302 has up to 75 dB of available gain
from mic input to line output. When in the LINE posi-
tion, the input channel sensitivity is reduced by 40 dB.

Gain / Trim

Like traditional mixing consoles, the 302's microphone
preamp gains are set via the gain control. The gain, or
trim, adjusts the input sensitivity of a channel input so
that the channel fader can be set to operate in a usable
range. Once set, the gain is typically kept at the set level
and all mixing is done on the channel fader. The gain
adjustment features a pop-up knob so that it can be ad-
justed easily and then hidden from the mixing surface.
Accepts alkaline and lithium cells or NiHM recharge-
able cells.
32. DC Input
Accepts DC voltages from 5 - 18 V for mixer power-
ing. Four-pin Hirose connector wired pin-4 positive
(+), pin-1 negative (-). Ext DC is completely isolated
(fl oating) from the rest of the circuitry.

Faders

While both the gain and the fader control the gain of
a given channel, the fader is the primary channel level
control used in operation. The gain can be thought of
as a "coarse" gain adjustment to be adjusted during
setup, and the Fader is a "fi ne" level adjustment to
be adjusted while recording. With a properly set gain
control, the fader can be set to a nominal 0 (unity) level.
With the fader at unity, the dynamic range of the mixer
is maximized. There is a wide range of control for the
input, allowing for smooth level changes with adequate
control of attenuation and gain.

Microphone Powering

Phantom powering and T-powering are methods of
providing power to microphones by applying a voltage
using the same wires that carry the audio signal. The
302 produces phantom or T-power for microphones
requiring power.
Condenser microphones require power for various parts
of their operation, including impedance converters,
preamplifi er circuitry, and in some cases, to polarize mi-
crophone capsules. The 302 can provide either phantom
power or T-power to each channel and is selected per
channel.
If neither phantom or T-power are required, for in-
stance with dynamic microphones, it is good practice to
turn off microphone powering.

Phantom Power Basics

Phantom powering is a fi xed DC voltage between 12
and 48 volts. This voltage is resistively applied to pin-2
and pin-3 of an XLR connector relative to pin-1. (Note
that as there is no voltage difference between the sig-
nal pins -2 and -3—a dynamic mic can operate just fi ne
in the presence of phantom powering.)
When phantom is selected, the 302 can provide up to 10
mA to each input at 48 V, suffi cient for the most power-
hungry condenser microphones. When acceptable,
using 12 V phantom is recommended to extend battery
302 Compact Production Mixer
User Guide and Technical Information