Operating Instruction Manual
TOA ELECTRIC CO., LTD.
KOBE, JAPAN
Model RX-31C
TOA MIXING CONSOLE
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General Description......................................2
Features......................................................2
Front Panel..................................................3
Rear Panel...................................................4
Rack Mounting Instructions............................5
Input Connections.........................................6
Connection Examples.....................................7
Block & Level Diagrams.................................8
Avoiding Ground Loops..................................9
Effective Mixing..........................................10
Specifications..............................................11
Characteristic Diagrams.................................12
Appearance..................................................12
1. XLR (Cannon) Connector
XLR Connectors are wired to NAB standards. Pin 1 is ground (shield), Pin 2
is cold (low, minus), Pin 3 is hot (high, plus).
2. Descriptions of components and functions
Various mixing console descriptions are used, depending on individual
manufacturer's standards. In our Operating and Instruction Manual, explana-
tion of components and functions is made according to our usage for them.
3. Phantom Power Supply
The RX-31C incorporates a 48V DC Phantom Power circuit. If phantom power
is required, the Phantom ON/OFF switch on each input channel for which
phantom power is required should be "on". When using phantom power, avoid
connecting unbalanced microphones or connecting other circuits in which the
center tap of the unit's input transformer is grounded.
–1 –
Contents
Precautions
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The RX-31C is an eight input, one program output and one line output mixer,
designed especially for sound reinforcement systems in auditoriums, churches
and similar applications. Each input channel is transformer isolated and accepts
either a low impedance microphone or a high level source. A MIC/LINE selector
switch on each input channel permits selection of the type of source. A phantom
ON/OFF switch on each input channel applies 48V DC phantom power for con-
denser microphones. An input TRIM control on each input channel provides 30dB
of gain adjustment prior to the main channel fader. A channel ON/OFF slide
switch on each input channel connects or disconnects the input signal to the mix-
ing bus. The adjacent green LED illuminates when the channel is "on". An LED
bar graph peak meter with 12 sections calibrated in 3dB steps responds instant-
ly to the program output level. Also featured is a 5 band (peaking) equalizer with
rotary controls plus switchable high pass/low pass filters for reducing wind and
scratch noise. A headphone output enables the operator to audition each input
channel, AUX input, program output or line output, depending on the position of
the phones selector switch. With an optional bracket, the RX-31C is usable in a
rack-mounted configuration.
1. Phantom power switches, each channel
2. MIC/LINE selector switches, each channel
3. Individual input level Trim controls, each channel
4. Channel ON/OFF switches
5. Peak indicator, each channel
6. LED peak meter with 12 sections calibrated in 3dB steps
7. High pass and Low pass filters
8. Five band (peaking type) equalizer (rotary type)
9. Headphone jack
10. AUX IN and REC (recording) OUT jacks
11. Rack-mountable with an optional bracket, occupies 7 spaces
–2 –
General Description
Features
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Phantom Power (48V DC) Switches-
The individual channels' switches should
be "on" when one or mo re condenser
microphones are connected, and the
switch should be "off" when dynamic
microphones are used.
MIC/ LINE Input Selector Switch (INPUT)
Selection is made in accordance with the
incoming signal. When dynamic micro-
phones are connected, the selector switch
must be set to the MIC position. When a
high level source is attached, it must be
set to the LINE position. The LINE position
is designed to automatically disconnect
the phantom powering circuit even if the
phantom power switch is "on".
Input Trim Control (TRIM)
Controls the gain of the head-amplifier
stage of each input channel, providing an
additional 30dB trim from the sensi-
tivity chosen at the input level selector
(MIC/LINE switch).
Security Cover Stud Screw
The stud screws are provided to mount
the smoked plastic security cover, which
prevents inadvertent control changes
after all controls (except the input and
master faders) are properly set.
LED Peak Meter
The LED peak meter with 12 sections
calibrated in 3dB steps, responds instan-
taneously to the pr ogram output level.
Green LED's indicate the level below the
+4dBm nominal level, and red LED's
indicate the level above the +4dBm
nominal level.
Power Switch
Pushbutton alternately switches AC
power "on" and "off".
High Pass Filter
The switchable high pass filter provides
flat response when OFF, but can be set to
cut the mixer's frequency response below
50Hz at a 6dB/octave rate.
Low Pass Filter
The switchable low pass filter provides
flat response when OFF, but can be set to
cut the mixer's frequency response above
15kHz at a 6dB/octave rate.
Equalizer IN/OUT Switch
The equalizer IN/OUT switch puts the
mixed signal either in or out of the
equalizer. The OUT position provides flat
response.
LED AC Power Indicator
The green LED illuminates when the
power switch is "on".
Headphone Jack
Headphones (mono or stereo) with mini-
mum 8-ohm load impedance may be
plugged into this jack for mono audition.
Input Channel ON /OFF Switch-
(CHANNEL)
The slide switches provide quick connects
or disconnects of individual channel input
signals to the mixing bus.
LED
Indicator-
The green LED illuminates when the input
channel switch is "on".
LED Peak Indicator (PEAK)-
The peak indicator illuminates if clipping
occures in the head-amplifier stage of the
corresponding input channel. When the
light comes on, adjustment should be
made with the input TRIM control.
Equalizer
The equalizer consists of 5 bands of
peaking equalization (rotary type), and
provides l0dB of boost and l0dB of
attenuation at 63Hz, 250Hz, IkHz, 2kHz
and 8kHz, based on ISO standards.
Phones Volume Control
Controls headphone volume.
Writing Block-
The identification of the input equipment
or microphone location can be written on
the block with an erasable felt pen or a
wax pencil.
Input Fader-
The fader continuously varies the channel
level to the mixing bus. Nominal level is
the "0" position. The fader is calibrated
in dB and assures very smooth operation.
Master Program Fader
Controls the overall signal level of the pro-
gram mix fed to the program output.
Line Output Fader
Controls the overall signal level of the mix
fed to the line output.
Phones Selector
The phones selector is a 12-position
(including "off") rotary switch used to
choose the signal which is fed to the head-
phone jack. A signal is selected from
among the program output, line output,
AUX input, and each input channel (1 to 8
input channels).
–3 –
Front Panel
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Program Output Connector (PGM OUT).
The Program Output Connector is bal-
anced and transformer isolated. The
nominal signal level and impedance are
+4dB and 600 ohms, respectively.
Line Output Connector (LINE OUT)
The Line Output Connector is balanced
and transformer isolated. The nominal
signal level and impedance are +4dB and
600 ohms, respectively. The output signal
is derived prior to the equalizer section.
Input Channel Connector(s) (INPUT)
The XLR connectors are balanced,
transformer isolated, and accept either
low or high impedance sources, depend-
ing on the position of the MIC/LINE
selector switch on the front panel, the
nominal signal level and impedance in the
MIC position are -64dBm and 1.5k ohms,
respectively. In the LINE position, the
nominal signal level and impedance are
-24dBm and l1k ohms, respectively.
AC Power Cord
Cord Hanger
-AUX Input Jack (AUX IN)
This jack is unbalanced and accepts low
or high impedance sources at nominal
-20dB level. The AUX input will accept
feeds from a tape player, wireless tuner
or other high level devices.
AC Fuse (1A)
The fuse should be replaced only with
one of identical value and type.
Recording Output Jack (REC OUT)
This is a high level, high impedance
(nominal 10k ohms) unbalanced output
jack (nominal level -l0dB). This signal is
pre equalizer and suitable for feeding a
tape recorder or other high level devices,
devices.
–4 –
Rear Panel
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