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AT-MX341a SmartMixer
®
Four-channel Automatic Microphone Mixer
Installation and Operation
Page 2
Contents
Introduction .......................................................................................................................3
What is the SmartMixer®? ........................................................................................................3
Features .....................................................................................................................................3
Front Panel ................................................................................................................................4
Rear Panel .................................................................................................................................5
Installation and Setup ................................................................................................6
Priority Microphones and Lockout Bus .................................................................................6
Preamplifier Gain .....................................................................................................................7
Output Gain ..............................................................................................................................7
Phantom Power ........................................................................................................................7
Output Level LED Meter ..........................................................................................................8
Adjusting “Off” Attenuation ...................................................................................................8
Control Voltage Out .................................................................................................................9
Daisy-chaining Mixers ...........................................................................................................10
Rack Mounting ........................................................................................................................10
Security Caps ..........................................................................................................................10
Specifications .................................................................................................................11
Warranty .............................................................................................................................12
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Introduction
Please Note!
This manual assumes use of microphone-level inputs and line-level output, the most typical
SmartMixer application. However, all inputs and the output may be individually switched
internally to achieve any combination of mic- and line-level input/output. See page 7 for details.
What is the SmartMixer?
The AT-MX341a SmartMixer®Automatic Microphone Mixer is a microprocessor controlled,
automatic switching, four-channel microphone mixer.
The microphone inputs are XLRF-type balanced, with 12-volt phantom power available on
pins 2 and 3. The output is XLRM-type balanced, non-inverting.
AT-MX341a mixers can be daisy-chained via the included AT8325/1.0 Link Cable and special
connectors on the rear panel. The control bus and the audio are carried between mixers by the
link cable. The result is that all microphones on a multi-mixer system can be controlled by one
microphone connected to any mixer. Since all of the mixers are independently powered, there
is no practical limit to the number of SmartMixers that can be daisy-chained.
Features
To custom-tailor conferencing needs, the mode of each microphone channel can be independently switched via the front panel “priority pre-select” DIP switches. The combination of
switch settings results in three different modes of priority selection/operation.
In any of the three modes of automatic operation, when everyone stops talking, the last
microphone “on” will remain “on.” In a teleconferencing, recording, or broadcast application,
this feature will provide continuous room ambience. This feature is cascaded throughout all
linked mixers so that only one microphone in the entire system will remain on.
Each input channel has an independent gain control on the front panel. Substantial gain
reserve and adjustment range permits microphones of widely differing sensitivities to be used
together successfully.
When a microphone is “off,” its input is only attenuated. This attenuation is factory set at
8 dB. The amount of “off” attenuation can be internally adjusted between 6 dB and 20 dB if
desired. (See page 8, “Adjusting ‘Off ’ Attenuation.”)
A “manual” setting on the front panel bypasses the AT-MX341a’s automatic switching and
attenuation functions, causing the unit to behave like a conventional 4-channel mixer. In this
mode, the relative level of each microphone is strictly a function of the position of its respective
front-panel gain control.
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AT-MX341a Front Panel
1. Power switch.
2. Power “on” indicator.
3. Input Gain controls. Adjust inputs for microphone sensitivities and/or
operating conditions.
4. Selected Channel LED indicators. Indicate which channels are “on” or “active.”
5. Output Level LED meter. Indicates RMS output level of the mixer. “Zero” (0) level is
factory calibrated for an output of +4 dBm into 600 ohms (Master Level control fully
clockwise). Can be set for peak output level indication via internal switch (see page 8).
6. Priority Pre-select switches. A switch in the “up” position assigns the respective
channel priority over the other channels. A priority channel can not be locked out by
other channels. Any combination of priority/non-priority selections is allowed.
7. Master Level control. Normal setting is fully clockwise (full output). If reducing the
mixer’s output is necessary, carefully turn the control counter-clockwise as needed with
a small screwdriver. Once set as desired, the control may be protected from unauthorized
adjustment by covering the panel hole with a sticker provided with the security caps.
(This control does not affect the meter indication.)
8. Master Threshold/Manual control. Sets the reference level that must be exceeded
for a microphone to be considered “in use.” Adjust to keep background noise level from
triggering microphones. “Manual” setting bypasses all of the SmartMixer’s automatic
functions.
9. Lockout LED indicator. Shows when lockout bus is active. Also aids in setting
Master Threshold.
Figure 1. Front panel
Gain 4Gain 3Gain 2Gain 1
Power
AUTOMATIC MICROPHONE MIXER
Selected Channel
AT-MX341a
Master
Threshold
Manual
Master
Level
Lockout
Output Level
-20 -10 -6 -3 0 +3 +6
Priority Pre-select
1
2
3
4
➋
➌
➏➍
➊
➐ ➒
➎
➑
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AT-MX341a Rear Panel
1. Power input. Requires 12 volts AC or 15 volts DC, either polarity; 150 mA minimum.
2. Link In/Out. Provides for daisy-chaining of multiple mixers when more than four
microphones are used.
3. Control Voltage Out. Provides 0 to +4 VDC (active high) to trigger external devices such
as speaker switching, camera switching and indicator lights.
4. Output. Balanced line-level output. Can be changed to mic-level output via internal
switch (see page 7). XLRM-type connector.
5. Inputs. Balanced microphone inputs for low impedance dynamic or condenser mics.
Can be changed to line-level inputs via internal switches (see page 7). XLRF-type connectors.
Figure 2. Rear panel
5
Input 2Input 3Input 4Output Input 1
Link In
Control Voltage Out
Link Out
AC 12V Input
1234
GND
➋➊
➎➌ ➍
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Installation and Setup
AT-MX341a SmartMixer setup tips:
1. Turn Master Threshold control to minimum threshold, immediately clockwise of the
“Manual” setting.
2. Set all Priority DIP switches to “down” position.
3. Turn all four microphone Gain controls fully counter-clockwise.
4. Connect the AC adapter to the mixer and plug in to outlet.
5. Turn Power switch “on.” The mixer will perform a self-test and turn each microphone
“on” and “off ” consecutively.
6. Connect a microphone to Input 1 and turn the Gain 1 control to the “nine o’clock”
position. The channel 1 LED will light if the microphone is operational.
7. Adjust the Gain 1 control for proper meter indication when speaking into microphone
(peaks at 0).
8. Gradually increase the Master Threshold control until the Lockout LED flashes when
speaking at a normal level.
9. Plug in up to three other microphones and adjust each respective Gain control for proper
meter indication. It should not be necessary to readjust the threshold level.
10. Priority can be assigned to one or more microphones by moving the appropriate DIP
switch(es) to the “up” position. Any microphone(s) assigned in this manner cannot be
locked out by any other microphone.
11. “Manual” mode can be selected at any time by simply turning the Master Threshold
control fully counterclockwise. In this mode, the unit will behave like a conventional
four-channel microphone mixer (all automatic functions are bypassed).
12. The Master Level recessed control on the front panel may be adjusted with a small
screwdriver if necessary. This control is at the last stage in the mixer, and does not affect
microphone gain, threshold setting, or meter indication.
Priority Microphones and the Lockout Bus
Once the Master Threshold control has been properly adjusted, an audio signal appearing in
any channel causes the lockout control bus to activate and the Lockout LED indicator to light.
The Priority Pre-select switches then determine whether or not a particular mic is affected by
lockouts caused by other mics: a channel Priority switch in the “down” position will allow
lockout* of its mic; the same switch “up” will not allow lockout of its mic.
* Note that any mic which is described as “locked out” or “off ” is really just being attenuated
by between 6 dB and 20 dB from the level otherwise determined by its Gain control setting,
sensitivity and placement. See the “Daisy-chaining Mixers” section on page 10 for further details.
There are basically three “modes” of automatic operation:
Mode 1... All Priority Pre-select switches Up
The Lockout indicator will come on with any audio input, but no mic will be locked
out…because none are connected to the lockout bus. (This mode is often called
“Free-for-all”…or sometimes “City Council”!)
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Mode 2…All Priority Pre-select switches Down
In this mode, only one mic at a time can be “on.” The lockout bus shuts down all other mics
until the first speaker pauses. As soon as the controlling microphone goes silent, the lockout
bus goes inactive and any other mic can come on. This switching takes place without any
syllable-grabbing delay, or pops or clicks. (This mode is known as “First-come-first-served”
or “Filibuster.”)
This mode is very useful when the gain setting of the overall sound system must be close to
the threshold of feedback, and additional microphones coming on could throw the system into
feedback. The SmartMixer will not allow multiple microphones to be on at the same time in this
mode. The switching is so fast and silent that the meeting can still be completely interactive.
Mode 3…One Priority Pre-select switch Up
The selected priority microphone can come on at any time and can override any other mic that
is on (popularly called “The Chairperson” mode).
(Note that there may be special circumstances where two or three mics could be set to priority,
so those speakers could talk whenever desired, but still override one or two non-priority mics.)
If multiple SmartMixers are used with AT8325/1.0 Link Cables, Priority Pre-select switches
on all channels in use will have the control effects described above.
Preamplifier Gain
The SmartMixer has a substantial gain range, allowing it to accept a wide variety of microphones. However, if in some instances higher-output microphones are used for close talking,
it may be necessary to reduce the preamplifier gain. This can be done by changing switch
settings inside the unit. With the unit unplugged, remove the two screws on each side of the
unit and remove the top cover. Locate the internal switches designated on the circuit board
by “SW9,” “SW10,” “SW11” and “SW12” (Figs. 3 and 4, page 8). Changing the settings of these
internal switches will cause a gain reduction of 10 dB for channels 1, 2, 3 and 4 respectively.
The preamplifier gain may be reduced further, allowing the SmartMixer to accept line-level
sources. Changing the settings of the internal switches designated by “SW1,” “SW2,” “SW3”
and “SW4” will cause an input reduction of 50 dB for channels 1, 2, 3 and 4 respectively. Note
that the appropriate internal switches can be used in combination for a total sensitivity
reduction of up to 60 dB for each channel.
Output Gain
The SmartMixer’s output is factory set at line level. Should mic-level output be desired,
simply unplug the unit, remove the top cover and locate the switch on the circuit board
marked “SW15” (Figs. 3 and 4, page 8). Changing the setting of this switch will cause a
50 dB reduction in output.
Phantom Power
Each of the SmartMixer’s inputs supplies +12V DC phantom power. Should it be required
to disable the phantom power, simply unplug the unit, remove the top cover and locate the
switches designated on the circuit board by “SW5,” “SW6,” “SW7” and “SW8” (Figs. 3 and 4,
page 8). Changing the settings of these switches will disable phantom power on channels 1, 2,
3 and 4, respectively. Note that, although they do not require phantom power for operation,
most balanced-output dynamic microphones can be used without disabling the SmartMixer’s
phantom power.
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Adjusting ”Off” Attenuation
In instances when the number of microphones in use is high, it may be necessary to increase
the amount of “off ” attenuation per microphone to keep the total ambient noise level low.
There are “off ” attenuation adjustments inside the unit. To adjust the “off ” attenuation of
channel 1, unplug the unit, remove the top cover and locate the trimpot designated on the
circuit board by “VR5” (Figs. 3 and 4). It is factory set at approximately 8 dB, the attenuation
at the middle of the control’s rotation. When the control is turned fully counter-clockwise,
“off ” attenuation is approximately 20 dB. Conversely, when the adjustment is turned fully
clockwise, “off ” attenuation is approximately 6 dB. VR6, VR7 and VR8 control “off ” attenuation
for channels 2, 3 and 4 respectively.
Figure 3. Internal view of mixer.
Figure 4. Detail of internal controls.
Front Panel
Rear Panel
Output Level LED Meter
The Output Level LED meter is factory set
to indicate RMS output. Should peak output
indication be desired, simply unplug the unit,
remove the top cover and change the setting
of the switch designated on the circuit board
by “SW16” (Figs. 3 and 4). “Zero” (0) level is
factory-calibrated at +4 dBm into 600 ohms.
8
Mic
Line
Phantom
Off
Mic
Line
Phantom
Off
Mic
Line
Phantom
Off
SW7
Mic
Line
Phantom
Off
SW4 SW8
Line
Mic
Output
–10 dB 0 dB–10 dB 0 dB–10 dB 0 dB–10 dB 0 dB
SW16
Peak RMS
SW3SW6SW6SW2SW5SW1
SW9
SW10 SW11 SW12
VR5
VR6 VR7 VR8
SW15
MeterPadPadPadPad
–20 dB –6 dB –20 dB –6 dB –20 dB –6 dB –20 dB –6 dB
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CV
G
R
Driving One LED
I
≈
2v
R+40Ω
Driving Lamps
2N3904
+
CV
10
KΩ
G
G
CV
Driving Logic Gates
Equivalent Output
Circuit for Control
Voltage Out
CONTROL
VOLTAGE
40Ω
GND
Relay Driver
2N3904
IN4001
+
CV
10KΩ
RELAY
COIL
G
Control Voltage Out
When a microphone channel turns “on,” as indicated by a Selected Channel LED on the front
panel, the channel’s associated Control Voltage Out goes “high” (+4 VDC). This signal can be
used to light indicator lamps, switch speaker zones on and off, select video cameras, etc. The
control voltage should not be connected directly to an inductive load such as a relay coil, as
damage to the mixer may result. Several interface circuit possibilities are shown in Figure 5.
Figure 5. Control interface examples.
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Daisy-chaining Mixers
When more than four microphones are needed, it is possible to daisy-chain multiple
SmartMixers together through the Link In/Out connectors on the backs of the units (Fig. 2).
Connect Mixer #1 Link Out jack to Mixer #2 Link In jack, etc. Mixer #1 output contains only
audio from the first four microphones; Mixer #2 output then contains audio from all the
microphones plugged into Mixer #1 and the microphones plugged into Mixer #2. The last
mixer in the chain contains audio from all preceding mixers. The combined output is then
taken from the last mixer in the chain. Because lockout information is passed between mixers
through Link In/Out, the last-microphone-on condition is not violated. Thus only one
microphone per installation will stay on when no one is speaking.
Note that one or more mixers can be switched to “Manual” mode without affecting the
automatic operation of any other mixers in the chain.
Rack Mounting
Provided with each mixer are two rack ears, one long and one short, and six self-tapping
screws to attach the ears to the unit. When using more than one SmartMixer in a system, it
may be advantageous to mount two mixers in a 1U rack space. This can be accomplished using
the two short rack ears and an optional joining plate (Model AT8628), which allows two units
to be connected side-by-side in a single rack space.
Security Caps
For permanent installations where microphone selections, positions and acoustic conditions
are constant, it may be advantageous to remove the front panel knobs and install security
caps to prevent unauthorized adjustments. To install, simply press the caps into place,
covering the Gain and Threshold controls. Place the provided sticker over the Master Level
access opening in the panel. The system should be tested carefully before installing the security
caps because they are intended to be “permanent” and are very difficult to remove.
If removal of installed security caps becomes necessary, first remove the two screws on each
side of the unit and remove the top cover. Then remove the six screws that attach the front
panel: four on top and two underneath. Remove the front panel. With the panel removed, the
two locking tabs on each security cap can be accessed. The cap can be released by carefully
squeezing the two tabs together.
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Specifications
†
Input Impedance
Mic
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 4,000 ohms
Line
. . . . . . . . . . . . . . . . . . . . . . . . . . . 30,000 ohms
Output Impedance
Line
. . . . . . . . . . . . . . . . . . . . . . . . . . . 200 ohms
Mic
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 320 ohms
Maximum Input Level
Mic
. . . . . . . . . . . . . . . . . . . . . . . . . . . . –20 dBV
Line
. . . . . . . . . . . . . . . . . . . . . . . . . . . 30 dBV
Maximum Output Level*
Line
. . . . . . . . . . . . . . . . . . . . . . . . . . . +14 dBm (600 ohms)
Mic
. . . . . . . . . . . . . . . . . . . . . . . . . . . . –40 dBm (600 ohms)
Nominal Output Level (0 VU)*
Line
. . . . . . . . . . . . . . . . . . . . . . . . . . . +4 dBm (600 ohms), +4.4 dBV (open circuit)
Mic
. . . . . . . . . . . . . . . . . . . . . . . . . . . . –46 dBm (600 ohms), –44 dBV (open circuit)
Maximum Gain
. . . . . . . . . . . . . . . . . . . . ≥70 dB
Frequency Response
. . . . . . . . . . . . . . . 60 Hz to 30 kHz at –3 dB points
Dynamic Range
1
. . . . . . . . . . . . . . . . . . . 75 dB ±10 dB, dependent upon gain control settings
Equivalent Input Noise
. . . . . . . . . . . . –120 dBV (150 ohms) at maximum gain
Input Attenuation
. . . . . . . . . . . . . . . . . 10 dB
Mic/Line Input Pads
. . . . . . . . . . . . . . . 50 dB
Microphone Phantom Power
. . . . . . . +12V DC
Control Voltage Out
. . . . . . . . . . . . . . . +4V DC
Power Supply
. . . . . . . . . . . . . . . . . . . . . . 12V AC, 150 mA, min.
Operating Temperature
. . . . . . . . . . . 32° to 104° (0° to 40° C)
Dimensions
. . . . . . . . . . . . . . . . . . . . . . . . 8.25" (210 mm) W x 9.38" (327 mm) D x 1.75"
(44 mm) H (including feet, knobs and connectors)
Weight
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 lbs. 7 oz (1.6 kg)
Included Accessories
. . . . . . . . . . . . . . . AC power supply, AT8325/1.0 Link Cable
Optional Accessory
. . . . . . . . . . . . . . . . AT8628 Double Rackmount Joining Plate
†
In the interest of standards development, A.T.U.S. offers full details on its test
methods to other industry professionals on request.
* Master Level control at maximum (fully clockwise).
1
Input terminated with 150 ohms, A-weighted using Audio Precision System One.
Summary of Internal Controls
Function Ch 1 Ch 2 Ch 3 Ch 4 Output
50 dB Mic/Line Atten. SW1 SW2 SW3 SW4 SW15
12V Phantom Power SW5 SW6 SW7 SW8 -10 dB Input Atten. SW9 SW10 SW11 SW12 -“Off” Attenuation VR5 VR6 VR7 VR8 -Meter RMS/Peak -- -- -- -- SW16
See diagram on page 8 for locations/positions.
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One-Year Limited Warranty
Audio-Technica brand products purchased in the U.S.A. are warranted for one year from date of purchase by Audio-Technica U.S., Inc.
(A.T.U.S.) to be free of defects in materials and workmanship. In event of such defect, product will be repaired promptly without charge or, at
our option, replaced with a new product of equal or superior value if delivered to A.T.U.S. or an authorized service center prepaid, together
with the sales slip or other proof of purchase date.
Prior approval from A.T.U.S. is required for return.
This warranty excludes defects due
to normal wear, abuse, shipping damage, or failure to use product in accordance with instructions. This warranty is void in the event of
unauthorized repair or modification.
For return approval and shipping information,
contact the Service Department, Audio-Technica U.S., Inc., 1221 Commerce Drive, Stow,
Ohio 44224.
Except to the extent precluded by applicable state law,
A.T.U.S. will have no liability for any consequential, incidental, or special
damages; any warranty of merchantability or fitness for particular purpose expires when this warranty expires.
This warranty gives you specific legal rights, and you may have other rights which vary from state to state.
Outside the U.S.A., please contact your local dealer for warranty details.
Audio-Technica U.S., Inc., 1221 Commerce Drive, Stow, Ohio 44224 330/686-2600
P50791-B/ W ©1995 Audio-Technica U.S., Inc. Printed In U.S.A.
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