Audio-Technica AT-MX351A User manual

AT-MX351 SmartMixer

Automatic Mixer

Installation and Operation



Contents

Introduction .......................................................................................................................5

What is a SmartMixer? ...........................................................................................................5

Features .....................................................................................................................................5

Front Panel ................................................................................................................................6

Rear Panel .................................................................................................................................7

Installation and Setup ................................................................................................8

Priority Microphones and Lockout Bus .................................................................................8

NOMA ........................................................................................................................................9

Auxiliary Input ..........................................................................................................................9

Preamplifier Gain ..................................................................................................................... 9

Output Level ...........................................................................................................................10

Phantom Power ......................................................................................................................10

Output Level LED Meter ........................................................................................................10

Adjusting “Off” Attenuation .................................................................................................12

Preamp Outputs .....................................................................................................................12

Input Limiters ..........................................................................................................................12

Force-on/Force-off ..................................................................................................................12

Control Voltage Out ...............................................................................................................13

Daisy-chaining Mixers ...........................................................................................................14

Rack Mounting ........................................................................................................................14

Security Caps ..........................................................................................................................14

Specifications .................................................................................................................15

Warranty ..............................................................................................................Back cover

Compliance with FCC rules (USA only)

This device complies with Part 15 of the FCC rules. Operation is subject to the following two conditions: (1) this
device may not cause harmful interference, and (2) this device must accept any interference received, including
interference that may cause undesired operation.

Caution for FCC

You are cautioned that any changes or modifications not expressly approved in this manual could void your authority
to operate this equipment.

Note: This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant to
part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference
when the equipment is operated in a commercial environment. This equipment generates, uses, and can radiate
radio frequency energy and, if not installed and used in accordance with the instruction manual, may cause harm­ful interference to radio communications. Operation of this equipment in a residential area is likely to cause harmful
interference in which case the user will be required to correct the interference at his own expense.

IC statement (Canada only)

This Class A digital apparatus complies with Canadian ICES-003.
Cet appareil numérique de la classe A est conforme á la norme NMB-003 du Canada.

Safety Cautions

Prior to use of this product, review all safety markings and instructions.

CAUTION AVIS
RISK OF ELECTRIC SHOCK RISQUE DE CHOC ÉLECTRIQUE
DO NOT OPEN NE PAS OUVRIR

To prevent electric shock, do not remove the cover. There are no user-serviceable parts inside.
Internal adjustments are for qualified professionals only. Refer all servicing to qualified ser­vice personnel.

Pour prévenir un choc électrique, ne pas ouvrir le couvercle. Il n’y aucune pièces de rechanges
à l’intérieur. Tout ajustement interne doit être fait par une personne qualifié seulement.
Référez tout réparation au personnel qualifié.

Warning: This apparatus must be grounded.

This product is a safety class 1 product. There must be an uninterruptible safety earth ground
from the main power source to the product’s AC input. Whenever it is likely that the protection
has been impaired, disconnect the power cord until the ground has been restored.

Attention: Cet appareil doit être mise à la terre.

Cet appareil est de classe de sûreté 1. Il doit y avoir un ininterrompable de mise à la terre de
sécurité provenant de la source principale de courant de l’appareil de l’entrée du courant alter­natif. Quand la protection a été affaiblie, débrancher le fil de courant jusqu’à la mise à terre
a bien été réétablie.

Caution/Avis:

To prevent fire or shock hazard, do not expose this appliance to rain or moisture.
Pour prévenir feu ou choc électrique, ne pas exposé l’appareil à la pluie ou à l’humidité.

Caution/Avis:

For continued protection against fire hazard, replace only with same type/rating of fuse.
Pour poursuivre la protection contre le feu, replacez la fusible de même type/cote.

Warning/Attention:

There are some sharp edges inside. To reduce the risk of injury, do not remove cover.
Bord tranchant à l’intérieur. Pour réduire le risque de blessure, ne pas ouvrir le couvercle.

Note: Line Voltage Selector Switch

You will find the line voltage selector switch on the bottom panel. Before your model is shipped
from the factory, the switch is set to the power requirements of the destination. Nevertheless,
you should check that it is set properly before plugging the power cord into the wall outlet. If
the voltage requirements differ, adjust the selector switch as follows. Before adjusting, discon­nect the power cord.

1. Provide yourself with a medium size screwdriver.

2. Change the position of switch to the proper voltage for your area.

Do not expose this apparatus to drips or splashes.
Do not place any objects filled with liquids such as vases on the apparatus.
Do not install this apparatus in a confined space such as a bookcase or similar unit.
The apparatus should be located close enough to the AC outlet so that you can easily grasp
the power cord plug at any time.

4

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 10 for details.

What is a SmartMixer?

The AT-MX351 SmartMixer® is a microprocessor controlled, automatic switching, five-channel
mixer.

The four microphone inputs are XLRF-type balanced, with 48-volt phantom power available on
pins 2 and 3. The Aux input is an RCA jack accepting auxiliary-level input from sources such
as tape decks and VCRs. There is no signal processing of the Aux input. The mixer output is
XLRM-type balanced, non-inverting.

All AT-MX351 and AT-MX341a SmartMixers 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

The AT-MX351 provides an independent gain control on the front panel for each input channel.
Substantial gain reserve and adjustment range permit microphones of widely differing sensi­tivities to be used together successfully. Automatic threshold setting on all mic/line channels
ensures proper gating levels for existing ambient sound conditions.

Priority Pre-select

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 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.

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 40 dB if
desired. (See page 12, “Adjusting ‘Off ’ Attenuation.”)

If automatic switching is not desired, a “manual” DIP-switch setting on the front panel bypasses
the AT-MX351’s automatic switching and attenuation functions, causing the unit to behave
like a conventional mixer. In this mode, the relative level of each microphone is strictly a
function of the position of its respective front-panel gain control.

NOMA (Number of Open Microphones Attenuated)

The NOMA system helps control feedback by allowing for the increase in system gain that
occurs when the number of open microphones increases. A built-in matrix in the AT-MX351
recognizes exactly how many microphones are on and automatically adjusts the gain accord­ingly. Because use of NOMA is not always appropriate or desired, the AT-MX351 is shipped
with the NOMA function switched off.

5

AT-MX351 Front Panel

Gain 1 Gain 2 Gain 3Gain 4Aux In

AUTOMATIC MIXER

AT-MX351

Power

Selected Channel

Output Level

Priority Pre-select

1

2

3

4

Master

Lockout

-20

-10 -6

-3

0

+3

+6

Manual

Monitor

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. Aux In control. Adjusts input for source output level and/or operating conditions.

6. 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 10).

7. Priority Pre-select switches (1-4). 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.

8. Manual mode switch. Setting this switch in the “up” position bypasses all of the
SmartMixer’s automatic functions, except limiting and NOMA if selected.

9. Lockout LED indicator. Shows when lockout bus is active.

10. Master level control. Adjusts mixer output level for operating conditions.

11. Headphone output. 1/4” TRS jack.

12. Monitor headphone level control.

Figure 1. Front panel

10653

12

11987421

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