Adjusting Off Attenuation, Preamp Outputs

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 “VR3” (Figs. 4 and 5, page 11). 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, VR9 and VR12 control “off ” attenuation for channels 2, 3 and 4 respectively.

Changing the settings of the switches designated on the circuit board by “SW5,” “SW11,” “SW17” and SW23” will extend the range of “off ” attenuation to –40 dB for channels 1, 2, 3 and 4 respectively.

Preamp Outputs

Each microphone channel has an independent unbalanced preamp output that is separate from the main mixer output. This is helpful when it is necessary to record the output of each channel, whether or not it is the active mixer output (as is required, for example, in some courtroom proceedings). As set at the factory, no gating is applied to these outputs. To gate these outputs, unplug the unit, remove the top cover and locate the switches designated on the circuit board by “SW6,” “SW12,” “SW18” and SW24” (Figs. 4 and 5, page 11). Change the switch position(s) to “Gating” for channels 1, 2, 3 and/or 4 respectively, as desired.

Input Limiters

Independent, adjustable limiters are available on all mic channels. To adjust the limiter threshold of channel 1, unplug the unit, remove the top cover and locate the trimpot designated on the circuit board by “VR2” (Figs. 4 and 5, page 11). It is factory set at approximately 0 dB RMS. When the control is turned fully counter-clockwise, limiter threshold is approximately –10 dB RMS. Conversely, when the adjustment is turned fully clockwise, limiter threshold

is approximately +10 dB RMS. VR5, VR8 and VR11 adjust limiter threshold for channels 2, 3 and 4 respectively.

Changing the settings of the switches designated on the circuit board by “SW4,” “SW10,” “SW16” and SW22” will turn off the threshold-limiting function on channels 1, 2, 3 and 4 respectively.

Force-on/Force-off

To activate force-on/force-off, install a closure between the appropriate pin and Ground Reference on the External Control connector on back of unit.

External Control Connector Pinout

Pin 1	Channel 1 force off	Pin 8	Channel 4 force on
Pin 2	Channel 2 force off	Pin 9	Channel 1 TTL out

Pin 3	Channel 3 force off	Pin 10	Channel 2 TTL out

Pin 4	Channel 4 force off	Pin 13	Ground reference
Pin 5	Channel 1 force on	Pin 14	Channel 3 TTL out
Pin 6	Channel 2 force on	Pin 15	Channel 4 TTL out
Pin 7	Channel 3 force on

AT-MX351 specifications

The Audio-Technica AT-MX351 is a versatile mixer that has gained a strong reputation amongst audio professionals for its performance and utility. Designed for various applications, from live sound to permanent installation, the AT-MX351 boasts features that enhance audio quality and ease of use.

One of the standout features of the AT-MX351 is its ability to handle multiple audio sources with ease. It features three programmable microphone inputs, making it perfect for settings where multiple speakers or performers are involved. This is especially useful in conference rooms, lecture halls, and places of worship, where different users may need to take turns speaking without the hassle of connecting and disconnecting microphones.

The mixer is equipped with advanced automatic mixing technology, which intelligently manages the audio levels from various microphones. This prevents feedback and minimizes background noise, resulting in clear and intelligible sound. The AT-MX351 utilizes Audio-Technica's proprietary Automatic Gain Controls (AGC) to ensure that the audio levels remain consistent, providing a professional sound experience.

In terms of connectivity, the AT-MX351 features balanced XLR inputs, allowing for secure connections that maintain audio integrity. It also includes unbalanced line inputs, catering to a wider array of equipment. The mixer offers both balanced and unbalanced outputs, providing flexibility for integration into different sound systems.

Another notable characteristic of the AT-MX351 is its user-friendly interface. The layout of the controls is intuitive, allowing operators to make quick adjustments on the fly. The clear LED indicators help users monitor signal levels easily, making it easier to identify any issues. This is particularly beneficial during live events where quick decision-making is crucial.

The AT-MX351 also incorporates a built-in limiter and compressor, which help to avoid distortion and maintain a consistent sound quality. This feature is especially important in environments with varying acoustic dynamics or when dealing with powerful audio signals.

In summary, the Audio-Technica AT-MX351 mixer stands out due to its robust features, including multiple programmable microphone inputs, advanced automatic mixing technology, and user-friendly controls. This combination of technology and usability makes it an ideal choice for audio professionals seeking reliability and high-quality sound in their applications. Whether for live performances, conferences, or installations, the AT-MX351 proves to be a reliable and effective solution in the audio mixing landscape.