3M A121 User Manual

Noise Reduction Module

Model A121

Installation Instructions

Description

The 3M Noise Reduction Module (3M part number 78-9236-6403-7) improves the inbound intelligibility of an
intercom system by reducing environmental background noise from vehicles, airplanes, noisy intersections, etc.

Additional Material Required

• 18 - 22 AWG twisted - shielded pair audio wire

• 2 mounting screws and appropriate wall anchors

Important: The 3M Noise Reduction Module should be mounted no more than 3 feet from the intercom or base
station.

System Requirements

The 3M Noise Reduction Module requires a system with a separate outside microphone and speaker. The A121 will
not function with an intercom system configured to use a single speaker as both the microphone and speaker. The
A121 will work in conjunction with most dynamic microphones and speaker/microphone assemblies.

System Configuration

The 3M Noise Reduction Module configuration is controlled by two jumper switch (JMP1 and JMP2) settings.
JMP1 is used to set the appropriate gain for the MENU MICROPHONE.
JMP2 is used to match the A121 output level to the input of the intercom system.

Jumper
Position

JMP1

JMP2

Table 1. 3M Noise Reduction Module Jumper Settings

* Separate microphone
& speaker at menu
sign/post
* 3M Intercom HME Intercom

Position A Position B

Do not use this position

Note: * Indicates factory default settings

Mode Configuration

The 3M Noise Reduction Board can be configured in several different modes by setting DIP switch, SW2.
Following is a brief description of each mode and a DIP switch setting table.

Noise Reduction: With SW2 number 1 ON, the inbound microphone voice signal is digitized. The noise is

digitally removed from the voice and converted back to an analog voice signal. The analog voice signal is
then sent to the microphone input of the intercom.

Echo Reduction: With SW2 number 2 ON, echo is reduced for full-duplex intercom systems. Set SW2

number 2 OFF for half-duplex systems.

Restaurant/Truck Stop Noise Reduction Level: With SW2 number 3 OFF, the A121 is set for restaurant noise

reduction level. With SW2 number 3 ON, the A121 is used for truck stop noise reduction level, which
provides more noise reduction with slightly more voice degradation.

Hi Frequency Equalization: With SW2 number 4 ON, the higher-end frequencies are increased by 3 dB. This

should be set to the customer’s preference.

SW2

ON Position OFF Position

Number

1 *Noise Reduction ON

(Normal Mode)

Test Mode

(Factory use only; do not change.)
2 *1Echo Reduction ON Echo Reduction OFF
3

4

2

Truck Stop Noise

Reduction Level

2

Hi Frequency Equalization

*2Restaurant Noise

Reduction Level

*2Hi Frequency Equalization OFF

ON

5 Not Used Not Used

Notes: * Indicates factory settings.

1

Must be ON for 3M, HME, and Panasonic Full Duplex Systems

2

Set to customer preference.

Table 2. 3M Noise Reduction Module SW2 Settings

Status Indication Table

The condition of the red LED on the 3m Noise Reduction Module indicates the current status of the unit. The LED
can be off, blink at defined intervals, or be constantly lit Table 3 illustrates the status indicated by the LED.

Status LED

Power OFF LED off.
Normal Mode LED blinks once per second.
Test Mode LED blinks three times per second.
Fault Condition LED is solid red (constantly illuminated).

Table 3. 3M Noise Reduction Module Status Indication

Final Checkout Procedure

1. Turn the ON/OFF switch of the A121 ON. The red LED should blink slowly. Listen for a reduction in the
background noise.

2

2. If the A121 is in a half-duplex system, set SW2 number 2 OFF and proceed to step 3.
If the A121 is in a full-duplex system set SW2 number 2 OFF. Speak into the headset mic or intercom mic.
The echo should increase. Turn SW2 number 2 back ON. The echo should decrease.

3. Set SW2 number 3 for appropriate level of noise reduction. Set SW2 number 3 OFF for restaurant mode . Set
SW2 number 3 ON for truck stop mode.

4. Set SW2 number 4 (Hi Frequency Equalization) to customer’s preference.

Troubleshooting

Problem Possible Cause Correction

1. Status fault indicated. Inbound audio exceeded maximum

Switch A121 off for one second.

level.

2. No inbound audio. Mode setting is incorrect.
Wiring is incorrect.

Check mode configuration.
Check wiring.

3. No outbound audio. Wiring is incorrect. Check wiring.

4. Loud audio in 3M

headset when headset user

Inbound audio on 3M base station too
low.

talks.

5. Excessive echo Excessive feedback from menu
speaker to menu mic.

Increase MENU MIC SENS
potentiometer. Headset user should
then reduce the headset audio volume.

Add extra acoustic insulation to menu
mic chamber.

Table 4. A121 Noise Reduction Module Troubleshooting

Wiring Diagrams

3M Base Station

MIC
MIC

SHIELD
MENU SPKR
MENU SPKR

AUDIO OUT

ALT ALERT

VEH DET

ALERT OUT

12V UNREG

MIC OUT
MIC OUT

MENU SPKR
MENU SPKR

MENU

1

MIC IN MIC OUT

2

SHLD SHLD

3

MENU

4

SPKR
MENU

55

SPKR

INTERCOM

MIC OUTMIC IN

MENU
SPKR

MENU
SPKR

1

2

3

4

A121 Noise Reduction Module

Figure 1. Wiring for 3M C760/960/1060 Base Station

Menu Post

MENU
MIC

MENU
SPKR

3