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

Figure 2. Wiring for 3M C760/960/1060 Base Station with Interconnect Module

4

3M Base Station

MIC
MIC

SHIELD
MENU SPKR
MENU SPKR

A121 Noise Reduction Module

MENU INTERCOM

MIC IN MIC OUT

1

2

SHLD SHLD

3

MENU

4

SPKR
MENU

55

SPKR

MIC OUTMIC IN

MENU
SPKR

MENU
SPKR

1

2

3

4

Menu Post

AUDIO OUT

ALT ALERT

VEH DET

ALERT OUT

COM

12V UNREG

To Vehicle Detector

Figure 3. Wiring for 3M C760/960/1060 Base Station with 3M Audio-Level Control Module

A121 Noise Reduction Module

MENU INTERCOM

1

MIC IN MIC OUT

2

3

SHLD SHLD

MENU

4

SPKR
MENU

55

SPKR

MIC OUTMIC IN

MENU
SPKR

MENU
SPKR

1

2

3

4

MIC OUT COM

MIC OUT

SHLD SHLD

VEH DET MIC IN

COM MIC IN

AUDIO IN

MENU

SPKR

3M Audio-Level Control

3M D15/D30 Intercom

MIC
MIC
SHIELD

SPEAKER

SPEAKER

MENU
SPEAKER

MENU
MIC

Menu Post

MENU
MIC

MENU
SPKR

Figure 4. Wiring for 3M D15/D30 Intercom

5

C921AA Base Station

A300 Audio Greeter Optional Service Timer

MIC
MIC

SHIELD

MENU SPKR

MENU SPKR

MON SPKR

COM

AUDIO IN

AUDIO OUT

ALT ALERT

VEH DET

ALERT OUT

COM

12V UNREG

TIMER TRIG

COM

MSG4 TRIG

VEH DET-

VEH DET+

COM

MUSIC
MUSIC

COM
_____
TALK

AUDIO OUT

J9

INTERCOM SPKR
INTERCOM SPKR

COM

INTERCOM MIC
INTERCOM MIC

MENU SPKR
MENU SPKR

COM

MENU MIC
MENU MIC

J10

12
11
10
9
8
7
6
5
4
3
2
1

10
9
8
7
6
5
4
3
2
1

MENU SPKR
MENU SPKR

MIC

MIC
MENU SPKR
MENU SPKR

MIC OUT
MIC OUT

COM

VEH DET

AUDIO IN

A121 Noise Reduction Module

MENU

INTERCOM

1

MIC IN MIC OUT

2

3

SHLD SHLD
MENU

4

SPKR
MENU

5

SPKR

1

2

MIC OUTMIC IN

3

MENU

4

SPKR
MENU

5

SPKR

Menu Post

MENU
SPKR

MENU
MIC

VEHICLE

DETECTOR

Figure 5. Wiring for 3M C760/960/1060 Base Station with A300 Audio Greeter

6

Menu Post

MENU MIC

MENU SPKR

Panasonic WX-C510/WX-C1010

Base Station

H

SP/MIC SP DET 12VAC

C
GND

MIC

C
H

A121

Noise Reduction Module

MENU INTERCOM

1

MIC IN MIC OUT

2

3

SHLD SHLD

MENU

4

SPKR

MENU

55

SPKR

MIC OUTMIC IN

MENU
SPKR

MENU
SPKR

1

2

3

4

H
C

H
COM
GND
AC
AC

Figure 6. Wiring for Panasonic WX-C510/WX-C1010 Base Station

HME SYS2500/DS/DSL

Base Station

A121 Noise Reduction Module

MENU INTERCOM

MIC IN MIC OUT

1

2

SHLD SHLD

3

MENU

4

SPKR

MENU

55

SPKR

MIC OUTMIC IN

MENU
SPKR

MENU
SPKR

1

2

3

4

Figure 7. Wiring for HME SYS2500/DS/DSL Base Station

MIC/SPKR
MIC/SPKR
SHIELD

OUTSIDE SPKR
OUTSIDE SPKR

*

*

*

Needed for HME

"Hands Free" system

Menu Post

MENU
MIC

MENU
SPKR

7

Audio Greeter

TIMER TRIG

MSG4 TRIG

AUDIO OUT

INTERCOM SPKR
INTERCOM SPKR

INTERCOM MIC
INTERCOM MIC

MENU SPKR
MENU SPKR

3M A300

COM

VEH DET-

VEH DET+

COM

MUSIC
MUSIC

COM

_____

TALK

J9

COM

COM
MENU MIC
MENU MIC

J10

** Note:

Set A300 vehicle detector
trigger polarity to negative (set
SW2 number 3 OFF and
JMP1 to Position B).

12

Terminals 6 and 9 may also
be used for a contact-closure

11

connection.

10

** VEH DET SIG

9
8
7

VEH DET GND

6
5
4
3
2
1

10

WHITE
GREEN

9

8

SHLD

7

BLACK

6

RED

5

MENU SPKR

MENU SPKR

4
3
2

MIC OUT
MIC OUT

1

VEHICLE

DETECTOR

GND
OUTPUT

*

3M A121 Noise Reduction Module

MENU

INTERCOM

MIC IN MIC OUT

1

2

3

SHLD SHLD
MENU

4

SPKR
MENU

55

SPKR

1

2

MIC OUTMIC IN

3

MENU

4

SPKR
MENU

SPKR

Menu Post

MENU
MIC

MENU
SPKR

5
6

SYS2500D/DS/DSL

7
8
9
10
11
12
13
14

Base Station

SHLD

BLACK

RED

J1

4
5

VEH DET SIG

6

VEH DET GND

7

RED

8

BLACK

9

WHITE

10

GREEN

J7

HME

SPKR/MIC

OUTSIDE
SPEAKER

Figure 8. Wiring for HME SYS2500D/DS/DSL Base Station with 3M A300 Audio Greeter

8

HME MR100A

Message Repeater

MENU SPKR
MENU SPKR

GND (SHIELD)

MENU MIC
MENU MIC

BASE SPKR CONN

BASE SPKR CONN

GND (SHIELD)
BASE MIC CONN
BASE MIC CONN

VEH DET IN

VEH DET OUT

ENABLE/DISABLE

EXT PLAY CANCEL

GND

Menu Post

MENU

MIC

MENU
SPKR

6

MENU SPKR

7

MENU SPKR
8
9
10

WHITE

11

GREEN

12
13

SHLD
14

RED
15

BLACK

VEH DET SIG

16

17
18
19

VEH DET GND

20

MIC OUT
MIC OUT

VEHICLE

DETECTOR

GND
OUTPUT

5
6

SYS2500D/DS/DSL

7
8
9
10
11
12
13
14

Base Station

SHLD
BLACK

SPKR/MIC

RED

HME

J1

4
5

VEH DET SIG

6

VEH DET GND

7

RED

8

BLACK

9

WHITE

OUTSIDE

GREEN

J7

SPEAKER

10

MENU

MIC IN

1

2

MIC IN

SHLD

3

MENU

4

SPKR
MENU

5

SPKR

INTERCOM

MIC OUT

MIC OUT

SHLD
MENU

SPKR
MENU

SPKR

1

2

3

4

5

3M A121 Noise Reduction Module

Figure 9. Wiring for HME SYS2500D/DS/DSL Base Station with HME MR100A Message Repeater

3M Commercial Care Division

Food Services trade Department

3M Center
St. Paul, MN 55144-1000 78-6912-0699-5 Rev. E

© 3M 2006 May

9