MR-1 02A

Remote Headset

Station

INSTRUCTION and

SERVICE MANUAL

945 Camelia St. Berkeley, California 94710 510-527-6666

Clear-Com 810033 8/15/88 REV. B

CLEAR-a0M MR-102A REMOE INTERCOM STATION

OPERATION MANUAL

CONTENTS PAGE

Introduction to the Remote Station .............. 1

System ............................. 3

Headsets ................................ 4

Operating Controls .............................. 5

Technical Theory of Operation ................... 6

Parts Listing 7

Specifications ................................ 7

ILLUSTRATIONS

2-Channel Interconnect Wiring ................... 2

MR-102A Mounting Dimensions .................... 3

Headset "Y" Cable ............................... 4

Headset Extension Cord .......................... 4

MR-102A Block Diagram .......................... 6

Schematic ................................ 8 ff0 CE.:

While Clear-Com makes every attempt to maintain the accuracy of the information contained in its product manuaJs, the information is subject to change without notice.

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DOCUMENTATION ADDENDUM

MR-102A MANUAL

REV.A

No-;ember 17, 1987

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MIC TO LINE GAIN LEVEL INCREASE

In effectina a 4dB Mic to Line increase i.n gain level, the following changes have been made:

Change: lSOR OHM

330pf

39f

At:

R5, E8

C7

C8

To:

270K OHM i50pf

27?f

I. INTRODUCTION TO THE MR-102A REMOTE STATION

The MR-102A Remote Intercom Station allows two-way (talk/listen) commu- nicating on two separate chan- nels. It features our "contoured" frequency response for excellent speech intelligibility in high- and low-noise environments. The MR-

102A works with a standard dynamic headset, which it drives to levels greater than 110 dB SPL (the unit can support two dynamic headsets if they are connected with a Y-cord, described later in this manual).

A recessed sidetone control is included on the MR-102A front pan- el. It enables the operator to adjust his/her own voice level as heard in the headset. The station also features Visual Call Signal- ling to attract the attention of other intercom operators and to activate the remote paging func- tions at speaker stations. ai

W The MR-102A is designed for perma- nent installation in a standard two gang outlet box. The front panel is a charcoal-brown, brushed aluminum wall plate, with the intercom electronics module mounted on the back. Only 1.75" depth is required for installation.

The MR-102A connects to the intercom system with standard shielded cable. It provides a clearlylabelled, 5-pin terminal strip for intercom and power input. In places where conduit is present, or where AC interference is not a problem, you may interconnect stations with unshielded wire or unshielded cable.

Bidirectional current sourcing, high impedance bridging, and low current drain allow up to 100 MR-

102A or other headset stations to be connected over one mile of cable with one Main Station/Power Supply to support the system.

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II. INSTALLATION OF THE MR-102A

* The MR-102A connects to the inter- com system via a five-screw terminal strip (designated on the Sche- matic as "H-1i). While making con- nections, refer to the stick-on label adjacent to the terminal strip on the back of the MR-102A panel; it identifies each pin by number and assignment, as shown below:

C-H. I

CH 1+30D assignments:

1--Chassis Ground

2--Intercom Audio/Channel A

3--Intercom Audio/Channel B

4--DC, +30 volts

5--Common

-chassis

To prevent ground loops and buzzes, the common terminal (pin 5) should

NEVER be directly connected to ground (pin 1). Use conduit or a separate wire to interconnect two or more MR-102A panels.

Designed for permanent installation, the MR-102A mounts readily in a standard 2-gang electrical outlet box, minimum depth 1-3/4". Refer to

Figure 1, Interconnect Wiring, when deciding how to install the unit.

If you plan to use only one channel on the MR-102A, disable the Channel Select switch by jumping Channels A and B together on the connector block, and hook the intercom audio line to either terminal.

After preparing a surface for installation, route standard two-

* conductor, shielded cable from a

Main Station/Power Supply output connector to the MR-102A's loca- tion. Connect wire to the termi- nals according to the following pin

A diode in the DC input of each

Remote Station protects the circuitry against miswiring in the interconnect cables. The Remote Station bridges the terminated audio line with approximately 20k ohms.

MP-102

MOUNTING DIMENSIONS

Figure2

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OVERALL,

MIN/MUM DEPTH,

'75'

1 375

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III. HEADSErS

The MR-102A provides a 4-pin, male

XLR connector for a dynamic head- set.

Its built-in headset amplifier can drive one headset to levels greater than 110 dB SPL. The mic preamp automatically shuts off when the headset is disconnected, thereby eliminating hum pick-up and extra- neous noise.

The headset connector pin-out as- signment is:

Pin 1: Mic Ground

Pin 2: Mic Hot

Pin 3: Headphone Ground

Pin 4: Headphone Hot

To assure proper level and perfor- mance, the dynamic headset should have the following characteristics:

Microphone type: dynamic

Impedance: 150-250 ohms

Output level: -55 dB

Headphone type: dynamic

Output impedance: 300-2000 ohms

Figure 3: HEADSET r-CABLE CONNECTIONS

The MR-102A drives two dynamic headsets with only a slight reduction in level. Clear-Corn can supply you with Model YC-100 "Y" ter Cable, which allows you to plug two headsets into the one 4-pin connector on the front panel.

Alternately, you may construct your own Y-cable; we recommend you use

Belden 8416 (2-conductor, 25 gauge) or Belden 8734 (3-conductor, 22 gauge); see Figure 3.

If desired, you may construct an extension cord for your dynamic headset., using the same cable specified above (see Figure 4). Limit the extension to 15 feet or less; greater lengths lead to possible capacity coupling between the mic signal and the headset signal, which would cause oscillation or a loss in frequency response.

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PIN 1: UIC GROUND

PIN 2: MIC HOT

PIN 3: HEADPHONE GROUND

Pin 4: HEADPHONE HOT

CAUTION: DO NOT CONNECT

MIC GROUND & HEADPHONE

GROUND TOGETHER

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Figure 4: HEADSET EXTENSION CORD is OR LESS

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IV. MR-102A OPERATING CONTROLS

S

A/B Chan. Select

This two-position toggle switch selects which channel will be used for communicating.

Volume

This knob adjusts the listen-level in the headset.

Sidetone Adj.

The MR-102A provides a Sidetone control which enables the operator to adjust the level of his/her voice as heard in the headset, allowing up to 35 dB reduction of acoustical pick-up. You need only adjust the leave the intercom system. Adjusting the sidetone does not affect the level of incoming or outgoing signals.

The sidetone control is inside an unmarked hole located above the

Volume control. The sidetone adjustment is accomplished with a smallbladed screwdriver. At the factory, Clear-Com sets the sidetone to be approximately 6 dB lower than the incoming signals.

Adjust sidetone in the following manner:

*

1) plug in headset

2) turn on mic

3) turn up volume all the way

4) insert screwdriver through front panel hole and engage the slot on the internal trimpot

5) begin talking while slowly turning the screwdriver. When you can barely hear yourself, you'll have found the null point.

Off/Mic-On/Call

This 3-position toggle switch provides three functions. In the up position, the mic in your headset is "off". In the middle position, the mic is on.

The third position, Call, is associated with the Visual Signal Circuitry that's standard on Clear-Con equipment. It allows the intercom user to attract the attention of operators who have removed their headsets. Signalling other stations is accomplished by momentarily pressing the switch down to the Call position. Signalling follows the position of the Channel Select switch; for instance, if you are on

Channel A, signalling activates the call lights on all stations that are assigned to that channel.

*

Call Light

The amber lamp on the MR-102A will light up when another station (which is using the same channel as the MR-102A) activates the Call circuit, or when you are calling other stations. If it is necessary to replace the light, unscrew the lens cap and remove the bulb; its replacement is a #387 bulb.

V. THEORY OF OPERATION

The MR-102A incorporates Clear-

Com's high-impedance bridging meth- od, so it connects to the system without taking appreciable power from the line. This enables up to

100 MR-102A's to be connected in one system with only a 6 dB loss in level.

Each Remote Station consists of 3 basic circuits: the listen circuit, the talk circuit (including side- tone) and the signalling circuit.

In the LISTEN circuit, signals from the line and the mic pre-amp go to the buffer amp (where signals are amplified 10 dB), then to the vol- ume control, and then to the head- set amp for a final 38 dB of gain.

Current-limiting in the headset amp protects it from shorts.

In the TALK circuit, signals from the mic are amplified 37 dB by a low-level pre-amp. Preamplified signals are sent to the audio line

(where they're attenuated by 17 dB) and to the line buffer amp. The line buffer feeds part of the sig- nal back to the bridging circuit, raising the line impedance to 20k ohms. When the mic is turned off, the mic pre-amp gain is reduced to

MR-102A BLOCK DIAGRAM unity, reducing any noise in the input circuitry by 30 dB.

The SIDETONE control works by injecting a portion of the audio signal from the mic into the buffer amp. The mic pre-amp signal feeds through the sidetone volume control and to the inverting input of the buffer amp. Cancellation occurs when the mic signal on the line and the signal from the sidetone control are mixed into the buffer amp.

The cancellation can be varied from full on to a 35 db null.

The visual CALL SIGNAL is accomplished by impressing a DC voltage on the audio line. Pressing "Call" turns on a transistor, applying about 11 volts to the audio line.

This voltage goes to all Stations on the same channel, where the DC is detected by a high gain amp that turns on the Call light. The callreceive circuit requires only 4 volts from the line to turn on the light. The 7-volt difference between the send and receive voltages assures positive signalling, even on very long lines. Various capacitors block DC call voltages from entering the amp circuits.

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VI. PARTS LISTING

Part #

710030

Description

Printed Circuit Module

Qty.

1

210013 Connector, dynamic headset 1

240014 Volume knob, 3/44" black 1

390000 Lamp cover, amber

390001 Light bulb, #387

510004 Switch, toggle, 3-pos

510040 Switch, toggle, 2-pos

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Schematic Ref. Des.

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VII. MR-102A SPECIFICATIONS

AMPLIFIER DESIGN

Solid-state, integrated circuit amps (which include a mic preamp, headset power amp and signalling circuit). Current-limited with short-circuit & reverse polarity protection.

.

MIC PREAMPLIFIER

Frequency Response: 250 Hz-12k Hz,

GENERAL SPECS

Line Level: -15dBv max* contoured to enhance Sidetone Adj.: 35dB null to full on intelligibility

Mic Input Impedance: 200 ohms

Call Voltage: 11 VDC on audio line

Call Light Sensitivity: 4 volts

Signal-to-Noise: 75dBv* Mic Preamp Gain: 37dB

Max. Input before Clipping: -34dBv* Equivalent Input Noise: 12ldBv*

Station Bridging

Impedance: 20k ohm (200-10k Hz) HEADPHONE AMPLIFIER

Freq. Response: 150-18k Hz, 42 dB

Load Impedance Range: 300-2000 ohms

Output Level: +20 dBm, 26v p-p

Headset Level:

@ 600 ohms

>110 dB with standard Clear-Com headsets

Distortion:

Amplifier Gain:

0.2% THD at 1k Hz

38dB

Power Required:

15 ma talking

55 ma signalling

Voltage Range: 12-32v, 28v nominal

CONNECTORS

10 ma quiescent,

Dynanic Headset: 4-pin, XLR, male

Line: 5-screw terminal block

'OdBv is referenced to 0.775 volts RIS.

PHYSICAL CHARACTERISTICS

Dimensions: 4.5" (11.3 cm) square

Rear Depth:

Weight:

1.75" (4.38 cm)

7.25 oz. (.21 kg)

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