Lectrosonics FM870 User Manual

FM-AV4

PORTABLE WIRELESS SOUND SYSTEM

OPERATING INSTRUCTIONS

and trouble-shooting guide

LECTROSONICS, INC.

Rio Rancho, NM

INTRODUCTION

Thank you for selecting the FM-AV4 Portable Wireless Sound System. This system represents over 80
years of combined experience in the design of RF transmitters, receivers and Public Address systems. The
FM-AV4 sets new standards for operational convenience, flexibility and mechanical ruggedness. The built­in wireless receiver, the rechargeable power supply and the high quality of the audio output set this system
apart from any other portable PA system on the market.

This manual covers the FM870 RECEIVER, optional microphones and transmitters.

TABLE OF CONTENTS

INTRODUCTION .......................................... 1

GENERAL TECHNICAL DESCRIPTION .......................... 3

RECHARGEABLE BATTERIES ................................ 3

CONTROLS AND FUNCTIONS ................................ 4

M170 SERIES TRANSMITTERS ............................... 6

SYSTEM SETUP .......................................... 8

OPERATING TIPS ......................................... 10

OPERATING INSTRUCTIONS ................................. 11

MICROPHONE CHOICES .................................... 13

TROUBLESHOOTING ....................................... 14

ACCESSORIES AND REPLACEMENT PARTS .................... 15

SPECIFICATIONS ......................................... 16

SERVICE AND REPAIR ..................................... 17

RETURNING UNITS FOR REPAIR ............................. 17

WARRANTY ........................................ Back cover

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GENERAL TECHNICAL DESCRIPTION

The FM-AV4 Portable Wireless Sound System consists of an FM870 combination wireless
receiver/amplifier/speaker with a rechargeable battery pack, an M170 belt-pack transmitter and a
microphone. Optional microphones, transmitters and accessories are available. These items will be
discussed elsewhere in this manual.

The FM-AV4 features a VHF high band wireless microphone system with excellent operating range,
freedom from "dropouts" and interference from other radio transmissions. The built-in receiver provides
high selectivity and sensitivity with an automatic squelch circuit which requires no adjustment by the user.
The M170 belt-pack transmitter uses the microphone cord as the antenna which eliminates the dangling
wire antenna found on many other transmitters. The transmitter features a gain adjustment to perfectly
match your voice with the microphone.

The FM870 receiver/amplifier offers inputs and outputs to accommodate virtually any application. In
addition to the wireless, there is an auxiliary microphone input for dynamic microphones, a balanced,
microphone level audio output, and both "line in" and "line out" jacks for external tape recorders. This
allows the FM-AV4 to interface with other sound systems, video taping equipment or any type of "house"
sound system. This versatility lets you use the wireless microphone, a hard-wired microphone, a tape
recorder and the house sound system all at the same time.

The FM870 is powered by built-in rechargeable batteries and will easily operate for over 12 hours after an
overnight charge. The sound output will cover an audience of several hundred.

RECHARGEABLE BATTERIES

The battery pack in the FM870 is charged by plugging the supplied CH-40 charger into the jack labeled
CH-40 CHARGER INPUT on the control panel and moving the POWER switch to the CHARGE position.
Connect the charger into a standard 110 Volt AC outlet. The red POWER lamp beneath the switch will light
as long as the batteries are charging. There is no way to tell when the batteries are fully charged. To be
on the safe side, charge the battery 12-15 hours to be sure. The batteries should be charged after using
the system. You may leave the charger plugged in with no danger of damage to the system. They cannot
be overcharged. In fact, we recommend charging the system whenever it is not in use, then the system
will always be "ready to go".

2

CONTROLS AND FUNCTIONS

POWER/FUNCTION: A rotary switch which turns the power off and on and selects the operating mode.

OPERATE: Set in this position for normal use when the built-in speaker is to be used.

SPEAKER OFF: Set in this position for use with the FM870 plugged into the house sound system.

The wireless microphone will operate, but the sound from the built-in speaker will
be muted.

CHARGE: Set in this position to recharge the built-in battery pack.

POWER LED: A red LED indicates when the FM870 is turned on and the batteries are charged

up enough to operate the system. This LED will also light up when the batteries
are being recharged if the CH-40 charger is properly connected.

RF LED: A green LED lights when the companion transmitter is turned on and there is

sufficient signal for good system operation. Internal circuits monitor both signal
level and interference levels and decide if the transmitted signal is strong and
"clean" enough for satisfactory operation. If not, the RF lamp will go out and the
receiver will "squelch", shutting off the sound output. This action is automatic and
requires no user adjustment.

MODULATION: The -20 and LIMIT LEDs continuously indicate the modulation level (audio level)

of the received signal from the transmitter and are used when making initial
adjustments to the transmitter. See items 10 and 11 in the section on
"OPERATING INSTRUCTIONS" on page 10.

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CONTROLS AND FUNCTIONS cont’d

WIRELESS MIC
VOLUME: This control adjusts the volume of the built-in wireless microphone system. This

knob does not affect the MODULATION LEDs located near it.

AUX MIC/HI LEVEL
VOLUME: This control adjusts the volume of the AUX MIC INPUT and the HI LEVEL IN

inputs.

AUX MIC INPUT: This jack is a standard 1/4" phone jack and will accept a high impedance dynamic

microphone. It is recommended that you use the LECTROSONICS RM-121S
microphone with an MC-16C or MM-16 cord.

HI LEVEL OUT: An RCA phono jack that provides a one Volt output signal to drive line level inputs

of tape decks, cassette players and other P.A. systems.

HI LEVEL IN: An RCA phono jack input used for playback of line level outputs from tape decks,

cassette players and other P.A. systems.

MIC LEVEL OUTPUT: A 3-pin XLR audio connector which provides a balanced, low impedance (200

Ohm), 10 millivolt, microphone level output suitable for microphone mixers and
other units requiring a microphone level input. This balanced output also
provides the means to connect to the house sound system.

4

M170 SERIES TRANSMITTERS

Standard FM-AV4 systems include an M170 belt-pack transmitter which is designed to be used with a
lavalier or headset microphone. The optional M170-XLR transmitter (see page 6) is similar to the M170
but is equipped with two microphone connectors - a locking micro jack for lavalier or headset microphones
and an XLR connector for use with standard low impedance hand held microphones. If you have one of
the other optional Lectrosonics transmitters, consult the supplied manual for that transmitter for the
description and operating instructions.

The POWER ON/OFF switch, located on the side opposite the belt clip, turns the power on and off. The
switch should be left in the OFF position when the transmitter is not in use. The red LED above the on/off
switch indicates the condition of the battery. As long as this LED glows, even dimly, the battery is sufficient
to operate the transmitter.

The GAIN ADJUSTMENT matches the audio gain of the transmitter to different microphones, individual
voices, and other inputs. (see item 10 and 11 on page 10 in the section on OPERATING INSTRUCTIONS).

This adjustment is extremely important.

The BATTERY ACCESS THUMB SCREW is turned counterclockwise to remove the side cover to replace
the battery. The battery will only fit in one way. Observe the battery contact pad before inserting the
battery. The positive contact is the smaller one and fits into the compartment closest to the bottom of the
transmitter. Insert the battery contact end first, then push down the other end for a snug fit. To remove
the battery, push the exposed bottom edge of the battery with your fingernails toward the contacts and lift
it up and out.

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