Lectrosonics FM875 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 FM875 RECEIVER, optional microphones and transmitters.

TABLE OF CONTENTS

INTRODUCTION .......................................... 2

GENERAL TECHNICAL DESCRIPTION .......................... 4

RECHARGEABLE BATTERIES ................................ 4

CONTROLS AND FUNCTIONS ................................ 5

TRANSMITTERS .......................................... 7

SYSTEM SETUP .......................................... 9

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

2

GENERAL TECHNICAL DESCRIPTION

The FM-AV4 Portable Wireless Sound System consists of an FM875 combination wireless
receiver/amplifier/speaker with a rechargeable battery pack, an M175 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 M175 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 properly
match the level of your voice and the microphone.

The FM875 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 "aux 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 FM875 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 people.

RECHARGEABLE BATTERIES

It is very important to recharge the battery pack immediately after the unit is used. The battery pack is
charged by plugging the CH-40 charger into the jack labeled CHARGE on the control panel of the unit.
Connect the charger into a standard 110 Volt, 60Hz AC outlet. The green lamp beneath the jack will light
as long as the batteries are charging. When the batteries are almost completely charged the green charg­ing light will go out. You may leave the charger plugged in after the green light has gone out with no
danger of damage to the system. In fact, we recommend charging the system whenever it is not in use,
then the system will always be "ready to go".

Operation is possible while charging the batteries with the supplied CH-40 charger, however since the
amplifier consumes more power than the CH-40 charger can supply, the batteries will recharge faster if you
turn the amplifier power off while charging.

The battery pack should be recharged for 16 hours at least once every six months even when the unit is
in storage and not being used.

In many cases, a battery that seems to be dead may be saved by prolonged charging. As much as 10
days of continuous charging may be necessary to restore the batteries after they have been left for several
weeks or more in a "discharged" condition. The charge lamp may not light up during the first part of a
prolonged charging period.

3

CONTROLS AND FUNCTIONS

CHARGE UNTIL GREEN LED

GOES OUT OR LONGER

CHARGE

WIRELESS MIC

RF

ADJUST MIC GAIN ON TRANSMITTER

UNTIL LIMIT LED FLASHES ON VOICE PEAKS

–20

LIMIT

MODULATION

2

VOLUME

4

0

MIC OR AUX

6

8

10

IN

LECTROSONICS

(Items are listed in right to left order as shown on the panel above.)

POWER: A toggle switch which turns the power off and on.

CHARGE: Jack for CH-40 charger.

POWER LED: A red LED indicates when the FM875 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. This led will go
out when the batteries are discharged.

2

AUX

VOLUME

4

0

MIC LEVEL

OUT

OUTPUT

2

6

10

AUX

8

LINE

IN

LO-Z

BAL

OMNI–BUS

3

1

IN/OUT

POWER

CHARGE LED: Lights when the unit is being charged. This green led will go out when the

batteries are fully charged.

OMNI-BUS IN/OUT: An RCA phono jack that functions both as a line level input and line level output.

This "omnibus" jack is primarily used for interconnecting several FM875s together
for simultaneous operation. This jack can also be used with a tape deck to either
record from or play back into the FM875. When used with a tape deck or other
audio source, the sound output level must be controlled by the volume control on
the tape deck since there is no volume control on the FM875 for this jack.

Male

FM 875 #1 FM 875 #2

– –

OMNI BUS

IN/OUT

RCA

Connect two FM875s

together using the

OMNI-BUS jacks.

Male
RCA

OMNI BUS

IN/OUT

When connected in this manner, the volume control knob on one unit will affect

the loudness of that source (wireless, aux, etc.) on both FM875 systems.

4

MIC LEVEL
OUTPUT:

LINE OUT:

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

AUX VOLUME: This control adjusts the volume of the MIC OR AUX IN and the AUX IN inputs.

MIC OR AUX IN: This jack is a standard 1/4" phone jack and will accept a dynamic microphone.

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

A 3-pin XLR audio connector which provides a balanced, low impedance (200
Ohm), 10 millivolt, microphone level output suitable for house sound systems,
microphone mixers and other units requiring a microphone level input. Pin 1 is
Ground or Shield, pin 2 is Audio High, and pin 3 is Audio Low. If using an
unbalanced load, pin 1 is Ground, pin 2 is Audio and pin 3 is not used. The output
level at this jack varies with the setting of the WIRELESS MIC VOLUME and AUX
VOLUME knobs.
An RCA phono jack that provides a 1 Volt output signal to drive line level inputs of
tape decks, cassette players and other P.A. systems.

cassette players and other P.A. systems.

This

knob does not affect the MODULATION LEDs located near it.

MODULATION LEDs: 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.

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.

5

TRANSMITTERS

Standard FM-AV4 systems include an M175 belt-pack transmitter which is designed to be used with a
lavalier or headset microphone. If you have one of the other optional Lectrosonics transmitters, consult
the supplied manual for that transmitter for the description and operating instructions.

The MIC JACK is a locking micro jack that supplies "phantom power" for electret microphones such as the
Lectrosonics M130, M140 and the HM142V and HM152V headset models. Insert the microphone cord plug
into the jack and rotate it clockwise to lock it. It is important that the plug be securely locked, since the
microphone cord serves as the antenna for the transmitter.

The POWER ON/OFF switch turns the power on and off. The switch should be left in the off position when
the transmitter is not in use. When the switch is in the on position, the battery will be drained even though
the transmitter is not being used.

The BATTERY INDICATOR LAMP will light when the transmitter is turned on and will stay lit as long as
the battery is good. As the battery voltage drops, the lamp will grow dim and finally go out.

The MIC LEVEL is a recessed screwdriver adjustment used to match the gain of the transmitter to different
microphones, individual voices or other audio inputs such as tape deck outputs.

The AUDIO MUTE SWITCH (M175-LS only) is a toggle type on-off switch used to shut off the audio signal
without shutting off the RF carrier of the transmitter.

LECTROSONICS

M175

ON

PWR

OFF

+

MIC

LEVEL

–

MIC

Audio Switch

Battery Indicator Lamp

Power ON/OFF Switch

Mic Level Adjust

Microphone Jack

Belt Clip

M175 Series

AUDIO

OFF

ON

PWR

OFF

+

MIC

LEVEL

–

MIC

LECTROSONICS

M175-LS

6