Lectrosonics LMa User Manual
LMa
Synthesized UHF Belt-Pack Transmitter
INSTRUCTION MANUAL
Featuring
Digital Hybrid Wireless® Technology
US Patent 7,225,135
Fill in for your records:
Serial Number:
Purchase Date:
Rio Rancho, NM, USA
www.lectrosonics.com
LMa
2
LECTROSONICS, INC.
Frequency-Agile UHF Belt-Pack Transmitter
Table of Contents
Introduction .............................................................................................................................................................................................4
Digital Hybrid Technology .....................................................................................................................................................................4
Frequency Agility...................................................................................................................................................................................4
Wide-Band Deviation ............................................................................................................................................................................4
Long Battery Life ...................................................................................................................................................................................4
Servo Bias Input and Wiring .................................................................................................................................................................4
Input Limiter ..........................................................................................................................................................................................5
No Pre-Emphasis/De-Emphasis ...........................................................................................................................................................5
Pilot Tone Squelch ................................................................................................................................................................................5
Circulator/Isolator ..................................................................................................................................................................................5
LMa Block Diagram ...............................................................................................................................................................................5
Controls and Functions .........................................................................................................................................................................6
Input Jack ..............................................................................................................................................................................................6
Power ON/OFF Switch .......................................................................................................................................................................... 6
Power LED ............................................................................................................................................................................................ 6
Frequency Select Switches ...................................................................................................................................................................6
Modulation LEDs ...................................................................................................................................................................................6
Audio Level ...........................................................................................................................................................................................6
Antenna .................................................................................................................................................................................................6
Belt Clip .................................................................................................................................................................................................6
Battery Installation .................................................................................................................................................................................7
Operating Instructions ...........................................................................................................................................................................8
Selecting the Compatibility Mode ..........................................................................................................................................................8
Attaching a Microphone or Musical Instrument and Adjusting Audio Levels .........................................................................................8
Adjusting the Frequency .......................................................................................................................................................................9
5-Pin Input Jack Wiring ........................................................................................................................................................................10
Installing the Connector: .....................................................................................................................................................................10
Microphone Cable Termination
for Non-Lectrosonics Microphones .............................................................................................................................................11
Wiring Hookups for Different Sources ...............................................................................................................................................12
Compatible Wiring for Both Servo Bias Inputs and Earlier Transmitters: ............................................................................................12
Simple Wiring - Can ONLY be used with Servo Bias Inputs: ...............................................................................................................12
Microphone RF Bypassing ..................................................................................................................................................................13
Line Level Signals ...............................................................................................................................................................................13
Wiring Diagram for MI33A Instrument Cable ......................................................................................................................................13
Specifications and Features ................................................................................................................................................................15
Troubleshooting ....................................................................................................................................................................................16
Service and Repair ...............................................................................................................................................................................17
Returning Units for Repair ..................................................................................................................................................................17
Rio Rancho, NM
3
LMa
Introduction
The design of the LMa transmitter introduces the advanced technology and features of Digital Hybrid Wireless® in a Lectrosonics belt-pack transmitter at a modest
cost. Digital Hybrid Wireless® combines a 24-bit digital
audio chain with an analog FM radio link to eliminate a
compandor and its artifacts, yet preserve the extended
operating range and noise rejection of the finest analog wireless systems. DSP “compatibility modes” allow
the LMa to be used with a variety of analog receivers
in addition to its native hybrid mode by emulating the
compandors found in Lectrosonics 100 Series, 200
Series and IFB transmitters, and certain receivers from
other manufacturers (contact the factory for details).
Changing the compatibility mode is accomplished with
a simple procedure using the frequency switches and
power switch.
The housing is a rugged, machined aluminum package
with removable, stainless steel wire belt clip. The input
jack is a standard Lectrosonics 5-pin type for use with
electret lavaliere mics, dynamic mics, musical instrument pickups and line level signals. The LEDs on the
front panel allow quick and accurate level settings without having to view the receiver. The battery compartment accepts any 9 volt battery and makes a positive
connection via self-adjusting contacts. The antenna is
a super-rugged, permanently attached 1/4 wavelength
design made of flexible galvanized steel cable.
The switching power supplies in the LMa provide
constant voltages to the transmitter circuits from the
beginning (9.3 VDC) to the end (5.5 VDC) of battery life,
with output power remaining constant over the life of the
battery. The input amplifier uses an ultra low noise op
amp for quiet operation. Input gain is adjustable over a
43 dB range, with a DSP controlled dual envelope input
limiter to cleanly handle signal peaks over 30 dB above
full modulation.
Digital Hybrid Technology
All wireless links suffer from channel noise to some
degree, and all wireless microphone systems seek to
minimize the impact of that noise on the desired signal.
Conventional analog systems use compandors for
enhanced dynamic range, at the cost of subtle artifacts
(known as “pumping” and “breathing”). Wholly digital
systems defeat the noise by sending the audio information in digital form, at the cost of some combination of
power, bandwidth, operating range and resistance to
interference.
The Lectrosonics Digital Hybrid Wireless® system overcomes channel noise in a dramatically new way, digitally
encoding the audio in the transmitter and decoding it
in the receiver, yet still sending the encoded information via an analog FM wireless link. This proprietary
algorithm is not a digital implementation of an analog
compandor but a technique which can be accomplished
only in the digital domain.
Since the RF link between transmitter and receiver
is FM, channel noise will increase gradually with
increased operating range and weak signal conditions, however, the hybrid system handles this situation elegantly with rarely audible audio artifacts as the
receiver approaches its squelch threshold. In contrast,
a purely digital system tends to drop the audio suddenly
during brief dropouts and weak signal conditions. The
Digital Hybrid Wireless® system simply encodes the
signal to use a noisy channel as efficiently and robustly
as possible, yielding audio performance that rivals that
of purely digital systems, without the power, noise and
bandwidth problems inherent in digital transmission.
Because it uses an analog FM link, Digital Hybrid Wireless® enjoys all the benefits of conventional FM wireless
systems, such as excellent range, efficient use of RF
spectrum, and long battery life.
Frequency Agility
The transmitter section uses a synthesized, frequency
selectable main oscillator. The frequency is extremely
stable over a wide temperature range and over time.
Two rotary switches, located on the side panel provide
256 frequencies in 100 kHz steps over a 25.6 MHz
bandwidth.
Wide-Band Deviation
In the Digital Hybrid and 200 Series modes, the system uses ±75 kHz deviation to dramatically improve
the capture ratio, and signal to noise ratio of the overall
wireless system.
Long Battery Life
The use of switching power supplies throughout the
design allows over 6 hours of operation using a single 9
volt alkaline battery and over 7 hours of operation with
a 9 volt LiPolymer rechargeable battery. The battery
contacts are spring loaded to prevent “rattle” as the unit
is handled.
Servo Bias Input and Wiring
The LMa input preamp is a radically different design than
previous Lectrosonics transmitter inputs. The improvements are audible and make the transmitters easier to
use and much harder to overload. It is no longer necessary on some mics to introduce pads to prevent overload of the input stage, divide the bias voltage down for
some low voltage mics, or reduce the limiter range at
minimum gain settings.
Two different microphone wiring schemes are now
available to simplify and standardize the configuration.
Simplified 2-wire and 3-wire configurations for the servo
bias input only take full advantage of the preamp circuitry to maximize the signal to noise ratio, and several
other configurations are available that are compatible
with the servo bias input and earlier types.
The input will automatically switch the low frequency
roll-off to 35 Hz when the MI33ARA and MI33AST
instrument cables are connected.
4
LECTROSONICS, INC.
Input Limiter
The transmitter employs a digitally-controlled analog
audio limiter prior to the analog-to-digital converter.
The limiter has a range greater than 30 dB for excellent
overload protection. A dual release envelope makes the
limiter acoustically transparent while maintaining low
distortion. It can be thought of as two limiters in series,
connected as a fast attack and release limiter followed
by a slow attack and release limiter. The limiter recovers
quickly from brief transients, so that its action is hidden
from the listener, but recovers slowly from sustained
high levels to keep audio distortion low and preserve
short term dynamic changes in the audio.
No Pre-Emphasis/De-Emphasis
Because the signal to noise ratio of the hybrid system is
so high, there is no need for conventional pre-emphasis
(HF boost) in the transmitter and de-emphasis (HF roll
off) in the receiver. Thus, the possible distortion problems associated with pre-emphasis and de-emphasis
are eliminated.
Pilot Tone Squelch
The DSP in the transmitter generates one of 256 different ultrasonic tones between 25 and 32 kHz to operate
the receiver squelch (audio muting). The benefit of a
pilot tone squelch system is that the receiver will remain
quiet until it receives the pilot tone from the matching
transmitter, even if a strong RF signal is present on
the carrier frequency of the system. The pilot tone also
eliminates noise (pops, thumps, etc.) from occurring
when the transmitter is powered on and off.
Frequency-Agile UHF Belt-Pack Transmitter
The pilot tone frequency is chosen according to which
of the 256 channels has been selected by the frequency switch setting. This ensures that all transmitters in
a system have different pilot tone frequencies so even
spurious RF from the wrong transmitters can’t open the
receiver squelch.
Circulator/Isolator
The transmitter RF output circuit includes a specialized
RF device called a “circulator/isolator” or simply “isolator.” The device uses a magnetically polarized ferrite to
allow RF signals to pass through to the antenna, but it
blocks them from coming back into the output amplifier.
This greatly reduces RF intermodulation produced in
the transmitter output stages when multiple units are
used in close proximity (a few feet apart). The isolator
also helps protect the output stage from electrostatic
shock delivered to the antenna. Isolators are common
in broadcast and commercial applications, but because
of their high cost it is unusual to find them in wireless
microphone systems.
LMa Block Diagram
Bicolor
Modulation
LEDs
+5v
Freq
Switches
9V
Battery
Bicolor
Power
LED
Rio Rancho, NM
5
LMa
Controls and Functions
Input Jack
The 5-pin (Switchcraft TA5F compatible) input accommodates virtually every lavaliere, hand-held or shotgun
microphone available, and most musical instrument
signals. Line level signals can also be accommodated.
(See 5-Pin Input Jack Wiring.)
Power ON/OFF Switch
The Power ON/OFF switch turns the transmitter on and
off. The pilot tone muting system prevents transient
noise (pops, thumps, etc.) from occurring at the receiver
even if the transmitter is abruptly switched on or off.
Power LED
The Power LED glows green when the transmitter is
operating and the battery is good. It turns red when the
battery voltage drops to 6.1 VDC and starts blinking
red when the voltage drops to 5.6 VDC. When using a
recommended lithium or alkaline battery, there will be
about 30 minutes of operating time remaining when the
Power LED first begins blinking red.
AUDIO LEVEL
control
Power LED
Antenna
Battery Compartment Door
Input Jack
Modulation
LEDs
Power
ON/OFF
Note: A weak battery will sometimes cause
the Power LED to glow green, but it will soon
discharge to the point where it will turn red or go
out completely. If in doubt, replace the battery with
a known new battery. If the Power LED fails to
glow when the transmitter is turned on, replace the
battery.
LiPolymer rechargeable batteries give little or no warning when they are depleted. If you wish to use these
batteries in the transmitter, you will need to manually
keep track of the operating time to prevent interruptions
caused by dead batteries. Start with a fully charged battery, then measure the time it takes for the Power LED
to go out completely.
Note: A number of Lectrosonics receivers
incorporate a Battery Timer function which tracks
the amount of time the transmitter signal is
detected. See your receiver manual to determine if
this function is available and, if so, the instructions
on measuring the actual run time of the battery.
Frequency Select Switches
Two 16-position rotary Frequency Select Switches, accessed through the left side panel, are used to adjust
the transmitter’s operating frequency. These switches
are labeled 1.6M and 100K. The 1.6M switch is used for
coarse frequency adjustments and the 100K is used for
fine frequency adjustment.
Modulation LEDs
The Modulation LEDs provide a visual indication of the
input audio signal level from the microphone or musical
instrument. These two bicolor LEDs can glow either red
or green to indicate modulation levels.
Frequency Select
Switches
The Modulation LEDs are also used to indicate the
Compatibility Mode when the transmitter is initially
turned on. The Modulation LEDs will blink simultaneously:
• Oncefor100Seriesmode
•Twotimesfor200Seriesmode
•Threetimesformode3
•FourtimesforDigitalHybrid(400Series)mode
•FivetimesforIFBmode
•Sixtimesformode6
Belt Clip
Attachment Holes
Audio Level
The AUDIO LEVEL control is used to set the input gain
for the proper modulation.
Antenna
The flexible, insulated galvanized steel cable antenna
supplied with the transmitter is cut to 1/4 wavelength of
the center of the frequency block (the frequency range)
of the transmitter.
Belt Clip
The belt clip may be removed for special applications
by pulling the ends out of the holes in the sides of the
case. An optional hinged belt clip (P/N BCHINGED) is
also available. Contact a Lectrosonics sales representative, or visit our web site (www.lectrosonics.com) for
more details.
6
LECTROSONICS, INC.
Loading...