Lectrosonics MM400b User Manual
INSTRUCTION MANUAL
MM400B
Watertight Miniature UHF Belt-Pack Transmitter
Featuring Digital Hybrid Wireless™ Technology
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Rio Rancho, NM, USA
www.lectrosonics.com
MM400B
LECTROSONICS, INC. 2
Watertight Miniature UHF Belt-Pack Transmitter
Thank you for selecting the Lectrosonics MM400B
watertight miniature transmitter. The unique design
provides several distinct features for professional
applications:
• Outstanding RF operating range
• Superb audio quality
• Ultra-lightweight, corrosion resistant housing
• Watertight seals for use in wet environments
• Programmable emulation modes for maximum
versatility
The Digital Hybrid Wireless
™
design (US Patent Pending) combines 24-bit digital audio with analog FM
techniques to provide the operating range of the finest
analog wireless systems and the audio quality of a pure
digital system. The 100 mW RF output power extends
operating range, and the DSP controlled, dual-envelope
limiter cleanly handles input peaks to allow higher gain
settings. This combination maximizes operating range
and the signal to noise ratio of the system.
The input provides 6 VDC bias voltage for use with
modern electret lavaliere microphones. Multi-color
LEDs are provided to make input gain adjustments
quick and accurate, without having to view the receiver.
The battery compartment accepts AA alkaline, lithium
or NiMH batteries, and a detachable antenna ¼ wavelength flexible cable connects to a watertight 50 Ohm
SMA port on the transmitter.
The MM400B is machined from a solid aluminum block
to provide the lightweight, rugged package needed in
extreme environments without compromising functionality. Input jacks and controls are O-ring sealed for
watertight protection in wet environments. A special
noncorrosive finish (same as is used on NASA space
vehicles) resists salt water exposure and perspiration in
extreme environments.
The DSP-based design offers backward compatibility
with a handful of earlier analog designs, such as the
Lectrosonics 100 and 200 Series receivers, and other
brands of analog wireless receivers. Compatibility
Modes are easily selected with a sequence of frequency switch settings and cycling the unit’s power.
Only the MM400B transmitter is covered in this manual.
Companion receivers are covered in separate manuals.
Rio Rancho, NM 3
MM400B
LECTROSONICS, INC. 4
Watertight Miniature UHF Belt-Pack Transmitter
Table of Contents
General Technical Description ..............................................................................................................................................................6
General ................................................................................................................................................................................................. 6
Digital Hybrid Wireless™ Technology* ................................................................................................................................................. 6
Low Frequency Roll-Off ........................................................................................................................................................................ 6
Input Limiter .......................................................................................................................................................................................... 7
Digital Signal Processor ....................................................................................................................................................................... 7
Microprocessor, PLL and VCO Circuits ................................................................................................................................................7
Compatibility Modes .............................................................................................................................................................................7
Pilot Tone Squelch ................................................................................................................................................................................7
Wide-Band Deviation ............................................................................................................................................................................ 7
Magnetic Power ON/OFF Switch .......................................................................................................................................................... 7
Battery Life ........................................................................................................................................................................................... 7
Frequency Agility .................................................................................................................................................................................. 7
Circulator/Isolator ................................................................................................................................................................................. 7
Controls and Functions .........................................................................................................................................................................8
Preventing Internal Corrosion ............................................................................................................................................................... 8
Power ON/OFF Switch ......................................................................................................................................................................... 8
Power LED ............................................................................................................................................................................................ 8
Mic Jack................................................................................................................................................................................................9
Audio Level ...........................................................................................................................................................................................9
Modulation LEDs ..................................................................................................................................................................................9
Frequency Select Switches ..................................................................................................................................................................9
Antenna ................................................................................................................................................................................................9
The Belt Clip .......................................................................................................................................................................................10
Battery Installation ..............................................................................................................................................................................10
Operating Instructions ........................................................................................................................................................................11
Selecting the Compatibility Mode .......................................................................................................................................................11
Adjusting Transmitter Frequency ........................................................................................................................................................ 11
Attaching a Microphone and Adjusting Audio Levels ......................................................................................................................... 12
Power Switch Function Selection ....................................................................................................................................................... 13
Determine Power Switch Function Mode ........................................................................................................................................ 13
Changing Power Switch Function ................................................................................................................................................... 13
Replacing the Power Switch Magnet Housing Assembly ................................................................................................................14
Microphone RF Bypassing .................................................................................................................................................................. 15
Replacement Parts and Accessories .................................................................................................................................................16
UHF Transmitter Antenna Specifications ............................................................................................................................................ 16
Troubleshooting ...................................................................................................................................................................................17
Specifications and Features ............................................................................................................................................................... 18
Service and Repair ...............................................................................................................................................................................19
Returning Units for Repair ..................................................................................................................................................................19
Rio Rancho, NM 5
MM400B
General Technical Description
General
The 400 Series (or Digital Hybrid Wireless™) system
uses 75 kHz wide deviation for an extremely high signal
to noise ratio. The switching power supplies provide
constant voltages to the transmitter circuits from the
beginning (1.5 Volts) to the end (0.85 Volts) of battery
life. The input amplifier uses an ultra low noise op amp
for quiet operation. It is gain controlled with a wide
range dual envelope input compressor which cleanly
limits input signal peaks over 30 dB above full modulation.
Note: The terms 400 Series and Digital Hybrid
Wireless™ describe the same product line are
interchangeable.
Digital Hybrid Wireless™ 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 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, even though
the inputs and outputs are analog signals.
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 resistance to interference. However, unlike conventional FM systems, the Digital Hybrid
has done away with the analog compandor and its
artifacts.
Low Frequency Roll-Off
A 12 dB per octave low frequency roll-off is provided in
the audio section, with the -3 dB point at 70 Hz. The
actual roll-off frequency will vary somewhat according
to the low frequency response of the mic capsule being
used.
The low frequency roll-off is used to remove subsonic
(or very low frequency) audio, such as that produced by
air conditioning systems or automobile traffic, from the
audio signal. Excessive low frequency content in the
audio input can cause a variety of audio problems
including driving the transmitter into limiting. For
example, in sound reinforcement systems, as one
instance, excessive low frequency content can cause
excessive power amplifier drain or even damage to
loudspeaker systems.
+6V Bias Supply
(see Input Jack Wiring for details)
Mic
Jack
(Fits Switchcraft
plug #850.)
Hi/Lo
Pass
Filter
Bicolor
Modulation
LEDs
*US Patent Pending
Shunt
Limiter
Phase Locked Loop
4MHz
Reference
Input
Amp
Audio
Level
Freq
Switches
Audio
Microprocessor
A-D
Converter
11001001
Digital Signal Processor
D-A
Converter
11001001
Vol tage
Controlled
Oscillator
Encoded
Audio and
Pilot Tone
Magnetic
Power On/Off
Switch
MM400B
Block Diagram
Switching
Powe r
Supply
1.5V
AA
Lithium
50
Ohm
Isolator
LECTROSONICS, INC. 6
Bicolor
Powe r
LED
+3.3v
+3v
+1.8v
+6v
-3v
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