Lectrosonics CR185 User Manual

CR185

COMPACT RECEIVER

OPERATING INSTRUCTIONS

and trouble-shooting guide

LECTROSONICS, INC.

Rio Rancho, NM

INTRODUCTION

Thank you for selecting the Lectrosonics Professional Series wireless microphone system. This system
represents well over 10 years of manufacturing experience in wireless microphones, and almost 70
years of design experience.

The CR185 receiver design is the result of surveying the needs of professional video producers, ENG
cameramen and many others in the broadcast and pro video industry. Hundreds of conversations with
dealers and end-users developed the final parameters for the design.

The CR185 receiver is a fixed frequency design that eliminates the need to "tune" or adjust the receiver
every time it is used. This is the preferred design for a number of reasons, among them simplicity of
operation, no adjustments in "high pressure" situations, and interference rejection by design rather than
by trying to "tune" it out.

The CR185 miniature receiver was designed by professionals for outstanding performance and
flexibility, while preserving ease of operation. It is compatible with all Lectrosonics high band
transmitters. The CR185 receiver represents one of the best values in wireless receivers, regardless of
price.

TABLE OF CONTENTS

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

GENERAL TECHNICAL DESCRIPTION .......................... 2

CONTROLS AND FUNCTIONS

FRONT PANEL ..................................... 3

REAR PANEL ...................................... 5

BATTERY REPLACEMENT ................................... 5

ANTENNA USE AND PLACEMENT ............................. 6

OPERATING INSTRUCTIONS ................................. 7

INDICATOR QUICK REFERENCE .............................. 7

TROUBLESHOOTING ....................................... 8

CR185 REPLACEMENT PARTS AND ACCESSORIES ............... 8

SERVICE AND REPAIR ..................................... 9

RETURNING UNITS FOR REPAIR ............................. 9

SPECIFICATIONS AND FEATURES

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

............................ 10

1

GENERAL TECHNICAL DESCRIPTION

JFET

RF AMP

ANT

LC FILTERS

2:1

SQUELCH

NOISE

AUDIO

0.5uV

2 SECTION

HELICAL

RESONATOR

2 SECTION

HELICAL

RESONATOR

JFET

RF AMP

2 SECTION

HELICAL

RESONATOR

1ST

LOCAL

OSCILLATOR

DBL BAL

DIODE
MIXER

1ST

IF AMP

6 POLE

HIGH FREQ

CRYSTAL

FILTER

DBL BAL

ACTIVE MIXER

2ND

LOCAL

OSCILLATOR

2ND

IF AMP

ACTIVE FILTERS SEPARATE

NOISE AND AUDIO

DBL TUNED

DISCRIMINATOR

COMPLEMENTARY

EXPANDER

BALANCED

OUTPUT STAGE

HEADPHONE

AMP

The CR185 receiver is comprised of six major functional subsystems: the RF front-end amplifier, the
double balanced mixer/local oscillator, the first IF filter, the second IF filter and audio demodulator, the
compandor, and the balanced microphone level output circuit.

The RF front-end amplifier consists of three cascaded pairs of helical resonators for high selectivity.
Between the first and second helical resonators, and the second and third helical resonators are low
noise grounded gate JFET amplifiers. These amplifiers are designed to provide only enough gain to
make up for the loss through the helical resonators. This combination of low front-end gain, coupled
with the extremely high selectivity of the cascaded helical resonators results in no overloading, even on
extremely strong signals. Rejection of out of band signals is maximized, and intermodulation products
are suppressed.

The mixer stage consists of a high level double balanced diode mixer. The oscillator is biased from a
/regulated supply, yielding stable performance over the entire life of the battery. The local oscillator
crystal operates at approximately 16mHz, and can be adjusted above and below the nominal frequency
in order to place the 21.4mHz IF in the center of the crystal filter’s narrow passband. The high
selectivity of the crystal filter stage further minimizes the possibility of interference from signals on
adjacent frequencies.

The second IF filter and the audio demodulator, as well as the squelch and RF output LED drive are
provided by one monolithic integrated circuit. The second IF filter is centered on 1mHz, and drives a
double tuned quadrature type FM demodulator. The squelch circuit is a supersonic noise detector type
and is factory set for a -20dB SINAD level (about .5uV). The squelch level is regulated and
temperature compensated to maintain a consistent squelch level under all conditions.
The compandor is driven by a multiple pole active low-pass filter. The filter ensures that supersonic
noise will not cause the compandor to increase gain incorrectly. This filter also drives the -20dB
modulation LED. The compandor senses the signal level, and dynamically increases the gain for loud
signals or decreases the gain for soft signals. In this way, the original dynamic range of the transmitted
signal is restored, while preserving a high signal-to-noise ratio. The expansion ratio is 2:1, which
produces a 2dB change in output signal level for a 1dB change in input level. In addition, the
compandor has a de-emphasis network that is complementary to the pre-emphasis network in the
transmitter.

The balanced microphone level output circuit generates a truly balanced signal at the XLR output
connector. The volume control is a balanced attenuator, and gives a gain range from -20dBV (at full
modulation) in the fully clockwise position to -50dBV in the fully counter-clockwise position. In addition,
the headphone circuit is driven from the microphone circuit. This means that the headphone output
level is dependent not only on the headphone volume control, but also the microphone level control.

Figure 1 - CR185 Receiver Block Diagram

2

CONTROLS AND FUNCTIONS

RECEIVER FRONT PANEL

MODULATION LEDs

Indicate the modulation (audio level) of the incoming signal, and can be used for proper adjustment of
the transmitter’s "MIC LEVEL" or "GAIN". The -20 LED glows when the transmitter modulation is at a
high enough level to produce a good audio signal-to-noise ratio. It will normally flicker, or stay lit as
you speak into the microphone. The 0dB lamp indicates a "peak," showing that the transmitter
modulation is at maximum. Constant lighting may indicate that the audio gain in the transmitter may be
set too high. It is normal and desirable that you see an occasional flicker of the 0dB lamp in typical
use.

OUTPUT CONTROL

Attenuates the audio output level of the receiver to match the input requirements of the equipment with
which it is used. The XLR output jack on the rear panel provides an audio output at microphone level
for low impedance, balanced inputs. At the extreme counter-clockwise position of the control knob, the
output level of this XLR jack will be 50dB at full modulation. In the fully clockwise position, the output
level will be -20dB at full modulation. Intermediate settings are sometimes necessary due to the
variations in different input compressors and ALC (automatic level control) circuits on various VCR’s
and audio inputs. The markings around the control knob are provided simply as "memory markers;"
they are not calibrated with reference to a specific output level.

EXT/OFF/INT SWITCH

Turns the receiver power off and on and selects either internal 9 Volt battery power, or external 12 Volt
DC power (of either polarity).

POWER LED

Glows when the power switch is in the proper position and the battery is good, or when external 12 Volt
DC power is properly supplied. If this LED is very dim or does not light up when the switch is turned
on, replace the battery or check the connections from the external power source. The LED glows
brightly to indicate a good battery and dims as the battery voltage decreases.

The POWER LED is connected to a precision battery test circuit that continuously monitors battery
voltage. The LED is at full brightness with a new 9 volt alkaline battery. As the battery voltage drops
during use, the LED brightness will also decrease. After 4 to 5 hours, the battery voltage will be about
7 volts. The LED will be completely extinguished.

IMPORTANT!

When the battery voltage drops below 6 Volts, the power LED will remain off, but the other 3

LEDs will light up and a loud rush of audio noise will be heard as the squelch opens. This

condition is normal, and is easily remedied by replacing the battery.

3