General Technical Description - Lectrosonics LCA16 Operating Instructions Manual

In the following illustration is a simplified block diagram of the LCA16 showing one amplifier channel. All channels
are identical.
The audio input of the LCA16 is an RF filtered, electronically balanced differential amplifier. An AUDIO THRU
output is provided so the audio signal can be "daisy chained" to other devices if required. A SIGNAL PRESENT
LED on the front panel indicates the presence of signal above -20dBv. The audio signal passes through the MAIN
LEVEL control before being distributed to the output channel amplifiers. Each output channel employs a dedicated
power amplifier. The amplifiers are fully protected from short circuits, thermal overloads or highly reactive loads.
Each amplifier is individually fused, so in the event of catastrophic failure of any single channel, no other channels
will be affected. Each output channel also includes a balanced line level output which is simultaneously available to
drive external amplifiers, or other audio equipment.
The logic input signal conditioning circuits are specially designed to accept a wide variety of logic signals, ranging
from relay contact closures to TTL logic levels. Each logic input passes through a time constant circuit with
hysteresis. This guarantees minimum "signal chopping" caused by changing attenuation during pauses in speech.
Photo-conductive opto-isolators are employed to switch the level of attenuation of the audio. These devices
eliminate the abrupt audible changes that occur when hard switching is used.
DIFFERENTIAL
AUDIO
INPUT
THROUGH
AMPLIFIER
OUTPUT
AUDIO
BALANCED
INPUT
L
O
G
I
C
I
N
P
U
T
S

GENERAL TECHNICAL DESCRIPTION

SIGNAL
PRESENT
MAIN LEVEL
"A"
ATTENUATION ATTENUATION
SELECT SWITCHES SELECT SWITCHES
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
16 LINES
16 LINES
Figure 1 - LCA16 Block Diagram
NO
ATTENUATION
"A"
ATTENUATION
"B"
ATTENUATION
"B"
ATTENUATION
SELECT LOGIC
AND
LED DRIVERS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
16 LINES
2
TO CHANNELS 2 THROUGH 16
PWR
AMP
BALANCED
LINE DRIVER
FRONT
PANEL
LEDs
NO
ATTENUATION
"A"
ATTENUATION
"B"
ATTENUATION
CH. 1
TO CHANNELS 2 THROUGH 16
SPKR +
SPKR -
LINE OUT -
LINE OUT +
GROUND