Lectrosonics LCA16 User Manual download pdf (Page 3)

GENERAL TECHNICAL DESCRIPTION

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

Figure 1 - LCA16 Block Diagram

"A"

ATTENUATION

"B"

ATTENUATION

"B"

ATTENUATION

"A"

ATTENUATION

PWR

AMP

SPKR +

SPKR -

16 16

16 LINES

16 LINES 16 LINES

TO CHANNELS 2 THROUGH 16

MAIN LEVEL

L O G IC S IG N A L CO N D IT IO NIN G L O G IC S IG N A L CO NDIT IO N IN G

LINE OUT -

LINE OUT +

GROUND

BALANCED

LINE DRIVER

ATTENUATION

SELECT LOGIC

AND

LED DRIVERS

"A"

ATTENUATION

"B"

SELECT SWITCHES

ATTENUATION

SELECT SWITCHES

FRONT

PANEL

LEDs

CH. 1

TO CHANNELS 2 THROUGH 16

AUDIO

BALANCED

INPUT

AUDIO

THROUGH

OUTPUT

INPUT

AMPLIFIER

SIGNAL

PRESENT

1 2 3 4 5 6 7 8 ... 17 18

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