Lafayette LR 1500T Owners Manual Schematic

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A Lafayette First!

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COMPUTOR-MATIC®

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lVIodel LR-15OOT

Stock No.99-0190WX

Installation And Operating Manual

l75-VVatt Solid State £1!
ADI/Flu Stereo Receiver "3 J
With 1

COMPUTO R- MATIC @ V 5 1; :5
Overload Protection 3 "
Featuring I
Four Integrated Circuits
Two Field Effect Transistors 15-:

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Model LR-1500T
I75-Watt Solid State
AM/FM Stereo Receiver

FEATURING

New Revolutionary Integrated Circuits

MTEGRATED Electronic Miracle
I:IRCUIT
Inn. of the Space Age
Revolutionary new electronic devices that are the ultimate in miniaturi-
zation and reliability. Each no larger than a tiny transistor, yet housing a
complete circuit with many transistors. diodes and resistors. Provides

improved performance in far less space-assures reliability for years to
come.

Advanced COMPUTOR-MATIC Over-Load
Protection Circuit [Patent Pending).

A new fuseless computer-type overload protection circuit (Pat. Pend.)
that automatically guards against damage to drivers and output transis-
tors. Not only is this protective circuit hundreds of times faster than a
fuse, but it is also self-restoring. When the cause of overload is removed,
the circuit automatically restabilizes. allowing resumption of normal
operation.

Silicon Field Eifect Transistors

Two high-performance silicon Field Effect Transistors [FETs] in FM
front-end" assure high overload capability, superior cross-modulation
index and image rejection.

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AUTOMATIC

OVERLOAD PROTECTION CIRCUIT

This receiver is equipped with COMPUTOR-MATIC--a newly-
developed overload protection circuit (patent pending) that eliminates
any possibility of damage to drivers and output transistors caused by
momentary or sustained overloads. A special 2-transistor circuit is used
in each channel that continuously monitors the output transistor
stages. Any abnormal condition is immediately sensed and the protec-
tive circuit will act instantly to out off operation of the amplifier before
damage can result. Not only is this computer-type protective circuit
hundreds of times faster than a fuse, but it is also self-restoring. When
the cause of overload is no longer present, the circuit automatically be-
gins to restabilize and normal operation is generally resumed within
1 or 2 seconds.

WHY SPECIAL OVERLOAD PROTECTION IS NECESSARY

It is well known that the output transistors in a solid state ampli-
fier can be overloaded and damaged if a short-circuit is placed across
the speaker output. Most units do therefore include a fuse or circuit
that offers suitable protection against this type of overload. However,
the superior transient response and the wider power bandwidth of
todays solid state amplifiers have created another problem. An input
signal of very short duration (caused by lightning or switching, for
example) is faithfully reproduced through the various amplifier stages
in a receiver and appears at the output as a momentary signal of
dangerously high power. This frequently results in output transistor
overload and subsequent damage. The greater the fidelity of the ampli-
fier, the more serious this problem becomes. It is for this reason that a
new and more complex type of circuit has been devised and included in
your receiver.

HOW TO RECOGNIZE THE OPERATION OF THE
PROTECTIVE CIRCUIT IN YOUR RECEIVER.
If an overload occurs (even momentarily) the protective circuit will
operate instantly and the receiver will be silenced. If the overload has
occurred only on one channel, only that channel will be silenced. So

long as the overload exists, the receiver will remain silent on one or
both channels. As soon as the cause of overload is removed, the circuits
will begin to restabilize and, after 1 or 2 seconds, the receiver will
resume normal operation.

On rare occasions, the receiver may not recover from a severe over-
load and remain silent even when the cause has been removed. If this
occurs, simply set the volume control fully counter-clockwise to mini-
mum for 2 or 3 seconds, then return it to its normal position. This
action will speed the restabilization of the circuits.

CAUSES OF OVERLOAD
Overloads can be brought about by a number of causes, either
momentary or permanent.

Momentary overloads can result from severe noise pulses such as
those caused by lightning.r and static, switching noises, or from momen-
tary shorting of speaker lines. Under these conditions, the receiver will
usually resume normal operation within 1 or 2 seconds. Permanent
overloads will result if speaker lines are permanently shorted or if a
sustained signal of abnormally high level is applied to the input of
the amplifier section (such as excessive hum, for example). Permanent
causes of overload must be located and rectified before the receiver
can resume normal operation.

NOTE: Momentary overload can also occur when tuning very rapidly
across the receiver dial with the volume control in a high volume posi-
tion. The sudden pulses of sound produced as the receiver tunes across
the stations appear as large power pulses at the output, sufficiently
high in some cases to cause a momentary overload. Tuning should
therefore be carried out at a slower rate or with volume at a relatively
low level (normal listening).