Fisher CA 4500 Service Manual

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SERVICE MANUAL

IFISHER
CA- 4500

Stereo Pre-Amplifier
(EUROPE)

T he first name in high fidelity

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INTRODUCTION

A-C LASS PUSH-PU LL EOUALIZER

Bare characteristic is prominently improved and, high stability
and ability are obtained by adopting A-class push-pull circuit
(two-step differential amplifier, current mirror turn-over

system).

EOUALIZER

Two-way power (i75V) is supplied to the unit and 40 dB gain
is obtained at 1 kHz. However, the unit maintains allowable
input voltage of 500 mV (distortion factor: less than 0.1% at
1 kHz). RIAA correcting circuit uses NiCr vaporized resistance
of ultra-accuracy (i5%) and a styrol condenser.

The deviation is within 30 - 15 kHziO.1 dB.

TONE CONTROL AMPLIFIER

Since the output step (differential input and :2 power system)
uses SEPP circuit system, adequate output voltage can be
obtained without distortion. Moreover, Signal to Noise Ratio

is improved and dynamic range is widened.

TURN-OVER SWITCH

TWo-step or separative (right and left) switching is possible.
Discrete element and 11-contact rotary switch are jointly used
for fine-adjustment of bass and treble. Therefore, 2 dB step
adjustment will be correctly performed.

LOUDNESS CONTROL

Continuance system by discrete element is used for the unit.
Natural controlling can be performed with 4 dB step.

AUDIO MUTING

The unit takes the system in which the muting circuit bypasses
the tone amplifier with 20 dB gain.

When the filter circuit is switched off, the signal through the
function switch is directly produced in the output terminals.
Therefore, it is possible to directly drive the main amplifier
with this muting switch as the gain in the equalizer circuit is
approximately 40 dB.

A-CLASS MONITOR AMPLIFIER

Power amplifier equipped with push-pull OCL circuit of
differential input A-class (output 1W) is built in the unit.
If an efficient speaker is connected with the unit, adequate
volume will be obtained. It is also very convenient for
checking the program source or monitoring the concert.

POWER SOURCE MUTING 81 CONSTANT-VOLTAGE
POWER SOURCE

The unit is set in normal function mode as soon as the switch
is turned on because of two-way power system, differential
input and SEPP output circuit.

However, the unit is set not to produce signals in the output
terminals for about 4 seconds.

An abnormal signal will not be produced in the power amplifier
and excessive input will not be applied to the speakers at all.
The power source, in which all amplifying steps except monitor
amplifier output step are perfectly stabilized, is supplied to the
unit. Therefore, the unit functions effectively in a stabilized
mode whenever any kinds of signals are produced.