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INSTALLATION
PRECAUTIONS
The A-27 weighs a full 26kg and so be sure to
install
it in a location
which
can
support
heavy
weights.
Also, take care
when
trans-
porting the A-27 from one place to another
and when otherwise handling it.
Don't put anything on the top of the A-27
because a high-power amplifier will produce a
lot of heat. Also leave sufficient space around
the amplifier for adequate ventilation.
CONTENTS
FOAtures
cacue sea
tw
aaa eae ear ea
ES
2
Stereo System Composition
...........
4
Installation Cautions
..............-.
4
Connection Diagram ..............206-
9)
CONNECTIONS:
5d. aie
Sas
FG
ew
6
Front Panel Facilities ........
Welk Gaede
8
Operations
4.4. c-ice een
6 eee &
10
Effective Operations .................
11
Using the Tape Decks ................
13
Using the PRE OUT,
POWER AMP IN jacks .............
14
Conditions Frequently Mistaken
for Malfunction
................4..
16
SpeCileatlons cvs
ee
ence aaa
Insertion
Characteristics Charts ...........
Insertion
Schematic Diagram.............
Insertion
FEATURES
Power Amplifier with a Magni-wide Power Range,
Low Distortion and Continuous Power Output of
120W Per Channel
The A-27 stereo amplifier incorporates a current mirror
load cascade connected to a single-stage differential ampli-
fier with dual transistors, a Class AB triple-stage Darlington
circuit, a parallel
push-pull
circuit and a pure comple-
mentary OCL circuit.
Pioneer's newly developed Ring Emitter Transistors (RETs)
with excellent high-frequency-range characteristics at high-
output power ratings are adopted for the Class AB power
stage. These help the amplifier display an ultra-wide power
range and deliver a
Continuous Power Output of 120 watts" per chan-
nel, min., at 8ohms
from 5 Hertz to 30,000
Hertz with no more than 0.012% total harmonic
distortion.
The power amplifier is configured as a DC power amplifier
with
the capacitors
removed from the NFB
circuit for a
superbly low distortion all the way from very faint outputs
up to full power.
In the output range which is actually used (3W/8 ohms),
the power amplifier works as a Class
A model, enabling
you to enjoy music delivered by a Class A amplifier with
magnificient linearity.
Independent
Left and Right Power Supplies that
Back Up the High and Stable Power Output
The large-sized transformers with their superb regulation
packing quite a punch, and the large-capacity (18,000uF)
electrolytic capacitors (two per channel) are featured in the
independently positioned dual power supply circuits with
separate power transformer windings to provide power for
the left and right channels. These power supplies not only
deliver a stable output of power at all times but they also
help give low-frequency-range sound reproduction with an
unusually singular regulation and damping even during high
outputs.
The primaries of the power transformers contain inrush-
current
suppressors
which
serve
to suppress
high-value
inrush currents when
the power
switch
is thrown
to ON.
These circuits reduce the load on each of the parts that
make up the dynamic power supplies, and also successfully
enhance the degree of reliability.
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