Accuphase C 280 V Brochure

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C-280V

PRECISION STEREO PREAMPLIFIER

O High-Quality, Balanced Transmission Line Ampiifier 0 Class A Pushr
Puil Amplifier with DC Servo System for Ail Stages 0 Independent Four
Power Supplies for Len and Right Amplifier and Equaiizer Circurts 0 Con»
dUCliVe PIBSNC Audio Volume with Four Synchronized Variabie Elements

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Accuphase's reputable preamplifier 0-280 was
introduced to the market in December f 982, and
about the same time the first CD players were
produced. To exhibit the merits of CDs, the O
280 incorporated an innovative, cascode-type
classA(all-stage) push-pull amplifiercircuit and
an analog equalizer. The 0-280, which was re-
garded as the worlds highest grade amplifier,
incorporated the balanced power transmission
system conforming to Accuphase's quality con
trol.

In 1987, the C-280L. an improved version of
the C-280 series amplifiers, incorporated a bat-
anced circuit composed of two amplifiers. The
C-280L made it possible to receive signals from
CD players. power amplifiers, and other audio
equipment to the C-280L Via balanced cables
The highly sophisticated C-280L was then con-
sidered the king of preamplifiers,

Now, the Cv280V, the most perfect pream-
plifier yet produced, has made its debut. It was
developed based on Accuphases established
techniques with the concept that preamplifiers
should correspond to various program sources
and have a perfect signal transmission circuit.

All the ctrcuits ofthe C-280V have been newly
developed. The most outstanding characteristic
of the Cv280V is that only one circuit is needed to
transmit both balanced and unbalanced signals
without passing through any additional circuits.
which can cause deterioration of sound quality,
The C-28OV, which has an ideal amplifier ctrcuit.
incorporates an analog equalizer with an input
circuit exclusively used for Signals from MM or
MC cartridges.

The power supply circuit of a preamplifier is as
important as that for the power amplifier and has
a great influence on audio quality Because a
high capacity is demanded from the power sup-
ply circuit, the C-280Vs amplifiers and equaliz-
ers (both left and right) are equipped with inde-
pendent power supplies.

To further improve the audio quality. the C-
280V incorporates tour power supplies. each
with an independent transformer.

The volume control, which was exclusively
developed for the C-28OV, uses an innovative.
newly developed conductive plastic resistor. in-
stead of the collectors rotating. the resistor ele-
ments rotate, thus reducing a great deal of the

High-Quality Balanced Transmission
Line Amplifier with Class A Push-Pull Circuitry.

Each Amplifier Unit with

CP (Conductive Plastic) Audio Volume,
Supported by Independent Four Power Supplies.

metal contact area, This has made it possible to
eliminate sound deterioration to almost nil.

Each amplifier unit is secured with a thick
aluminum housing and mounted on an 8-mm-
thick rigid aluminum frame. This insulates each
amplifier unit and effectively cuts mechanical
vibration.

Accuphase's high quality C-280V incor»
porates gold plated printed crrcuit boards as
well as finest quality copper wire,

High-Quality, Balanced Transmission Line
Amplifier

The line amplifier can be compared with a city's
main street since all sources must pass through
the line amplifier. Accuphase has incorporated
a balanced transmission circuit which has
symmetrical signals paths. each for plus and
minus signals, the phases of which are opposite
each other and are transmitted simultaneously,
This system eliminates noise effectively, which is
why it has been adapted by broadcasting sta-
tions and audio professionals,

Recently, a high frequency noise has in
creased with the use of ever increasing numbers
of home electronics equipment. Such noise in-
trudes through power lines or signal cables and
reduces audio quality. The balanced transmis-
sion system cuts out such noise effectively.

The line amplifier of the C-280V is a high
quality balanced transmission line amplifier (re-
fer to Fig. 2). The circuit (a) works as a balanced
transmission line amplifier, while circuit (b)
works as an unbalanced transmission line am-
plifier. The C-280V incorporates three differenti-
al amplifier units. AMPt is for input use and
AMP2 and AMP3 are for output use. In balanced
transmisston. Signals can be input from both the
plus and minus terminals of AMPt, The signals
are then amplified and output to AMP2 and
AMP3. AMP2 feeds back its output to AMP3
while AMP3 feeds back its output to AMP2. Both
AMP2 and AMPS work together. producing
symmetrical low impedance stgnals. In this cirs
cuit. even if either one of the output lines is
grounded. normal output signals can be ob-
tained. Therefore, in unbalanced transmission.
each one of the input lines and the output lines
can be grounded to obtain unbalanced output
signals, Since only one circuit is used for bal-

anced and unbalanced transmission. there is no
difference in audio characteristics between bal-
anced and unbalanced transmission. and there-
fore an ideal amplification is achieved.

Class A (All-Stage) Push-Pull Amplifier
with Dc Servo System

Fig. 3 is the circuit diagram of the C-280V's line
amplifier. All the amplifier units incorporate
Accuphase's original symmetrical push-pull cire
cuits. Since electrical stability is demanded for
the input circuits, all the input circuits are the
cascade source follower type. thus achievtng
stable operation in a wide frequency range from
the low frequency to the ultra-high frequency.
The output stage employs a complementary

darlington push»pull circuit. keeping loyn'ntput, »r

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impedance and excellent linearity in a wr
put range.

These amplifier units are DC amplifiers. In DC
amplifiers. even minute direct current in the out-
put srgnals can cause noise. The C-280V incor-
porates an effective DC servo circuit which pre-
vents any DC drift.

independent Power Supplies lor Left and
Right Amplifiers and Equalizers

The C-280V incorporates four independent
power supplies (the total capacitance of the
filters is 120.000uF) for best analog reproduc-
tion.

All the amplifier units are equipped with
broad-range constantvoltage power supplies,
thus preventing interference between the am-
plifiers.

Accuphases Exclusive Conductive Plastic
Audio Volume

An amplifier needs a good audio volume control,
The C-ZBOV uses a new innovative conductive
plastic (CP) type volume control similar to that
used in sophisticated recording studios. A CP
resistor is a variable resistor with little "" ct
reststance. thus ensuring low audio disto . it
is processed at high temperature after a resistor
element is printed on it and has gold-plated
brush contacts.

Each external terminal is combined into a
single unit made of only one metal type thus
reducing distortion. Note that the brush of the CP

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Fig. 1 Block diagram at C-ZBOV (one channel)

fig. 2 Principle at the balanced/unbalanced

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transmission