Accuphase C 290 V Brochure

Page 2

The C-290V is based on balanced signal trans-
mission technology originally introduced with the
(3-290. It also makes use of the current feedback
principle developed by Accuphase and highly
praised throughout the audio world for its superb
performance and sound quality All circuit aspects
were further refined and broughtto an even higher
level of perfection All circuit parts and compo»
nents were individually selected on the basis of
their sonic properties. The result is an analog
preamplifier that stands at the very pinnacle of
its field,

In its standard configuration, the C-290V is a pure
line-level amplifier, but by installing the optional
phono equalizer unit AD-290V, it allows top-grade
analog disc reproduction as well. The balanced
output stage employs complementary bridged
feedback which allows total isolation from the
ground |ine.The printed circuit boards which play
a very important role in the sound of a preampli-
fier are made from a Teflon material (glass fluo-
rocarbon resin) with low dielectric constant and
low loss. Goldvplating of all signal traces further
improves reliability and signal purity for optimum
sound

The four modules which house the line input and
balanced output circuitry use specially thick alu-
minum with high rigidity. The modules are ar-
ranged on a motherboard firmly mounted to a hard
aluminum chassis for electrical isolation and
mechanical vibration suppression. Complete
dual-mono construction with separate power
transformers and filtering capacitors reliably pre'
vents any unwanted interaction between the two
stereo channels.

The core of the power transformers is made of
an amorphous alloy core with outstanding fre-
quency characteristicsiThe volume control which
is another important aspect is a four-gang type
which uses CP (conductive plastic) resistor ele-
ments for exceptionally clean sound. Hermetically
sealed, logic-controlled relays at strategic loca-

tions make it possible to keep signal paths ex-
tremely short, Every single part and every choice
of material serves one overriding goal: to repro-
duce music with the true splendor of a live perfor-
mance.

Current feedback topology prevents phase
shifts

The amplifying circuits in the C-290V use the
current feedback method for negative feedback.
The operating principle is shown in Figure 2, At
the input point of the feedback loop, the imped-
ance is kept low and current detection is per~
formed. A trans-impedance amplifier then con~
verts the current into a voltage to be used as the
feedback signal, Since the impedance at the cur-
rent feedback point (current adder in Figure 2) is

- input

Current adder
Eulier _ w WP"
converter
" Traits-impedance amplifier

Euller
Curlenl NFB
network

Figure 2 Principle of current feedback amplifier
very low, there is almost no phase shift. Phase
compensation therefore can be kept at a mini«
mum. A minimal amount of NFB results in maxi-
mum improvement of circuit parameters. The re-
sult is excellent transient response and superb
sonic transparency, coupled with utterly natural
energy balance. Figure 3 shows frequency re-
sponse for dif-
ferent gain set-
tings of the cur
rent feedback
amplifier. The
graphs demon-
strate that re-
sponse remains

uniform over a H. H F'Wwlfi " k
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Figure 1 Block circuit diagram of C-ZSOV (one channel)

BALANCED
when:

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UNBALANCED
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A new chapter in analog excellence - The ultimate analog preamplifier with
current feedback design. Teflon-base printed circuit boards assure optimum
performance and reliability. High-quality four-gang volume control uses CP
elements. Fully dual-mono construction with separate amorphous-core power
transformers for left and right channels. Optional phono equalizer unit al-
lows top-quality analog disc reproduction.

Balanced output stage with bridged feedback
In balanced signal transmission, two identical sig-
nals are transmitted simultaneously with inverted
phase and combined at the receiving end, thereby
canceling out common-mode noise and interfer-
ence. This principle is one of the requirements
for truly high-quality sound,

The principle of balanced sound transmission is
shown in Figure 4, The outputs of the two ampli-

Figure 4 Prfnclple of balanced Ilgnll Inn-million (on. channel)

tiers AMPZ and AMPS are connected to form a
cross-feedback loop, which sends the symmetri-
cal (+) and (-) signals with low impedance to the
next stage. The signals are isolated from the
ground line, resulting in an ideal balanced circuit.
Even if one side of the output is grounded, both
amplifiers continue to operate. and the output
voltage does not change.

Discrete llne amplifier designed for sound
quality

The line amplifier is a pure complementary
push-pull circuit. it is built from discrete compo-
nents and employs the superior current feedback
principle. Phase compensation can be kept to a
minimum. resulting in realistic ambiance.

Printed circuit boards made from Teflon ma-
terial (glass fluorocarbon resin) with low di-
electric constant and low loss

The printed circuit boards consist of a glass fluo-
rocarbon resin material which has a stable. low
dielectric constant as well as superior heat resis-
tance and high-frequency characteristics. It is
therefore found mainly in demanding applications
such as SHF band satellite transmissions and
high-precision measuring instruments, Since
printed circuit boards inevitably act to a certain
extent as a dielectric, it is vital to choose a mate-
rial that provides all the required physical proper-
ties while having a low dielectric constant. The
glass fluorocarbon resin fulfills all of these require-
ments. and gold-plated copper traces furthercon-
tribute to sonic purity.

*Teflon is a registered trademark of DuPont USA.

Complete mono construction with separate
amorphous-core transformers for left and
right channels

The power supply of the C-290V employs a
dual-mono approach with separate power trans-
formers and filtering capacitors for the two stereo
channels. Each unit amplifier is equipped with a
wide-range low-impedance voltage regulator to
eliminate possible interference between stages.
The power supply circuitry not only serves as
energy source, but its load current also has con-
siderable bearing on sound quality. The power