m Current feedback circuit topology provides outstanding highrange phase characteristics m Six line amplifier units in tripleparallel dual MCS configuration m Fully modular unit amplifierswith discrete circuitry m Tone control circuitry m Option boards
allow digital signal input and analog disc reproduction

Optimum match for P-370 power amplifierThis state-of-the-art
preamplifier features current feedback technology, six fully separate line
amp units in triple-parallel dual MCS configuration, and fully dual-monoconstruction with separate power supplies. Option board allows digital
signal input for top-quality CD reproduction.

Accuphase preamplifiers implement advanced
technology such as current feedback andbalanced signal transmission, in order toachieve optimum quality reproduction that istrue to the spirit of the music. This is the reason
why our products continue to enjoy such a highreputation. The C-245 is a stereo control center
that fully represents Accuphase technologicalexpertise. As the model name indicates, theamplifier stands in the tradition of the C-200/
P300 series that has been the mainstay of
the Accuphase product lineup since its
inception. An ideally matched power amplifier
is found in the model P-370, capable ofdelivering an amazing 400 watts per channel
into an ultra-low-impedance load of 1 ohm.
The line amplifier circuits of the C-245 arebased on the current feedback principle, which
has consistently received high praise for sonicexcellence and top-notch performance. Threeline amplifier modules are used for eachchannel, resulting in a total of six line amp
modules, arranged in a triple parallel MCS(Multiple Circuit Summing) configuration. This
arrangement provides drastic improvements
in S/N ratio, distortion, and other important
performance parameters. All parts used in theC-245 have been carefully selected on thebasis of extended listening tests. Features
such as tone controls and loudness
compensator allow precise fine tuning if
desired, and facilities for tape recorderconnection are also provided. In sound quality
and performance, the C-245 is a superbly
conceived top-notch product.
The possibility of installing option boards
further enhances flexibility. A Digital Input
Board using an MDS (Multiple Delta Sigma)
D/A converter can directly handle the digital
signal from a CD player or similar, for ultrapure music reproduction. A board for faithfulplayback of analog records is also available.

Current feedback circuit topology prevents
high-range phase shifts and ensures
superb sound quality
The C-245 uses the current feedback principle
for negative feedback. Figure 2 shows theoperating principle of this design.
Current adder
Input
Buffer

I-V
converter
Trans-impedance
amplifierAmplifierOutputCurrent NFB
networkFig. 2 Current feedback amplifier principle diagram

Fig. 4 Line amplifier unit circuit diagram(3 units are used in parallel connection per channel)

At the input point of the feedback loop, theimpedance is kept low for current detection.
A trans-impedance amplifier converts the current into a voltage to be used as the feedback
signal. Since the impedance at the current
feedback point (current adder in Figure 2) isvery low, there is almost no phase shift. Phase
compensation therefore can be kept at a minimum. A minimal amount of NFB results inmaximum improvement of circuit parameters.
The result is excellent transient response andsuperb sonic transparency, coupled with utterly naturalenergy balance. Figure
3 shows frequency response fordifferent gain
settings ofthe current Fig. 3 Frequency response with current feedback(Response remains uniform even when gain changes)
feedback amplifier. The graphs demonstrate that response
remains uniform over a wide range.
Fig. 5 Line amplifier (MCS circuit)
operation principle

Six discrete line amplifiers in MCS
configuration designed for optimum soundThe line amp units of the C-245 (Figure 4)

employ a pure complementary push-pullcircuit topology. Hand-selected discrete partsare used in parallel for minimum noise.
Six line amplifiers are connected in a triple
parallel MCS (Multiple Circuit Summing)
configuration developed by Accuphase.
By arranging three line amp units for eachchannel in a parallel connection, theperformance advantages of each circuit
are added up, resulting in improved S/Nratio, distor tion and other vital
performance parameters. The overall
result is a stereo amplifier with superb
characteristics.
Balanced connection reliably blocks
induced noiseFig. 1 C-245 block diagram

The longer the cable connections between
audio components, the higher is thedanger of external noise being introduced
into the signal path, which invariably leads
to sound quality degradation. The balanced
connection principle reliably prevents thisdanger, by keeping the signal transfer

n Line amplifiers and balanced input/
output amplifiers arranged on PCB
motherboard (total 10 modules)n Supplied remote commander RC-20
Allows volume adjustment and source
switching.

completely free from any kind ofinterference.
Modular construction keeps amplifier
circuits separate
The six line amplifiers and balanced output
amplifiers are housed in a total of 10 separate
modules neatly arranged on a motherboard.
The units are firmly secured with a frame
construction to prevent external vibrations
from affecting the sound.

Tone controls use summing
active filters for highest sound quality
The tone control circuitry in the C-245 wasspecially designed with summing active filterssuchasfound inhigh-quality
graphic
equalizers.
Figure 6 illustrates
the operation principle of thisTone control characteristics
circuit. The
flat signal is passed straight through, and only
when an adjustment is required, the characteristics are created at F1 and F2 and added toTriple parallel unit amplifier

Input

OutputComplete mono construction with separatetransformers for left and right channels
The power supply of the C-245 employs a dualmono approach with separate powertransformers and filtering capacitors for thetwo stereo channels. Each unit amplifier isequipped with a wide-range low-impedance
voltage regulator to eliminate any possibilityof interference between stages.

Fig. 6 Tone control circuit diagram(summing active filter type)the signal, thereby producing the desiredchange. This design provides efficient control
without degrading signal purity.
Logic-controlled relays for signal switchingassure high sound quality and long-term
reliability
The use of logic-controlled relays at strategic
locations makes it possible to keep signal
paths extremely short. The relays used in theC-245 are high-performance hermeticallysealed types as used in professional
communication applications. The contacts are
twin crossbar types plated with gold and silver
palladium alloy, for minimum contact
resistance and outstanding long-term
reliability.

Sealed relays directlyconnected to gold-plated input/output connectors

Option Boards

Other features and functionsn Option board available for direct digital signal input for high-grade CD reproductionn Option board available for analog record reproductionn High-quality volume control. Supplied remotecommander for volume adjustment andsource switching.
n High carbon cast-iron insulator feet for highsound qualityn Dedicated headphone amplifier for optimum
soundDigital Input BoardDAC-10

Three types of option boards are available for the C-245: Digital Input Board DAC-10, Analog Input Board AD-10, and LineInput Board LINE-10. Insert the desired board in a rear-panel
option board slot.

This board features an MDS (Multiple Delta Sigma)
D/A converter and has inputs for coaxial and opticalfiber connections.

m The DAC-10 cannot be used in the models E-407, E-406V,E-306V, E-211, C-265.

It can accept the digital output signal from components suchas a CD player, MD recorder, DAT recorder, etc. (sampling
frequency range 32 - 96 kHz, 24 bits).

m The Analog Disc Input Board AD-9 and the Line Input Board
LINE-9 can also be used.

Analog Disc Input Boardn EXT PRE function permits use of external
preamplifier for playback

AD-10This board contains a high-performance, high-gain
phono equalizer.

n Loudness compensator for enhanced bass
at low listening levels

Internal DIP switches control MM/MC operation, MC input
impedance, and subsonic filter on/off.

MMMC

Gain
: 36 dB
Input impedance : 47 kilohms
Gain: 62 dB
Input impedance : 10/30/100 ohms
(selectable)

Line Input Board

LINE-10

This option board provides an additional set of conventional
unbalanced line inputs which can be used to connect a CD
player, tuner, or other component with analog output.

Compensator response
Option board shown in photo is DAC-10

n Front panel

GUARANTEED SPECIFICATIONS[Guaranteed specifications are measured according to EIA standard RS-490.]m Frequency Response

BALANCED/UNBALANCED INPUT
3 - 300,000 Hz +0, -3.0 dB
20 - 20,000 Hz +0, -0.2 dB

m Total Harmonic Distortion(for all inputs) 0.005%

m Input Sensitivity, Input ImpedanceSensitivity
For rated output
For 0.5 V output
252 mV63 mV
252 mV
63 mVInput
BALANCEDUNBALANCED
m Rated Output,Output Impedance

Input impedance
40 kΩ
20 kΩ

BALANCED/UNBALANCED OUTPUT 2 V, 50 ohms
TAPE REC 252 mV, 200 ohms

m Signal-to-Noise Ration Rear panel

Input

Input shorted, IHF-A weighting
S/N ratio (EIA)
S/N ratio at rated input

BALANCEDUNBALANCED

Option board
expansion slots

108 dB
121 dBm Maximum Output Level (0.005% THD, 20 - 20,000 Hz)
BALANCED/UNBALANCED OUTPUTTAPE RECm Minimum Load Impedance

BALANCED/UNBALANCED OUTPUTTAPE RECm Gain
BALANCED/UNBALANCED INPUT ➞ BALANCED / UNBALANCED OUTPUTBALANCED/UNBALANCED INPUT ➞ REC OUTPUT★
A INPUT SELECTOR
B Function LED indicators
C VOLUME Control
D PHONES Jack
E POWER Switch
F EXT PRE and output ON/OFF Switch
G BASS Control
H TREBLE Control
I TONE Controls ON/OFF Button
J COMP (Compensator) ON/OFF Button
K TAPE COPY Selector 1➞2 OFF 2➞1L TAPE RECORDER SelectorRECOFFSOUCE12M BALANCE Control
N STEREO/MONO Button
O Attenuator Button
P Line inputs
Q TAPE 1, 2 Play/Record ConnectorsR OUTPUTS (Unbalanced)
S EXT PRE (External Preamplifier) input(Unbalanced)
T CD/LINE INPUTS (BALANCED)
21 OUTPUTS (Balanced)
U
22 EXT PRE (External Preamplifier) Inputs
U(Balanced)
23 AC Power Supply Connector★
URemarks★ This product is available in versions for 120/230 V AC. Make sure that the voltage shown on
the rear panel matches the AC line voltage in your area.
★ The shape of the AC inlet and plug of the supplied power cord depends on the voltage rating
and destination country.

n Supplied accessories:

Residual noise
1.0 µV
1.0 µV

97 dB
97 dB
:
:

5.0 V
5.0 V::

600 ohms
10 kilohms::

18 dB0 dB

m Loudness Compensation+6 dB (100 Hz)

m Tone Controls

Turnover frequency and adjustment range
BASS: 300 Hz ±10 dB (50 Hz)
TREBLE:
3 kHz ±10 dB (20 kHz)m Attenuator-20 dBm Headphones Jack

Suitable impedance: 8 - 100 ohms

m Power Requirements

AC 120 V / 230 V (Voltage as indicated on rear panel)
50/60 Hzm Power Consumption

16 watts

m Maximum Dimensions

WidthHeightDepthm Weight

16.8 kg (37.0 lbs) net
21.0 kg (46.3 lbs) in shipping carton

475 mm (18-11/16")
150 mm (5-7/8")
409 mm (16-1/8")

m Supplied Remote Commander RC-20
Remote control principle: Infrared pulse
Power supply : 3 V DC (IEC R6 batteries × 2)
Dimensions : 55 mm (W) x 194 (H) x 18 (D) mm
Weight: 100 g (including batteries)• AC power cord
• Audio cable with plugs (1 m)• Remote commander RC-20• Specifications and design subject to change without notice for improvements.

http://www.accuphase.com/K015Y

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