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Stereo power amplifier is ideal match for C-2400 MCS technology in
input stage improves S/N ratio, distortion ratings and other characteristics.
6 pairs of wide-band high-power transistors in parallel push-pull
configuration for each channel. Massive 1 kVA toroidal power transformer
supports 650 watts of power into ultra-low 1-ohm impedance. 4-step gain
control effectively reduces noise.
The P-5000 continues the distinguished design
policy of the M-8000 and P-7000. This stereo
power amplifier uses carefully selected top
quality parts throughout and is an ideal match
for the C-2400 preamplifier. MCS topology in
the input stage reduces noise even further.
Refined technology and inspired design result
in superb performance and flawless sound
quality.
In order to drive any kind of speaker with
precision and authority, a power amplifier must
provide extremely low output impedance
(Note 1) and be capable of supplying a
constant drive voltage at all times (Note 2). To
realize these design goals, a power supply
that fully meets the demands of the output
stage is necessary. In the output stage of the
P-5000, six pairs of high-power transistors with
a rated collector dissipation of 150 watts are
arranged in a parallel push-pull configuration
for each channel. The devices are mounted to
large heat sinks for efficient dissipation of
thermal energy. Rated output power into 1 ohm
is 650 watts per channel (music signals only).
Power remains linear also when impedance
changes, as exemplified by the rating of
400 watts into 2 ohms, 200 watts into 4 ohms
and 100 watts into 8 ohms. Even speakers
with very low impedance or with drastic
impedance fluctuations can be driven
effortlessly and accurately. By using the P-5000
in bridged mode, it is possible to create a
monophonic amplifier with even higher power
reserves. This performance is sustained by a
massive high-efficiency Super Ring toroidal
transformer and large filtering capacitors.
The important input stage also has been given
due attention. Another Accuphase innovation
called MCS (Multiple Circuit Summing) helps
to minimize noise. Current feedback topology
assures totally stable operation up to very high
frequencies. Balanced inputs shut out external
noise. The copper foil side of the PCBs and all
input and output terminals and major signal
carrying points are gold plated, for enhanced
signal purity.
BIAS STABILIZER
CIRCUIT
BIAS STABILIZER
CIRCUITBIAS STABILIZER
CIRCUIT
Note 1: Low amplifier output impedanceWhen forming the load of a power amplifier a loudspeaker
generates a counterelectromotive force that can flow back into
the amplifier via the NF loop. This phenomenon is influenced by
fluctuations in speaker impedance and interferes with the drive
performance of the amplifier. The output impedance of a power
amplifier should therefore be made as low as possible by using
output devices with high current capability. This absorbs the
counterelectromotive force generated by the voice coil and
prevents the occurrence of intermodulation distortion.
Note 2: Constant drive voltage principleEven when the impedance of a load fluctuates drastically, the
ideal power amplifier should deliver a constant voltage signal to
the load. Figure 2 is a graph plotting the output voltage versus
current characteristics. Even when the load changes, the output
voltage remains almost constant, showing linear current
progression. Actual measurement of clipping power at the
extremely low load impedance of 1 ohm yields 660 watts. At 2
ohms, the figure is 500 watts, at 4 ohms 310 watts, and at 8
ohms 171 watts. This demonstrates the impressive performance
reserves of this amplifier.
6-parallel push-pull power unit delivers guaranteed
linear power output of 400 watts into 2 ohms, 200
watts into 4 ohms and 100 watts into 8 ohms
The output stage uses high-power transistors with
a rated collector dissipation of 150 watts and
collector current of 15 amperes. These devices boast
excellent frequency response, current amplification
linearity, and switching characteristics. The
transistors are arranged in a 6-parallel push-pull
configuration (Figure 1) for ultra-low impedance and
mounted on a massive heat sink made from diecast
aluminum. This assures effective heat dissipation
and reduces the impedance of the output stage.
Power linearity is maintained down to ultra-low loads,
which demonstrates the impressive capabilities of
this amplifier.MCS topology in input stage reduces residual noise
and drastically improves S/N ratio
The input stage features Accuphase's original MCS
(Multiple Circuit Summing) design. Three separate
unit amplifiers for the input signal are connected in
parallel, minimizing noise and distortion and greatly
improving other performance parameters as well.
This approach yields further improved sound quality.
NFB switching type gain control
reduces residual noise
Because the current feedback
type amplifier circuitry is very
stable and introduces little phase
shift, an NFB switching gain
control has become possible
(MAX, -“3 dB, -“6 dB, -“12 dB).
With this approach, reducing gain
also results in reduced noise.
This is especially beneficial when
using highly efficient speaker
systems where the noise floor
could be a problem.
Fig. 2 Output power vs. load impedance(output voltage/output current: actual measurements)
* 1-ohm operation possible with
music signals only Output voltage (V)
Output current (A)
Fig. 1 Circuit diagram of amplifier section (one channel)

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Current feedback circuit topology prevents phase
shifts in high frequency range
The P-5000 employs the renowned current feed-
back principle developed by Accuphase. At the sens-
ing point of the feedback loop, the impedance is
kept low and current detection is performed. An
impedance-converting amplifier then turns the cur-
rent into a voltage to be used as the feedbacksignal. Since the impedance at the current feed-
back point (cur-
rent adder in
Figure 3) is
very low, there
is almost no
phase shift.
Phase com-
pensation can
be kept to a
minimum, re-
sulting in excel-
lent transient response and superb sonic transpar-
ency. Minimal amounts of NFB are used to maximum
effect, providing natural energy response.
Figure 4 shows frequency response for different
gain settings of the current feedback amplifier. The
graphs demonstrate that response remains uniform
over a wide range.Robust power supply with "Super Ring" toroidal
transformer and high filtering capacity
The P-5000 features a massive toroidal power trans-
former with a maximum rating of 1 kVA. The trans-
former is housed in
a non-resonant alu-
minum case filled
with a material that
transmits heat and
absorbs vibrations.
This completely pre-
vents any adverse
influences on other
circuit parts. A tor-
oidal transformer
uses heavy-gauge
copper wiring on a
doughnut-shaped
core, resulting in
low impedance and
high efficiency while
allowing compact
dimensions. Two ul-
tra-large aluminum
electrolytic capaci-
tors rated for
47,000 ÂµF each
serve to smooth out the pulsating direct current
from the rectifier, providing more than ample filter-
ing capacity.
n nn n
nPower amplifier assembly with 6 parallel push-
pull transistor pairs per channel mounted directly
to large aluminum diecast heat sinks, MCS
circuitry, and current feedback amplifier
Fig. 4 Frequency response with current
feedback I-V
converter
Current NFB
network Amplifier Output
Trans-impedance
amplifier Current
adder -“ Input
Buffer
+ Input
Buffer
Fig. 3 Current feedback amplifier principle diagram