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0 10 20
0 8 16 24 32 40
400W
330W
220W
133W71W 1-„¦
2-„¦
4-„¦
8-„¦
16-„¦
Output current (A)
Output voltage (V)
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 400 watts. At 2 ohms, the figure is 330 watts, at 4
ohms 220 watts, and at 8 ohms 133 watts. This demonstrates the
impressive performance reserves of this amplifier.
Fig. 2 Load impedance vs. output power
(Output voltage/output current)
-˜…1 ohm rating is for music signals only.
Power amplifier with instrumentation amp
configuration
The P-3000 features a new "instrumentation
amplifier" principle whereby all signal paths from the
inputs to the power amp stage are fully balanced.
This results in excellent CMRR (common mode
rejection ratio) and minimal distortion. Another
significant advantage is that external noise and other
external influences are vir tually shut out. The result
A stereo power amplifier capable of delivering 400 watts into 1 ohm (with music
signals) Fully balanced signal paths as found in high-quality instrumentation
amplifiers. Further refined MCS+ topology and current feedback
design. Improved S/N ratio, minimal distortion, and great
performance in all other areas. Power supply with massive
700 VA toroidal transformer and triple parallel push-pull
arrangement of high-power transistors in each channel.
The P-3000 is based on the same design
technology as the renowned P-7000 and
P-5000 models. Using only carefully selected top
quality parts throughout, the P-3000 is an ideal
match for the C-2000 preamplifier.
A new feature in the P-3000 is the fact that all
signal paths from the input terminals onwards are
fully balanced, an approach otherwise found only
in instrumentation amplifiers of the highest quality.
In addition, the power amplifier section employs
an improved version of MCS called MCS+
(Multiple Circuit Summing plus), as well as the
famous Accuphase current feedback topology.
S/N ratio, distortion, and other electrical
characteristics are further improved. And of
course, these refinements manifest themselves
in even better 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 constant-voltage
capability over the entire frequency range, a
powerful output stage supported by a capable
power supply are necessary.
In the output stage of the P-3000, three pairs of
high-power transistors are arranged in a parallel
push-pull configuration for each channel. The
devices are mounted to large heat sinks on both
sides for efficient dissipation of thermal energy.
Rated output power into an ultra-low impedance
of 1 ohm is 400 watts per channel (music signals
only). Power remains linear also when impedance
changes, as exemplified by the rating of 300 watts
into 2 ohms, 150 watts into 4 ohms and 75 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-3000 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.
OUTPUT
+ B3
-“ B3
-“INPUT
+INPUT
NFB
NETWORK
NFB
NETWORK
GAIN CONTROL
CIRCUIT
+
-“
-“
+
REGULATOR
REGULATOR
+ B1
-“ B1
-“ B2
+ B2
Q1
Q3
Q2
Q4 Q8
Q6
Q7
Q5 Q9
Q17 Q19
Q18 Q20
Q21
Q22
Q23
Q24
Q25
Q26
Q13
Q11 Q15
Q10 Q14
Q12 Q16
NFB
NETWORK
MCS+Multiple Circuit
Summing( ) Bias stabilizer
circuit
Bias stabilizer
circuit
Bias stabilizer
circuit
Bias stabilizer
circuitBias stabilizer
circuit
Fig. 1 Circuit diagram of amplifier section (one channel)
+
-“
-“INPUT
NFB
NETWORK
GAIN CONTROL
CIRCUIT
NFB
NETWORK
OUTPUT
+INPUT +
-“
+ -“
is a drastic improvement in operation stability and
reliability.
Further refined MCS+ topology
Accuphase's original MCS (Multiple Circuit Summing)
principle uses a number of identical circuits
connected in parallel to achieve superior
performance characteristics. The MCS+ is a further
refined version of this approach. Improvements in
the bias circuitry of the input-stage
buffer amplifier result in greater
stability. This in turn makes it
possible to extend the parallel
operation approach to the class-A
drive stage of the current/voltage
converter, thereby further lowering
the noise floor.
Triple parallel push-pull power
unit delivers guaranteed linear
power output of 300 watts into
2 ohms, 150 watts into 4 ohms,
and 75 watts into 8 ohms
The output stage uses high-power
transistors with a rated collector
dissipation of 130 watts. These
devices feature excellent frequency
response, current amplification
linearity, and switching
characteristics. The transistors are
arranged in a triple parallel push-
pull configuration and mounted on
a massive heat sink. This assures
Instrumentation amplifier configuration
Signal input stage Power amplifier stage
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effective heat dissipation and reduces the
impedance of the output stage.
Current feedback circuit topology prevents phase
shifts in high frequency range
The P-3000 employs the renowned current feedback
principle developed by Accuphase. At the sensing
point of the feedback loop, the impedance is kept
low and current detection is performed. An
impedance-converting amplifier then turns the
current into a voltage to be used as the feedback
signal. Since the impedance at the current feedback
point (current adder in Figure 3) is very low, there is
almost no phase shift. Phase compensation can be
kept to a minimum, resulting
in excellent transient response
and superb sonic transparency.
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-3000 features a massive toroidal power
transformer with a maximum rating of 700 VA. The
transformer is housed in a case filled with a material
that transmits heat and absorbs vibrations. This
Gain(Large)
(High) Frequency
completely prevents any
adverse influences on other
circuit parts. A toroidal transformer
uses heavy-gauge copper wiring on a
doughnut-shaped
core, resulting in
low impedance and
high efficiency while
allowing compact
dimensions, which
is especially useful
for audio appli-
cations.
Two ultra-large
aluminum
electrolytic
capacitors rated for
47,000 µF each
serve to smooth out
the pulsating direct
current from the
rectifier, providing
more than ample
filtering capacity.
BufferCurrent
adder
I-V
converter
Trans-impedance
amplifier Amplifier Output
Current NFB
network -“ Input
Buffer + Input
Fig. 3 Principle of current feedback amplifier
nPower amplifier assembly with
3 parallel push-pull transistor
pairs per channel mounted
directly to large heat sink,
MCS+ circuitry, and current
feedback amplifier
Fig. 4 Frequency response with current feedback(Response remains uniform also when gain changes)
