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A stereo power amplifier with impressive punch: 1,000 watts into 1 ohm
MCS technology in input stage improves S/N ratio, distortion ratings and
other characteristics. 11 pairs of wide-band high-power transistors in parallel
push-pull configuration for each channel. Power supply with massive 1.5 kVA
toroidal power transformer supports linear power down to impedances as
low as one ohm. Teflon PCBs with low dielectric constant and minimum loss.
The P-7000 continues the distinguished design policy
of the M-8000. It adds MCS technology in the input
stage and many other refinements. Carefully
selected top quality parts are used throughout. The
design aim was to achieve very low output impedance
(Note 1) and constant drive voltage (Note 2). The
end result is a stereo power amplifier that provides
effortless performance and impeccable sound quality.
In the output stage, 11 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 on both sides of the
main chassis for efficient dissipation of thermal
energy generated during operation. As a result, the
amplifier is capable of delivering power in a linear
progression towards lower load impedances: 1,000
watts into 1 ohm, 500 watts into 2 ohms, 250 watts
into 4 ohms and 125 watts into 8 ohms. Speakers
with very low impedances as well as speakers whose
impedance fluctuates drastically can also be driven
with ease. By using the P-7000 in bridged mode, it
is possible to create a monophonic amplifier with
even higher power. This performance is sustainedby a massive Super Ring toroidal transformer housed
in a diecast enclosure with directly mounted heat
sinks, and by large filtering capacitors. The
transformer is rated for 1.5 kVA, and there are two
capacitors of 56,000 µF each. This assures more
than ample reserves and allows the amplifier to
meet even the most demanding and rapidly
fluctuating power requirements.
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 combines total operation
stability with excellent frequency response, while
requiring only minimum amounts of negative
feedback. The material used for printed circuit boards
has a decisive influence not only on electrical
characteristics but also on the sonic end result.
The P-7000 uses Teflon boards with extremely low
dielectric constant and low loss. The copper foil
side of PCBs and all input and output terminals as
well as all major signal carrying points are gold
plated. Balanced inputs help to shut out external
noise. The overall result of these measures is musical
purity that leaves nothing to be desired.11-parallel push-pull power unit delivers guaranteed
linear power output of 1,000 watts into 1 ohm, 500
watts into 2 ohms, 250 watts into 4 ohms and 125
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 an 11-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 allows the
amplifier to effortlessly handle very low impedances.
Power linearity is maintained down to loads as low as
1 ohm, which demonstrates the impressive
capabilities of this amplifier.
MCS topology in input stage drastically improves
S/N ratio, distortion, and other characteristics
The input stage features Accuphase's original MCS
(Multiple Circuit Summing-up) design. Three separate
– B1
Q21 Q23 Q25 Q27 Q29 Q31 Q33 Q35 Q37 Q39 Q41 Q43
Q24 Q20 Q22
Q19
Q26 Q28 Q30 Q32 Q34 Q36 Q38 Q40 Q42 Q44
Q18
Q16
Q17
Q15
Q14
Q13
OUTPUT +
–
INPUT–
INPUT+
MCS (Multiple Circuit Summing-up)
Q9-12
Q1-4
Q5-8 IC2
IC1
IC3
NFB
NETWORK
REGULATOR
REGULATOR
+ B1
– B2
+ B2
BIAS STABILIZER CIRCUIT
BIAS STABILIZER
CIRCUIT
BIAS 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 1,050 watts. At 2
ohms, the figure is 606 watts, at 4 ohms 326 watts, and at 8 ohms
170 watts. This demonstrates the impressive performance reserves
of this amplifier.
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)
unit amplifiers for the input signal are connected in
parallel, which minimizes noise and
distortion and greatly improves other
performance parameters as well. This
manifests itself in further improved
sound quality.
Current feedback circuit topology
prevents phase shifts in high
frequency range
The P-7000 employs the original
Accuphase current feedback principle.
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
Fig. 1 Circuit diagram of amplifier section (one channel)