Accuphase P-4200 User Manual
●Output stage with triple parallel push-pull configuration for each channel
delivers high power down to very low impedance loads ●
amplifier principle used in input stage ●
topology in amplification stage ●
monophonic amplifier ●
Strong power supply with massive high-efficiency
MCS+ circuit and current feedback
Bridged connection mode allows upgrading to
toroidal transformer and large filtering capacitors ●
Instrumentation
4-stage gain control
I/V
converter
Trans-impedance amplifier
Current adder
–INPUT
+ INPUT
Current NFB
network
Buffer
Buffer
OUTPUT
Amplifier
–INPUT
OUTPUT
+ INPUT
+
–
+
–
–
+
NFB
NETWORK
NFB
NETWORK
NFB
NETWORK
Power amplifier stageSignal input stage
Principle of current feedback amplifier
Instrumentation amplifier configuration
■Power amplifier assembly with three
parallel push-pull high-power transistor
pairs per channel mounted directly to
large heat sink, MCS+ circuitry, and
current feedback amplifier.
Instrumentation amplifier configuration and further refined MCS+ topology
Balanced input phase
selector switch
●
If the balanced input of
the preamplifier uses
th e “ p in
w
p osi t ive ”
co n f ig u r at i o n, t hi s
switch can be used for
proper matching.
Accuphase’s original MCS (Multiple Circuit Summing)
principle u s e s a number o f i d e nt i c a l circuits
connected in parallel to achieve superio r p er for-
mance characteri stics. M CS+ is a f ur th er ref ined
version of this approach. By extending parallel opera-
tion to the class-A drive stage of the current/voltage
converter, the noise floor has been lowered further.
Further refined MCS+ topology for even
lower noise
Current feedback principle assures excellent
phase characteristics in high range
Instrumentation amplifier configuration
allows fully balanced signal paths
As shown in the illustration, the P-4200 uses the
output signal current rather than voltage for
feedback. Since the impedance at the current
feedback point is very low, there is almost no phase
shift. A minimal amount of NFB therefore results in
maximum improvement of circuit parameters.
The newly adopted “instrumentation amplifier”
principle ensures that 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 virtually
shut out. The result is a
drastic improvement in
operation stability and
reliability.
Ever since its founding in 1972, A ccuphase has
designed its power amplifiers for o ptimal speaker
drive, capturing the high-end market with a succession of highly regarded models that became legend.
The commemorative model A-20 0 released on the
occasion of the company’s 40th anniversar y demonstrated Accuphase’s mastery of power amplifier
technology. It stands at the pinnacle of its field and
has been widely lauded as a history-making achievement both in terms of per fo rm ance and sonic
exce llenc e. The Stereo Power Amplif ie r P- 4200
incorporates the outstanding design technology of the
A-200. Based on the P- 4100, it represents a f ull
model change with further enhanced overall circuitr y.
Latest instr umentat ion amplifier topol ogy is
implemented in the entire configuration of the P-4200,
allowing not only fully balanced signal paths from the
inputs onwards, but also the realization of a gain
control that effectively minimizes residual noise. The
power amplifier section features another Accuphase
specialty, namely the MCS+ topology in combination
with current feedback, ensuring outstanding S/N ratio
and superior electrical performance characteristics.
The output stage for each channel uses three pairs of
high-power transistors with a Pc rating of 220 watts,
arranged in a parallel push-pull configuration. This
ensures low output impedance. Stable operation is
achieved by mounting the devices to massive heat
sinks o n b oth sides of the c hassis, for eff icient
dissipation of thermal energy. As demonstrated by the
power rating of 50 0 watts per channel into 1 ohm
(music signals only), t he P-420 0 can easily drive
speakers with very low impedance, and speakers with
uneven impedance c ur ves are also handled with
aplomb. Using the P- 4200 in bridged mode creates a
monophonic amplifier with even more impressive
power output capability. This kind of performance is
sust ained by a power supply section with a large
toroidal transform er whose ef ficiency has been
further increased compared to the P-4100, and two
large 47,000 µF filtering capacitors selected for
ultimate sound quality and refl ecting know -h ow
gained with the A-200.
The output circuitr y also benefits from the latest
technology advances. Output relays have been
replaced by MOS-FET switches that combine excellent
reliability with highly pure amplification. Redesigned
output coils and other features result in lower energy
losses and allow a drastic improvement of the damping
factor to 500. This rating not only points towards an
extremely wide power bandwidth, it also means that
the degree of coupling between loudspeakers and
amplifier has been tightened even further, resulting in
music playback of impressive fidelity.
Stereo power amplifier with impeccable performance Instrumentation amplifier principle
in amplification stage allows fully balanced signal paths. Further refined MCS+ and current
feedback topology assure excellent sound, with outstanding S/N ratio and excellent performance in all other aspects. A hefty power supply and power transistors arranged in a triple
parallel push-pull configuration deliver 500 watts/ch (music signals) into an ultra-low 1-ohm
load. Output stage with further lowered impedance results in a damping factor of 500.
■Power modules with high-power transistors in triple
parallel push-pull arrangement deliver linear power of
500 watts per channel into 1 ohm (music signals only),
360 watts into 2 ohms, 180 watts into 4 ohms, or 90
watts into 8 ohms.
■Large, high-efficiency toroidal transformer and two
47,000 µF aluminum electrolytic capacitors selected for
best sonic performance.
■Output stage with further lowered impedance
realizes damping factor of 500.
■Bridging allows upgrade to monophonic amplifier
with even higher power, delivering 1,000 watts
into 2 ohms (music signals only), 720 watts into 4
ohms, or 360 watts into 8 ohms.
■ Input selector button on front panel allows
switching between Line and Balanced signals.
■4-stage gain selector (MAX, -3 dB, -6 dB, -12 dB)
also minimizes residual noise.
■Large analog power meters with on/off switch
and peak hold function (3 seconds/infinite).
■Semiconductor (MOS-FET) switches used for pro-
tection circuitry prevent contact
problems and ensure long-term
reliability. Eliminating mechanical contacts f rom signal path
also f ur ther en ha nces so un d
quality.
■Two sets of oversize speaker
terminals also accept Y lugs.
MOS-FET switches
Large speaker terminals
Parts selected for high sound quality and reliability
High-power transistors used in output stage
Toroidal power transformer
Input selector button
Assembly with meter and protection circuitry etc.
Filtering capacitors
Gain selector Meter selector
Assembly with line and balanced input connectors
Signal input stage
+
INPUT
GAIN CONTROL
CIRCUIT
INPUT
＋
−
NETWORK
NETWORK
−
＋
MCS+
（Multiple Circuit Summing）
Bias
stabilizer
circuit
Q
1
Q
Q
5
9
Q
Q11Q
7
Q
NFB
NFB
3
Bias
stabilizer
circuit
Bias
stabilizer
circuit
Q
2
Q
Q10Q
6
Q
Q12Q
8
Q
4
Bias
stabilizer
circuit
Figure 1 Circuit diagram of amplifier section (one channel)
Power amplifier stage
Q
13
15
14
16
NFB
NETWORK
REGULATOR
Q
17
stabilizer
circuit
Q
18
REGULATOR
550
+B1
+B2
Q
21
Q
22
Q23Q25Q
Q24Q26Q
B1
27
28
OUTPUT
Max. output power
Rated output power
Q
19
Bias
Q
20
500
450
400
350
300
250
Output power (W)
200
150
100
B2
50
243W
152W
180W
180W
90W
90W
8Ω 4Ω 2Ω 1Ω
Impedance (Ohms)
389W
360W
360W
512W
500W
500W
Figure 2 Output power characteristics
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