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Stereo power amplifier capable of delivering 500 watts into 1 ohm (music
signal) - Instrumentation ampli er principle allows fully balanced signal paths.
Further refined MCS+ and current feedback topology assure outstanding
S/N ratio, minimum distortion, and excellent performance in all other aspects,
resulting in superb sound quality. 3-parallel push-pull arrangement of high-
power transistors in each channel, sustained by power supply with massive
950 VA toroidal transformer. 4-step gain control minimizes residual noise.
The P-4100 is a stereo power amplifi er that takes
sophisticated sound to the next level. While
inheriting design technology from highly renowned
Accuphase models such as the P-7100 and M-6000,
the new model features instrumentation amplifi er
topology and a refi ned MCS+ circuit to lower the
noise fl oor even further. Only specially selected
top-grade materials and parts are used throughout
with impressive results.
In order to bring out the full potential of the
loudspeakers, an amplifi er must be able to cope
with drastically fluctuating speaker impedance
conditions. This can only be achieved by ensuring
constant drive voltage at all times. In other words,
the output impedance of the amplifi er must be kept
very low. This also makes it possible to absorb
the counterelectromotive force generated by the
voice coil, thereby eliminating a major source of
intermodulation distortion.
The P-4100 achieves these design goals with ease.
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 confi guration. This
ensures low output impedance. Stable operation
is achieved by mounting the devices to massive
heat sinks on both sides of the chassis, for effi cient
dissipation of thermal energy. As demonstrated by
the power rating of 500 watts into 1 ohm (with music
signals), the P-4100 can easily drive speakers with
very low impedance, and speakers with uneven
impedance curves are handled with complete
authority. Using the P-4100 in bridged mode creates
a mono amplifi er with even more impressive power
capability. The power supply section which acts as
energy source for the amplifi er employs a massive
950 VA toroidal transformer in combination with large
fi ltering capacitors, providing ample reserves even
with drastically fl uctuating loads.
The overall confi guration of the P-4100 employs the
latest instrumentation amplifi er principle, allowing
fully balanced signal paths throughout. In addition,
the power amplifi er section features refi ned MCS+
topology in combination with current feedback,
for further enhanced electrical performance
characteristics.
n Power modules with high-power transistors in 3-parallel push-pull
arrangement deliver 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.
n Amply dimensioned power supply with high-effi ciency toroidal transformer
and large fi ltering capacity.
The high-effi ciency toroidal transformer is rated for approx. 950 VA, and the two
extra-large 47,000μF aluminum electrolytic capacitors were selected for best sonic
performance.
n Bridged mode allows upgrading to monophonic amplifi er with 1,000 watts
into 2 ohms (music signals only), 720 watts into 4 ohms, or 360 watts into
8 ohms.
Bridged connection increases the output by a factor of 4, creating dramatic power
reserves in a monophonic confi guration.
n Four gain control settings minimize residual noise.The gain control alters gain in the fi rst stage of the instrumentation amplifi er. Four
settings are available (MAX, -3 dB, - 6 dB, -12 dB).
n Large analog power meters with on/off switch.
n Mode selector for easy switching between dual
mono/stereo/bridged operation.
n Fully balanced input stage
shuts out external noise
interference.
n Two pairs of oversize speaker
terminals accept also Y lugs
plugs.
Toroidal power transformer
Filtering capacitors
Gain selector
Parts selected for sound quality and reliability
* 1-ohm operation possible with music signals only
Output voltage (V)
Figure 2 Load impedance vs. output power (output voltage/output current) Figure 1 Circuit diagram of amplifi er section (one channel)
Output current (A)
MCS+ (Multiple Circuit Summing)
Instrumentation amplifi er
High-power transistors
in 3-parallel push-pull confi guration
Gain controlMeter on/off button Input selector
High-power transistors used in output stage
Assembly with unbalanced and balanced input connectors
Assembly with meter and protection circuitry Large speaker terminals
NFB
NETWORK
GAIN CONTROL
CIRCUIT
NFB
NETWORK
+ INPUT
- INPUT
Bias stabilizer circuit
Bias stabilizer
circuit
NFB
NETWORK REGULATOR
REGULATOROUTPUT
Bias stabilizer circuit Bias stabilizer
circuitBias stabilizer circuit
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Instrumentation amp confi guration allows
fully balanced signal paths
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.
Current feedback principle assures excel-
lent phase characteristics in high range
As shown in the illustration, the P-4100 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.
Further refi ned MCS+ topology for even
lower noise
Accuphases original MCS (Multiple Circuit
Summing) principle uses a number of identical
circuits connected in parallel to achieve superior
performance characteristics. MCS+ is a further
refined version of this approach. By extending
parallel operation to the class-A drive stage of
the current/voltage converter, the noise floor
has been lowered further.
n Power amplifi er assembly with three parallel push-pull
high-power transistor pairs per channel mounted directly
to large heat sink, MCS+ circuitry, and current feedback
amplifi er.
Instrumentation amplifi er confi guration
Signal input stage Power amplifi er stage
+
INPUT
- INPUT
Instrumentation amplifi er and further refi ned MCS+ topology
Principle of current feedback amplifi er
NFB
NETWORK
NFB
NETWORK
GAIN CONTROL
CIRCUIT OUTPUT
- INPUT
Buffer
+ INPUT
Buffer
I/V converter
Current NFB
network Trans-impedance amplifi er Current adder
Amplifi er
Output
