Accuphase P-3000, P-3921 Brochure

m Triple parallel push-pull output stage in each channel delivers

plenty of linear power even into very low load impedances

m Instrumentation amplifier derived signal path design
m Advanced MCS+ circuit topology m Bridged connection mode

allows upgrading to true monophonic amplifier m Massive Super
Ring toroidal transformer rated for 700 VA m 4-step gain control

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.

MCS+

Multiple Circuit

( )

+

B

3

+

INPUT

–

INPUT

+
–

GAIN CONTROL

CIRCUIT

–
+

NFB

NETWORK

NFB

NETWORK

–

B

3

Summing

Bias stabilizer

circuit

Q

1

Q

5

Q

Q

Q

Q

7

3

Bias stabilizer

circuit

Bias stabilizer

circuit

2

Q

6

Q

8

4

Bias stabilizer

circuit

Note 1 Low amplifier output impedance

When 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 principle

Even 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.

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 virtually shut out. The result

Signal input stage Power amplifier stage

+

–

NFB

GAIN CONTROL

CIRCUIT

NETWORK

NFB

NETWORK

–
+

+
–

Instrumentation amplifier configuration

REGULATOR

13

Q

15

14

16

17

Bias stabilizer

circuit

Q

18

NFB

NETWORK

REGULATOR

Fig. 1 Circuit diagram of amplifier section (one channel)

OUTPUT

+

B

1

Q

Q

19

Q

20

Q

21

Q

Q

22

–

B

1

Q

9

Q11Q

Q10Q

Q12Q

+

INPUT

–

INPUT

Q

20

10

Output current (A)

0

0 8 16 24 32 40

Output voltage (V)

★1 ohm rating is for music signals only.

Fig. 2 Load impedance vs. output power

(Output voltage/output current)

400W

1Ω

330W

2Ω

4Ω

220W

8Ω

16Ω

133W

71W

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

+

B

Q

23

25

2

the noise floor.

Triple parallel push-pull power
unit delivers guaranteed linear
power output of 300 watts into

OUTPUT

2 ohms, 150 watts into 4 ohms,
and 75 watts into 8 ohms

The output stage uses high-power
transistors with a rated collector

Q

24

26

–

B

2

dissipation of 130 watts. These
devices feature excellent frequency
response, current amplification
linearity, and switching
characteristics. The transistors are
arranged in a triple parallel push­pull configuration and mounted on
a massive heat sink. This assures