CLASS-AB STEREO
POWER AMPLIFIER

P-4600Accuphase Laboratory, Inc.

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When Accuphase introduced the P-300 power amplifier in1973, its power and driving capability were a very big
surprise to the market.

The P-4000 series is the standard category of the class-AB
power amplifier which is in the tradition of P-300. The newP-4600 is the fourth generation since the P-4100 wasreleased in 2008 and has greatly improved its performanceand ease of use over the generations.
The P-4600 has a significantly increased maximum output
compared to its predecessor, with specifications of 150
watts into 8 ohms, and its high damping factor allows it todrive all speakers flawlessly.
The low-noised balanced circuit operation with theinstrumentation amplifier can extract information from any
music source. The P-4600 vividly reproduces theperformer’s emotion and the atmosphere of the stage.

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Dimensions and Weight• Unit dimensions are the same as P-4500
Weight is slightly heavier– Width 465mm– Height 190mm– Depth 427mm– Weight 30.0kg

Accuphase Laboratory, Inc.

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The dimensions of the P-4600 are the same as the P4500, and the weight is a little heavier, it weighs 30.0kg.
** P-4500: Width 465mm, Height 190mm, Depth 427mm,
Weight 29.2kg

2Front and Rear View
Aluminum Top plate

Front View
Rear View

Speaker, Meter Display Selector

Gain Selector

Two pairs of large speaker terminals

Accuphase Laboratory, Inc.

3The P-4600 is equipped with large analog “needle” meterswhich offer an output power monitor with good visibility.
They are high-sensitivity of the -50dB indicator, which allows
you to enjoy the upbeat needle move even under the low
volume operation.
We also put the gain selector in the front panel,
You can choose the appropriate gain level from the 4 settings,“Max, -3dB, -6dB, and -12dB.”
The P-4600 also has two independent speaker terminals,
making it easy to use different types of speakers.
The gain switching does not attenuate the signals with anattenuator. However, it controls the gain at the input amplifier
section, making the power amplifier section stable andreducing the residual noise when using high-efficiency
loudspeakers. We can simultaneously decrease the noise,
which occurs when operating the unit under a low gain level.

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Internal View
Lch Power amp engine

Rch Power amp engine

50000uF Custom-madeFiltering Capacitor
High-efficiency large troidaltransformer

Accuphase Laboratory, Inc.

4P-4600 has a mono-block construction.
It contains an intense power supply with a massive
special-made and high-efficiency toroidal transformer andtwo sizeable 50000μF filtering capacitors in the center ofthe unit.
In addition, the two power amplifier units are kept
separate for the left and right channels.

4High Output Power• Class-AB 150W / 8Ω, 450W / 2ΩP-4500P-4600

8Ω
4Ω2Ω

90W

150W

300W

180W

360W

450W

Rated Output power

Accuphase Laboratory, Inc.

5The high-power design provides the rated output power of150W/8Ω, 300W/4Ω, and 450W/2Ω that vastly exceeds
conventional models, securing an overwhelming dynamicrange.

5Technology for High Output Power• 6 Parallel Output stage per channel (P-4500: 4 parallel)High output Bipolar transistor(150W 15A)

Power Amplifier Engine

Accuphase Laboratory, Inc.

6The P-4600 power amplification stage uses a 6-parallelpush-pull power transistor architecture. By connecting
output elements in parallel, the output impedance islowered to improve the driving capability. And the sametime, the load per transistor is reduced and it enables
power to be supplied with a margin of safety under allconditions.

6Ultra Low Noise• High power but low noise– S/N ratio: 125dB guarantee (P-4500: 121dB)

P-4500P-460023.9uV

19.5uV
18% Down
Guaranteed output noise

Accuphase Laboratory, Inc.

7The noise performance of the P-4600 is remarkable
compared with the former P-4500.
With the state-of-the-art circuitry, the P-4600 improves noiselevel suppression by 17% over the previous model as
guaranteed spec.
The guaranteed S/N ratio achieves 125dB, which is 4dB ofperformance improvement over P-4500.

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Technology for ultra low noise• Instrumentation Amplifier architecture• Balanced signal transfer with the optimization ofgain distribution

Balanced Input Module

Signal Input Section

Accuphase Laboratory, Inc.

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With balanced circuits in the signal input section, theamplification stage entirely comprises an instrumentation
amplifier principle that equalizes input impedance on the + and –sides for excellent external noise suppression and provides
optimal circuitry for this high-end audio amplifier.

Noise Level suppression has been dramatically improved byassigning a high gain (12.6x) in the signal input section withexcellent noise figure results.

8Super high Damping Factor• Increase Damping Factor for high driving ability– Damping Factor: 800 guaranteed

P-4500700
500P-4600

800
1000

800

Guaranteed Damping Factor
800

Accuphase Laboratory, Inc.

9The P-4600 achieves 800 of guaranteed Damping Factor,
significantly improved driving capability compared toprevious models*Damping Factor, DF: The damping factor is an index ofspeaker driving ability. A Higher Damping-Factor amplifier
has a higher speaker driving ability. DF = 8 ohm / Outputimpedance

9Technology for super high Damping Factor• Speaker protection equipped with MOSFET switch circuit• Short signal path configuration

Large speaker terminals

Protection circuit Assembly

MOS-FET switch
On-resistance: 1.6mΩ

Accuphase Laboratory, Inc.

10Mechanical relays are the typical components for speakerprotection. Still, the contact resistance of mechanicalrelays is higher than people think.
Therefore, Accuphase has chosen the MOS-FET switch
instead of conventional mechanical relays for speakerprotection.
Thanks to this MOS-FET switch, the damping factor,
reliability, and sound quality are improved.
The P-4600 employs carefully selected very lowimpedance components such as the large speakerterminals. Making signal paths thick and short also helps
to attain low impedance.
** MOS-FET switch On-resistance
P-4600’s MOS-FET: 1.6mΩ
P-4500’s MOS-FET: 2.0mΩ

10Technology for super high Damping Factor• Balanced Remote sensing– Feedback from speaker terminal proximity– Signal-line and GND-line sensing
Signal sensing
Speaker terminal+ Signal- GND
Power Amplifier

GND sensing

Accuphase Laboratory, Inc.

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“Remote Sensing” is the technique to lower the output
impedance of the amplifier by the negative feedback witha signal sensing from nearby the speaker terminals.
“Balanced Remote Sensing” is the technique to make theoutput impedance even lower by both the signal sensing
and the GND sensing, that is, the negative feedback ofthe GND level.
Not only the Damping Factor but also the Total Harmonic
Distortion and Intermodulation Distortion are all improvedby the Balanced Remote Sensing.

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Pursuing further product safety and reliability• Power amplifier– Protection circuit using Photo-couplers for terminal short– Temperature sensors are installed on the heatsink

Temperature-sensor

Photo-coupler

Accuphase Laboratory, Inc.

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The newly designed output protection circuit can detect
any short-circuiting of the speaker terminals with due
consideration for product safety.
Temperature sensors that detect the heatsink
temperature are installed. Thanks to this, the unit
accurately ascertains the high-temperature alarm in thepower amplifier section.
Thanks to the photo-coupler, the detected signal iscompletely isolated from the output signal to minimize theadverse effects on the sound quality.
**When these protection circuits are activated, the unit
completely interrupts speaker output. It makes the power
meters flash to indicate the abnormal condition.

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