● Power amplification stage with 4-parallel complementary push-pull
configuration ● Linear output characteristics (90 W / 8 ohms, 180 W / 4 ohms,360 W / 2 ohms) ● 500 W output into ultra-low impedance load of 1 ohm(music signals) ● Instrumentation amplifier principle ● Current feedback
topology ● Balanced Remote Sensing ● High damping factor of 700● Speaker output protection with short-circuit detection ● Highly responsive
large peak power meters ● Support for bi-amping and bridged modeStereo power amplifier with outstanding performanceThe quest for the optimal power amplifier has just taken another giant leap forward. The P-4500
features an instrumentation amplifier configuration realized with discrete semiconductors in thesignal path, triple Darlington 4-parallel complementary push-pull architecture and many othertechnology advantages. The result is an impressive S/N ratio of 121 dB, rated output of 500 watts into
1 ohm (music signals), and a damping factor of 700. A newly developed output protection circuit canalso detect any short-circuiting of the speaker terminals, for complete peace of mind. This power
amplifier is the ultimate tool for immersive music enjoyment on the highest level.

Technology development ahead of the curve
Instrumentation amplifier principle realizes excellent S/N ratio and linear output characteristics■ Instrumentation amplifier topology further improves noiseperformance
The P-4500 employs an instrumentation amplifier configurationthat is highly effective in keeping external noise from affecting
the signal transmission lines. The configuration comprises a
signal input unit that receives the signal from the preamplifier anda power amplification unit that sends power to the speakers. The
input stage is designed for high gain (22 dB) and the power
amplification stage for low gain (6 dB). Consequently, the internalsignal has a large amplitude which makes it much less prone tointerference, thereby further improving the noise performance.
■ Signal input section with high gain
As in the A-75, the signal input stage is entirely configured with
low-noise discrete circuit components which can handle highpower supply voltages. This makes it possible to design thecircuit for a high gain of 22 dB, something that cannot be
achieved with OP amp ICs that have power supply voltage
constraints. As a result, the S/N ratio of the P-4500 is anastonishing 121 dB.

Signal input section

Amplification section

GAIN 22 dB

GAIN 6 dB+ INPUT+–− INPUT+– INPUT

I-V

converter–

OUTPUT

Current summing

OUTPUT

4-parallel
power
amplifier

GAIN CONTROLCIRCUIT

Trans-impedance amplifier
Buffer＋ INPUT

Current NFB
network

Buffer■ Principle of current feedback amplifier–+■ Instrumentation amplifier principle

Power amplification
stage with triple
Darlington 4-parallel
complementary
push-pull configuration

Signal input section■ Power amplification section with linear output characteristics
The power amplification stage of the P-4500 features bipolar
power transistors mounted directly to large heat sinks for highly
efficient thermal dissipation. The devices are configured as atriple Darlington 4-parallel complementary push-pull circuit thatis capable of doubling the rated output when the impedance ishalved. In other words, it achieves a fully linear power progression of 90 watts into 8 ohms, 180 watts into 4 ohms, and 360
watts into 2 ohms. It can even supply loads as low as 1 ohm
with 500 watts of power (music signals). The impressive
damping factor of 700 means that the amplifier has ample
leeway to drive any kind of loudspeaker.
Signal input section

Power amplification section(Multiple Circuit Summing)

+ B2＋

Q1

Q5+ B3－
Q2

Q9Q6

Q11

Q13

Q15

Q17Q19Q 21

Output power (W)

+ B1
Bias
stabilizer+ INPUT

300250

NFBNetworkOUTPUT

Biasstabilizer

360

200

Q3Q7Q4Q8180

100

GNDBiasstabilizer

Q10

Q12Max.
output power
Rated
output power

Q14
Q16

Q18＋

INPUT

500

145GAIN
CONTROL－399400

Biasstabilizer

GND

520

500

Triple Darlington
4-parallel complementary push-pull configuration

MCS+GAIN< –12, –6, –3 dB, MAX >

Q 20

Q 22

B390
8

4
2
1Impedance (Ohms)■ Output power characteristics

B2
Bias
stabilizer

B1DC-Servo■ Circuit diagram of amplifier section (one channel)

Bipolar power transistors

Functionality – Convenience that makes sense❶●❷●❸●●❶ Speaker output selector for two pairs of speakers●❷ Meter display characteristics selector❹●● Input selector button❸● Amplification gain selector❹Advanced Features■ 4-parallel complementary push-pull configuration
using bipolar power transistors■ Linear output characteristics (90 W / 8 ohms, 180 W /4 ohms, 360 W / 2 ohms)■ 500 W output into ultra-low impedance load of 1 ohm(music signals)■ Strong power supply with massive toroidal transformer and large 50,000 μF filtering capacitors■ Instrumentation amplifier principle■ High-gain signal input section for outstanding S/N ratio■ Dedicated power supply for signal input sectionensures stable operation■ Line and balanced input connectors■ Polarity switching for balanced input connectors■ MCS+ circuit topology further reduces noise■ Current feedback principle in amplification circuitry■ Protection circuitry using MOS-FET switches■ High damping factor of 700■ Balanced Remote Sensing■ Speaker output protection withover-current detection■ Highly responsive large peak
power meters■ Two sets of large speakerterminals■ 4-step gain control■ Support for bi-amping
and bridged mode

Large high-efficiency
toroidal power transformer

50,000 μF filtering capacitors

Input signal and protection circuit board

7 mm or larger
Max. 16 mm
MOS-FET switches

Dedicated power supply
for signal input section

Large speaker terminals

Supported spade lug
dimensions

Bridged connection example

Bi-amping connection example
Left speaker

In a bi-amped setup,the speaker units for
the LOW frequency
range and HIGH
frequency range are
driven by separate
amplifiers to prevent
unwanted interaction.

Jumper wireRIGHT

LEFT

RIGHT

LEFTLEFT＊The speakerterminals ofboth P-4500
units are notused.

P-4500 forright channel

To LEFT input

LP-4500 for
left channel

To LEFT input

LROperation mode
selector on both units
set to "BRIDGE"

Preamplifier

RIGHTLEFT＊The speakers
must have abuilt-in crossovernetwork andseparate inputs
for the LOW andHIGH range.

P-4500 for
left channel"BRIDGE"
LED lights up

Jumper wireIn bridged mode, theP-4500 becomes amonophonic amplifier
with four times higher
power output than instereo mode.

Jumper wire

RIGHT

To LEFT input

Right speaker

Right speaker

Jumper wire

Left speaker"DUAL MONO"
LED lights up

ROperation modeselector on both units
set to "DUAL MONO"

Preamplifier

Front Panel

P-4500 forright channel

To LEFT input

Rear Panel

Power meters (dB and % scale)Line input connectors

Function indicators
BRIDGE / DUAL MONO
LINE / BALANCED

Speaker output selector
A / B / A+B

Power switch

Gain selector
MAX / – 3dB– 6dB / –12dB

Meter selector
OFF / NORMAL / 3 SEC / ∞Balanced input
connectors[Pin ② (–) Pin ③ (+)]＊ Can be changed withpolarity selectorswitch

Input selector button
LINE / BALANCED

Guaranteed Specifications

0.05% with a 2-ohm load
0.02% with a 4 to 16-ohm load
0.05% with a 4 to 16-ohm load

Damping Factor

700

Input Sensitivity(with 8-ohm load)

Stereo operation

Frequency Response

At rated continuous average output: 20 - 20,000 Hz +0 –0.2 dB
At 1 watt output:
0.5 - 160,000 Hz +0 –3.0 dB

Gain

28.0 dB (GAIN selector in MAX position)(Stereo / monophonic operation)

Gain Selector

Selector position
Gain (dB)

Output Load Impedance

Stereo operation
Monophonic operation− 3 dB25− 6 dB
22−12 dB
16

2 to 16 ohms
4 to 16 ohms

＊ With music signals only, 1-ohm loads are permissible for stereo
operation and 2-ohm loads for bridged operation.

1.07 V for rated continuous average output
0.11 V for 1 watt output
Monophonic operation 2.14 V for rated continuous average output
0.11 V for 1 watt output

Input Impedance

Balanced: 40 kilohms, Line (unbalanced): 20 kilohms

S/N Ratio (A-weighted,with input shorted)

121 dB Gain selector at MAX position
126 dB Gain selector at –12 dB positionAt rated continuous average output

Power Meters

Logarithmic scale, with indication off switch–∞ to +3 dB (indication in dB and %)Hold time switchable 3 s / ∞＊During monophonic operation, both meters show the same value.

Power Requirements

120 V/220 V/230 V AC, 50/60 Hz (Voltage as indicated on rear panel)Power Consumption

62 watts
485 watts

Maximum Dimensions

WidthHeightDepthMass

29.2 kg (64.4 lbs) net
35.0 kg (77.2 lbs) in shipping carton

Intermodulation Distortion 0.01%

MAX28

AC power supply
connector ★
Balanced input
polarity selector
Operation mode selector
DUAL MONO / NORMAL /BRIDGE[Guaranteed specifications are measured according to EIA standard RS-490.]

Continuous Average Output Power (20 - 20,000 Hz) Note: Ratings marked (＊) are for music signals only.
Stereo operation
500 watts per channel into 1 ohm (＊)(both channels driven)
360 watts per channel into 2 ohms
180 watts per channel into 4 ohms
90 watts per channel into 8 ohms
Monophonic operation 1000 watts into 2 ohms (＊)(bridged connection)
720 watts into 4 ohms
360 watts into 8 ohms
Total Harmonic Distortion Stereo operation(both channels driven)
Monophonic operation(bridged connection)

Speaker terminals
A / B (2 sets)

idlein accordance with IEC 60065
465 mm (18.31")
190 mm (17.48")
427 mm (16.81")

Remarks★ This product is available in versions for 120/220/230 V AC. Make sure that the voltage shown on the rear panel matches the AC line voltage in your area.
★ The 230 V version has an Eco Mode that switches power off after 120 minutes of inactivity.
★ The shape of the plug of the supplied AC power cord depends on the voltage rating and destination country.

Supplied accessory● AC power cord

●The specifications and appearance of this product are subject to change without notice.
L1805YPRINTED IN JAPAN

850-2214-00（B1）