m Digital power amplifier with totally separate six-channel configurationm Output power 200 watts × 6 into 4 ohms, 150 watts × 6 into 8 ohms
m Bridged operation further increases output to 450 watts × 3 into 6 ohms
and 420 watts × 3 into 8 ohms m Instrumentation amplifier principle for fullybalanced signal paths m Large 820 VA toroidal transformer m Balanced inputs
m Three large analog power meters m Large-size speaker terminals

Six-channel digital power amplifier – Six totally separate power units
with identical performance. Discrete delta-sigma type digital power
units ensure extremely low noise. Large 820 VA toroidal transformer
and large filtering capacitors provide ample muscle: 200 watts × 6
into 4 ohms or 150 watts × 6 into 8 ohms. Bridged mode allows
upgrade to 3-channel amplifier with 420 watts × 3 into 8 ohms.
The PX-650 represents a successful blend of digitalaudio technology with Accuphase's rich expertisein the field of analog power amplifiers. The result isa six-channel digital power amplifier ideally suitedfor high-end home theater systems. Because six
identical high-efficiency power units operating indigital mode are used, all channels provide the same
excellent sound quality. The PX-650 can drive any
kind of speaker with ease and authority, creating a
spacious surround sound stage with pinpoint imaging
and impressive dynamics. Thanks to its highefficiency, the digital circuitry keeps thermal energy
generation low, making it possible to reconcile highoutput power levels with compact unit dimensions.
This is especially welcome in multi-channel systems
for home theater applications.
The capability for high power and small size has beena recognized advantage of the digital principle forpower amplifiers, but performance and sound quality
related problems had to be overcome before
adoption in a high-end audio product was possible.
The PX-650 represents a breakthrough in the field.
It is the result of a highly focused step-by-step
approach to identify and solve these pertinent
problems. Circuit topology as well as the selectionof components and materials are based on extensive
listening tests. The aim was nothing less than torealize pure audio quality of the highest standard
while making best use of the digital approach. Inperformance as well as in sound quality, the PX-650
is a case in point. The digital switching principle
boasts extremely low internal losses. The power
supply is not called upon to provide superfluous
energy, which in turn keeps power consumption andtherefore operation temperatures low. A power
supply rated for the same capacity in an analog
amplifier would be much less powerful. The knowhow accumulated by Accuphase in the analog field
is also in evidence in the PX-650, as exemplified byits large toroidal transformer. By combining theadvantages of the digital principle, namely highpower and low current consumption, with solidengineering and sophisticated design expertise,
Accuphase has opened up a new chapter in digitalaudio.

n Six digital power amp units with identical performance allow
configuring a superb 5.1 channel surround system using a single
component
With all six channels operating, the PX-650 delivers 200 watts × 6 into 4ohms and 150 watts × 6 into 8 ohms. In 2-channel mode, the unit becomeseven more powerful, with 250 watts × 2 into 4 ohms and 170 watts × 2 into
8 ohms.
n Bridged operation allows upgrade to a high-output 3-channel
amplifier
The two channels in all three blocks can be run in bridgedmode, resulting in a full 450 watts × 3 into 6 ohms and 420watts × 3 into 8 ohms. This represents top performancewith power to spare.

Power amplifier unit (2 channels)n Power supply features large toroidal transformer andample filtering
The toroidal power transformer of the PX-650 is rated for820 VA, and filtering is provided by two aluminum electrolytic
capacitors with ample 33,000 µF rating.
n Gain selector provides 6 dB increase in normal orbridged operation

Large toroidal power transformer

Large filtering capacitorsn Mode selector allows easy implementation ofbridged operationn Balanced inputs highly resistant to externallyinduced noisen Three analog power meters with direct reading scale
A meter selector button allows use of the meters for all six
channels. On/off switching for meter operation andillumination is also provided.
n Front-panel input selector button allows easy choiceof balanced and unbalanced inputs

Balanced/unbalanced input connectors

Meter selector buttons

n Large-size speaker terminals compatible withY lugs and banana plugs
Large-size speaker terminals

Input selector buttons

+AMP.
–

BALANCED
INPUT

NFB
GAIN
CONTROLLEFTNFBUNBALANCEDINPUTDIGITAL
POWER
AMP.

MUTINGRELAY

LEFT
OUTPUT–

INPUT
SELECTOR

AMP.

MODE
SELECTOR+
BRIDGE
LEFT.A+AMP.
–BALANCED
INPUT

NFB
GAIN
CONTROLAUNBALANCED
INPUT

NFB

DIGITAL
POWER
AMP.

MUTINGRELAY

AOUTPUT–AMP.

Balanced signal transmission with instrumentation amp configuration++AMP.

The PX-650 features the highly advanced"instrumentation amplifier" principle whereby all
signal paths from the inputs to the power amp stage
are fully balanced. Ideal signal transmission
conditions result in excellent CMRR (common moderejection ratio) and minimal distortion. Anothersignificant advantage is that external noise and otherexternal influences are virtually shut out. The result
is a drastic improvement in operation stability andreliability.

–BALANCED
INPUT

NFB
GAIN
CONTROLCNFBUNBALANCEDINPUTPower amp stage

MODE
SELECTOR+BRIDGE
C.D
AMP.
–

BALANCED
INPUT

NFB
GAIN
CONTROLDUNBALANCED
INPUT

NFB

MUTINGRELAYDOUTPUT

AMP.
++
AMP.
–
NFB
GAIN
CONTROL

RIGHT

–

NFB

DIGITAL
POWER
AMP.

MUTINGRELAYRIGHT
OUTPUT–

INPUT
SELECTOR

AMP.

MODE
SELECTOR+
BRIDGERIGHT.B+

NFB
NETWORKAMP.

DIGITAL
POWER
AMP.

–

BALANCEDINPUTOUTPUTUNBALANCED
INPUT

NFB

DIGITAL
POWER
AMP.

MUTINGRELAY

BOUTPUT–AMP.
+–+

Instrumentation amplifier configuration (1 channel)

NFB
GAIN
CONTROL

B

NFB
NETWORK– INPUTDIGITALPOWER
AMP.

–+GAIN CONTROLCIRCUITSPEAKERS+UNBALANCEDINPUT+ INPUTCOUTPUTAMP.

BALANCED
INPUT

Signal input stage

MUTINGRELAY–INPUT
SELECTOR

INPUTSDIGITALPOWER
AMP.

METER CIRCUIT

PX-650 Block Diagram

PROTECTION CIRCUITDigital power amplifier using discrete configuration
The PX-650 features highly efficient digital power amplifiers that provide high output

these elements form a second-order delta-sigma demodulator. Many delta-sigmapower with low power consumption (low heat build-up). The delta-sigma circuit principle

type digital power amplifiers use a single chip that integrates the input stage, quantizer,

minimizes noise in the audible frequency range.

feedback network and other elements. In the PX-650 on the other hand, all of theseAs can be seen from the illustration, the circuit comprises the input stage, quantizer,circuits are built with discrete components. As a result, the noise characteristics ofMOS FET driver stage, MOS FET output stage, and feedback network. Together,the PX-650 are on a par with an analog power amplifier.

Block diagram of digital
power amplifier section(1 channel)

INPUT

Input
Stage

m Continuous average output power withsix channels driven (normal operation):
150 W × 6 into 8 ohms
m Continuous average output power withthree channels driven (normaloperation): 420 W × 3 into 8 ohms

OutputStage

Quantizer

MOS FET
Driver

4th Order
Lowpass
Filter

Low-pass filter choke coils

OUTPUT

Feedback
NetworkPower MOS FETsn Digital power amplifier section withpower MOS FETs mounted to aluminum heat sinks and other discrete
components. Three units
accommodating
2 channels eachare provided, for a
total of 6 channels.

High-speed diodes and drivers, ultra
high-speed OP amps, and other partsn In the output stage, the PX-650 uses power
MOS FET devices with high withstand voltage
and low on-resistance, allowing single-ended
circuit topology similar to an analog power
amplifier. This also makes it possible to use 2channels in bridged configuration, turning the6-channel amplifier into a 3-channel
component with even higher output power.
Mode selector–

Left-ch
Input

AMP.

++

Speaker+Mode selector

–
A-ch

AMP.

+–+

LEFT/A channel bridged
connection example

Connection examples for various system configurations with PX-650✻ Use speakers with rated impedance between 4 and 16 ohms.
✻ In bridged mode, use speakers with rated impedance between 6 and 16 ohms.

Surround sound playback

2-channel (stereo) playback
A Stereo playback using 2 channels ofthe PX-650
B Stereo playback with bridged
configuration, using 4 channels of thePX-650

LeftRight

Preamplifier

Connect the VX-700 or A/V amplifier pre out or the 6-channel control center CX-260 orsimilar to the PX-650.

PX-650

Stereo playback in bi-amped configuration

A 6-channel (5.1 channel) surroundplayback
B 4-channel playback

Front speaker(LEFT)

This refers to playback of a down-mixed
signal without using a center speaker or
subwoofer. Because two unused channels
are available, bridged operation for front
left and right is possible.

Front speaker(RIGHT)
Centerspeaker (C)In a bi-amped system, the LOW and HIGH
range speaker units are driven by
separate full-range amplifiers, which can
result in better sound quality.

Left

RightPreamplifier✻ A preamplifier with two outputs is required. A speaker
type with built-in network but separate LOW/HIGH
inputs is required.
✻ If bridged mode is used for the LOW range, all 6channels are used.

LOW

LOW

HIGH

HIGH
PX-650Multi-amp or subwoofer system

DVD player
Subwoofer(D)Using the six power amplifier channels effectively, a high-quality multi-amp system
can be configured with a single PX-650.
✻ The connection requires a multichannel divider (DF-45 or similar).
✻ Use a passive subwoofer (without built-in power amplifier)VX-700

Left speakersystem

A 3-way multi-amplifier system
Left surroundspeaker (A)Right surroundspeaker (B)PX-650✻ Use a passivesubwoofer (withoutbuilt-in power amplifier)Connect up to six speakers

Preamplifier

Right speakersystemB 2-way multi-amplifier system
C Stereo + subwoofer system
DF-45

D 2-way multi-amplifier + subwoofersystemn Example of a 3-way multi-amp systemn Front panel

PX-650

Guaranteed Specifications[Guaranteed specifications are measured according to EIA standard RS-490.]m Continuous Average Output Power (20 - 20,000 Hz)
Note: Load ratings marked ✻ apply only to operation with music signals.

4Ω6Ω8Ω4Ω
6Ω8Ω
4Ω
6Ω
8Ω
6Ω( )
8Ω
6Ω( )
8Ω

6ch

3ch

2chn Rear panelm LEFT, RIGHT, A, B, C, D channels are entirely separate and have identical specifications
m LEFT/A, C/D, RIGHT/B channels can be selectively bridged
BridgedBridged3ch(Bridge)
2ch(Bridge)

B

RIGHTDCA

LEFT

ChannelChannelChannelChannelChannelCD200W
200W
170W170W
150W
150W
240W
–
200W
–
160W
–––––––
450W
420W
––

LEFT
A
200W
200W
170W
170W
150W
150W
240W
–
200W
–
160W
–
250W
–
210W
–
170W
–
450W
420W
530W
450W

m The output value in the "3ch", "2ch", and "2ch (Bridge)" columns applies to any channel.

BridgedChannel

B
RIGHT
200W
200W
170W
170W
150W
150W
240W
–
200W
–
160W
–
250W
–
210W
–
170W
–
450W
420W
530W
450W

m Total Harmonic Distortion (at half power)
Six-channel operation
0.1 %, with 4 to 8-ohm load
Three-channel operation
0.1 %, with 6 to 16-ohm load (bridged mode)m Intermodulation Distortion

0.003 %m Frequency Response (into 4 ohms, for all channels)
At rated output:
20 - 20,000 Hz +0, –0.2 dB
At 1 watt output:
2 - 80,000 Hz +0, –3.0 dB
m Gain (for all channels)

28.0 dB (Normal/Bridge)
34.0 dB (Normal +6 dB/Bridge +6 dB)

m Output Load ImpedanceSix-channel operation:
Three-channel operation:

4 to 16 ohms
6 to 16 ohms (bridged mode)

Note: In bridged mode, 6-ohm loads are permissible for music signals only.
m Damping Factor

Normal mode
Bridged mode

150 (50 Hz)
175 (50 Hz)

m Input Sensitivity (with 8-ohm load) Six-channel operation★
A Meter display indicators
B Power meters (switchable for 3 channels)
C Bridging indicators
D Meter on/off and illumination button
E METER selector: L, C, R/A, D, B
F Power switch
G Input selector buttons(BALANCED/UNBALANCED)
H 6-channel speaker outputs

I Mode selectors
Normal/bridged/gain setting for
LEFT/A, C/D, RIGHT/B
J Input connectors
6-channel balanced inputs
a Ground b Inverted (–)
c Non-inverted (+)
6-channel unbalanced inputs
K AC power supply connector★

m Input Impedance

Three-channel operation(bridged mode)

1.38 V
0.11 V
2.31 V
0.11 Vfor rated output
for 1 watt output
for rated output
for 1 watt output

Balanced:
Unbalanced:

40 kilohms
20 kilohms

m Signal-to-Noise Ratio

100 dB at rated output (A-weighted, input shorted)m Output Level Meters– 40 dB to +3 dB (dB/% indication)
Logarithmic scale, with OFF switch

m Power Requirements

AC120 V/230 V, 50/60 Hz (Voltage as indicated on rear panel)m Power Consumption

48 watts idle
275 watts in accordance with IEC 60065

m Dimensions

Width 465 mm (18-5/16")
Height 180 mm (7-1/16")
Depth 418 mm (16-7/16")

m Mass25.8 kg (56.9 lbs) net
31.0 kg (68.3 lbs) in shipping carton

Remarks★ This product is available in versions for 120/230 V AC. Make sure that the voltage shown on the rear panel matches the AC line voltage in your area.
★ The shape of the AC inlet and plug of the supplied power cord depends on the voltage rating and destination country.

n Supplied accessories: AC power cord

• Specifications and design subject to change without notice for improvements.

http://www.accuphase.com/J0512Y

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