Accuphase PX 650 Brochure

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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 digital audio technology with Accuphase's rich expertise in the field of analog power amplifiers. The result is a six-channel digital power amplifier ideally suited for high-end home theater systems. Because six identical high-efficiency power units operating in digital 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 high efficiency, the digital circuitry keeps thermal energy generation low, making it possible to reconcile high output 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 been a recognized advantage of the digital principle for power 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 selection of components and materials are based on extensive listening tests. The aim was nothing less than to realize pure audio quality of the highest standard while making best use of the digital approach. In performance 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 and therefore operation temperatures low. A power supply rated for the same capacity in an analog amplifier would be much less powerful. The know- how accumulated by Accuphase in the analog field is also in evidence in the PX-650, as exemplified by its large toroidal transformer. By combining the advantages of the digital principle, namely high power and low current consumption, with solid engineering and sophisticated design exper tise, Accuphase has opened up a new chapter in digital audio. Balanced signal transmission with instrumenta- tion amp configuration 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 mode rejection ratio) and minimal distortion. Another significant advantage is that external noise and other external influences are vir tually shut out. The result is a drastic improvement in operation stability and reliability. INPUT NFB NETWORK GAIN CONTROL CIRCUIT DIGITAL POWER AMP. NFB NETWORK OUTPUT +INPUT + +-“ -“-“ PROTECTION CIRCUIT METER CIRCUIT INPUT SELECTORMODE SELECTOR MODE SELECTOR MODE SELECTOR OUTPUT MUTING RELAY MUTING RELAY MUTING RELAY MUTING RELAY MUTING RELAY MUTING RELAY BALANCED INPUT UNBALANCED INPUT BALANCED INPUT LEFTLEFT UNBALANCED INPUT BRIDGE C.D BRIDGE RIGHT.B A D C INPUTS SPEAKERS B RIGHT BRIDGE LEFT.A INPUT SELECTOR BALANCED INPUT UNBALANCED INPUT BALANCED INPUT UNBALANCED INPUT INPUT SELECTOR BALANCED INPUT UNBALANCED INPUT BALANCED INPUT UNBALANCED INPUT OUTPUTRIGHT OUTPUTA OUTPUTC OUTPUTD OUTPUTB GAIN CONTROL DIGITAL POWER AMP. AMP. + -“ AMP. + -“ GAIN CONTROL AMP. + -“ AMP. + -“ GAIN CONTROL AMP. + -“ AMP. + -“ GAIN CONTROL AMP. + -“ AMP. + -“ GAIN CONTROL AMP. + -“ AMP. + -“ GAIN CONTROL DIGITAL POWER AMP. DIGITAL POWER AMP. DIGITAL POWER AMP. DIGITAL POWER AMP. DIGITAL POWER AMP. AMP. + -“ AMP. + -“ NFB NFB NFB NFB NFB NFB NFB NFB NFB NFB NFB NFB nSix 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 4 ohms and 150 watts × 6 into 8 ohms. In 2-channel mode, the unit becomes even more powerful, with 250 watts × 2 into 4 ohms and 170 watts × 2 into 8 ohms. nBridged operation allows upgrade to a high-output 3-channel amplifier The two channels in all three blocks can be run in bridged mode, resulting in a full 450 watts × 3 into 6 ohms and 420 watts × 3 into 8 ohms. This represents top performance with power to spare. nPower supply features large toroidal transformer and ample filtering The toroidal power transformer of the PX-650 is rated for 820 VA, and filtering is provided by two aluminum electrolytic capacitors with ample 33,000 µF rating. nGain selector provides 6 dB increase in normal or bridged operation nMode selector allows easy implementation of bridged operation nBalanced inputs highly resistant to externally induced noise nThree 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 and illumination is also provided. nFront-panel input selector button allows easy choice of balanced and unbalanced inputs nLarge-size speaker terminals compatible with Y lugs and banana plugs PX-650 Block Diagram Signal input stage Power amp stagePower amplifier unit (2 channels) Large filtering capacitors Large toroidal power transformer Balanced/unbalanced input connectors Input selector buttonsLarge-size speaker terminals Instrumentation amplifier configuration (1 channel) Meter selector buttons

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Quantizer 4th Order Lowpass Filter Output Stage Input Stage MOS FET Driver OUTPUT INPUT Feedback Network + -“ -“ + AMP. AMP. Left-ch A-chInput + + + -“ Block diagram of digital power amplifier section (1 channel) The PX-650 features highly efficient digital power amplifiers that provide high output power with low power consumption (low heat build-up). The delta-sigma circuit principle minimizes noise in the audible frequency range. As can be seen from the illustration, the circuit comprises the input stage, quantizer, MOS FET driver stage, MOS FET output stage, and feedback network. Together, Digital power amplifier using discrete configuration these elements form a second-order delta-sigma demodulator. Many delta-sigma type digital power amplifiers use a single chip that integrates the input stage, quantizer, feedback network and other elements. In the PX-650 on the other hand, all of these circuits are built with discrete components. As a result, the noise characteristics of the PX-650 are on a par with an analog power amplifier. mContinuous average output power with six channels driven (normal operation): 150 W × 6 into 8 ohms mContinuous average output power with three channels driven (normal operation): 420 W × 3 into 8 ohms Low-pass filter choke coils High-speed diodes and drivers, ultra high-speed OP amps, and other parts Power MOS FETs Mode selector LEFT/A channel bridged connection example nIn 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 2 channels in bridged configuration, turning the 6-channel amplifier into a 3-channel component with even higher output power. Speaker Mode selector nDigital power amplifier section with power MOS FETs mounted to alumi- num heat sinks and other discrete components. Three units accommodating 2 channels each are provided, for a total of 6 channels.