Accuphase P 7000 Brochure
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A stereo power amplifier with impressive punch: 1,000 watts into 1 ohm MCS technology in input stage improves S/N ratio, distortion ratings and other characteristics. 11 pairs of wide-band high-power transistors in parallel push-pull configuration for each channel. Power supply with massive 1.5 kVA toroidal power transformer supports linear power down to impedances as low as one ohm. Teflon PCBs with low dielectric constant and minimum loss. The P-7000 continues the distinguished design policy of the M-8000. It adds MCS technology in the input stage and many other refinements. Carefully selected top quality parts are used throughout. The design aim was to achieve very low output impedance (Note 1) and constant drive voltage (Note 2). The end result is a stereo power amplifier that provides effortless performance and impeccable sound quality. In the output stage, 11 pairs of high-power transistors with a rated collector dissipation of 150 watts are arranged in a parallel push-pull configuration for each channel. The devices are mounted to large heat sinks on both sides of the main chassis for efficient dissipation of thermal energy generated during operation. As a result, the amplifier is capable of delivering power in a linear progression towards lower load impedances: 1,000 watts into 1 ohm, 500 watts into 2 ohms, 250 watts into 4 ohms and 125 watts into 8 ohms. Speakers with very low impedances as well as speakers whose impedance fluctuates drastically can also be driven with ease. By using the P-7000 in bridged mode, it is possible to create a monophonic amplifier with even higher power. This performance is sustainedby a massive Super Ring toroidal transformer housed in a diecast enclosure with directly mounted heat sinks, and by large filtering capacitors. The transformer is rated for 1.5 kVA, and there are two capacitors of 56,000 µF each. This assures more than ample reserves and allows the amplifier to meet even the most demanding and rapidly fluctuating power requirements. The important input stage also has been given due attention. Another Accuphase innovation called MCS (Multiple Circuit Summing) helps to minimize noise. Current feedback topology combines total operation stability with excellent frequency response, while requiring only minimum amounts of negative feedback. The material used for printed circuit boards has a decisive influence not only on electrical characteristics but also on the sonic end result. The P-7000 uses Teflon boards with extremely low dielectric constant and low loss. The copper foil side of PCBs and all input and output terminals as well as all major signal carrying points are gold plated. Balanced inputs help to shut out external noise. The overall result of these measures is musical purity that leaves nothing to be desired.11-parallel push-pull power unit delivers guaranteed linear power output of 1,000 watts into 1 ohm, 500 watts into 2 ohms, 250 watts into 4 ohms and 125 watts into 8 ohms The output stage uses high-power transistors with a rated collector dissipation of 150 watts and collector current of 15 amperes. These devices boast excellent frequency response, current amplification linearity, and switching characteristics. The transistors are arranged in an 11-parallel push-pull configuration (Figure 1) for ultra-low impedance and mounted on a massive heat sink made from diecast aluminum. This assures effective heat dissipation and allows the amplifier to effortlessly handle very low impedances. Power linearity is maintained down to loads as low as 1 ohm, which demonstrates the impressive capabilities of this amplifier. MCS topology in input stage drastically improves S/N ratio, distortion, and other characteristics The input stage features Accuphase's original MCS (Multiple Circuit Summing-up) design. Three separate – B1 Q21 Q23 Q25 Q27 Q29 Q31 Q33 Q35 Q37 Q39 Q41 Q43 Q24 Q20 Q22 Q19 Q26 Q28 Q30 Q32 Q34 Q36 Q38 Q40 Q42 Q44 Q18 Q16 Q17 Q15 Q14 Q13 OUTPUT + – INPUT– INPUT+ MCS (Multiple Circuit Summing-up) Q9-12 Q1-4 Q5-8 IC2 IC1 IC3 NFB NETWORK REGULATOR REGULATOR + B1 – B2 + B2 BIAS STABILIZER CIRCUIT BIAS STABILIZER CIRCUIT BIAS STABILIZER CIRCUIT Note 1: Low amplifier output impedanceWhen 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 principleEven 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 1,050 watts. At 2 ohms, the figure is 606 watts, at 4 ohms 326 watts, and at 8 ohms 170 watts. This demonstrates the impressive performance reserves of this amplifier. Fig. 2 Output power vs. load impedance(output voltage/output current: actual measurements) * 1-ohm operation possible with music signals only Output voltage (V) Output current (A) unit amplifiers for the input signal are connected in parallel, which minimizes noise and distortion and greatly improves other performance parameters as well. This manifests itself in further improved sound quality. Current feedback circuit topology prevents phase shifts in high frequency range The P-7000 employs the original Accuphase current feedback principle. At the sensing point of the feedback loop, the impedance is kept low and current detection is performed. An impedance-converting amplifier then turns the current into a voltage to be used as the feedback signal. Since the impedance at the current feedback point (current adder in Figure 3) is very low, there is almost no phase shift. Phase compensation can be kept to a minimum, resulting in excellent transient response and Fig. 1 Circuit diagram of amplifier section (one channel)
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– Input BufferCurrent adder I-V converter Trans-impedance amplifier Amplifier Output Current NFB network + Input Fig. 3 Principle of current feedback amplifier superb sonic transparency. Minimal amounts of NFB are used for maximum effect, providing natural energy response. Figure 4 shows frequency response for different gain settings of the current feedback amplifier. The graphs demonstrate that response remains uniform over a wide range. Printed circuit boards made from Teflon with low dielectric constant and low loss The printed circuit boards for the signal-carrying circuits are made of Teflon, a glass fluorocarbon resin material. Teflon has extremely low specific inductive capacity which is desirable for fast signal transmission. The low dielectric dissipation factor results in minimal transmission losses. High-frequency characteristics and heat resistance are also excellent. For further improved sound quality, the copper foil side is gold plated. * Teflon is a registered trademark of DuPont USA. Fig. 4 Frequency response with current feedback (Response remains uniform even when gain changes) Power amplifier assembly with 11 parallel push-pull transistor pairs per channel mounted directly to large aluminum diecast heat sinks, MCS circuitry, and current feedback amplifier Robust power supply with Super Ring toroidal transformer and high filtering capacity The P-7000 features a massive toroidal power trans- former with a maximum rating of 1.5 kVA. The trans- former is housed in a non-resonant aluminum case filled with a mate- rial that transmits heat and absorbs vibrations. This completely pre- vents any ad- verse influences on other circuit parts. A toroidal transformer uses heavy-gauge cop- per wiring on a doughnut-shaped core. This results in low impedance and high effi- ciency, while al- lowing compact dimensions. Two ultra-large aluminum electrolytic capacitors rated for 56,000 µF each serve to smooth out the pulsating direct current from the rectifier, providing more than ample filtering capacity.