Accuphase P-7000, P-7921 Brochure

m Powerful 11-parallel push-pull output stage in each channel delivers

linear power into loads as low as one ohm m Input stage with MCS topology m Current feedback circuit combines excellent sound quality with total operation stability m Bridged connection mode allows upgrading to true monophonic amplifier m Massive Super Ring toroidal transformer rated for 1.5 kVA m Printed circuit boards made from Teflon material

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. P ower 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 sustained

Note 1: Low amplifier output impedance

When 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 principle

Even 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.

REGULATOR

BIAS STABILIZER CIRCUIT

REGULATOR

–

INPUT

MCS

(Multiple Circuit Summing-up)

1-4

5-8

9-12

BIAS STABILIZER

CIRCUIT

NFB

NETWORK

+ –

BIAS STABILIZER

by 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.

Output current (A)

Output voltage (V)

* 1-ohm operation possible with

music signals only

Fig. 2 Output power vs. load impedance

(output voltage/output current: actual measurements)

Q21Q23Q25Q27Q29Q31Q33Q35Q37Q39Q41Q

–

Q26Q28Q30Q32Q34Q36Q38Q40Q42Q

Fig. 1 Circuit diagram of amplifier section (one channel)

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

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

OUTPUT

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

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