Accuphase P-700
¥ 780,000 (released in December 1995)
Commentary
This is a stereo power amplifier developed by combining AccuPhase's audio technology with the highest-grade element that has been thoroughly examined for higher sound quality.
The output stage employs a high-power multi-emitter audio power transistor with a collector loss of 130W and a collector current of 15A. This element has excellent characteristics such as frequency characteristics, current amplification linearity, switching, etc. It is composed of 12-parallel push-pull and mounted on a large heat sink made of aluminum die-cast for effective heat dissipation.
In the drive stage, a power MOS FET with negative characteristics of current against heat generation is adopted, and thermal gradient is offset from power transistor with positive characteristics to realize stable operation.
The amplifier circuit employs a current feedback type amplifier circuit that feeds back the output signal in the form of a current.
The basic principle of this circuit is that a current is detected by first reducing the input impedance of the feedback side. The current is then converted to I-V (current-voltage) by a transimpedance amplifier to produce an output signal. In this circuit, phase rotation is less likely to occur because the impedance of the feedback input part is low, and phase compensation is hardly necessary.
Therefore, various characteristics can be greatly improved with a small amount of NFB, and it is possible to obtain a natural energy response in terms of sound quality as well as excellent dynamic characteristics such as start-up.
Equipped with a changeover switch, it can also be used as a bridge connected monaural power amplifier.
Bridge connection is a method in which two channel amplifiers are supplied with signals of the same voltage and opposite phases, and speakers are connected to the output terminals of both amplifiers. This enables high power supply.
The Load Impedance switch allows driving to a low impedance of 2 Ω. When the switch is in Low mode, the voltage on the secondary side of the transformer can be reduced and the output can be limited (350Wx2 at 2 Ω).
It also has a safety feature that monitors the temperature of the heat sink and automatically switches to Low mode when the temperature reaches a certain level. In this case, when the temperature of the heat sink decreases, it returns to the normal state.
The gain does not change even when the mode is switched, so the volume level does not change.
In addition to the usual unbalanced input, the input terminal is equipped with a balanced input that is less susceptible to extraneous induction noise.
The balanced input of the P-700 uses a configuration in which the signal is directly injected into the non-inverting (+) and inverting (-) inputs of the input circuit.
The power supply section uses a large toroidal type with a large power capacity of approximately 1,500 VA.
The P-700 uses a super-ring type toroidal transformer in particular. Since the cross section of the iron core is close to a circle, the coil can be wound close to a circle and adhesion is good, and leakage flux, groaning and vibration at the time of load are reduced.
In addition, by reducing the cross-sectional area of the iron core and increasing the weight ratio of the copper wire, iron loss and inrush current are also reduced.
The electrolytic capacitor is equipped with 2 units of 40,000 μ F/120WV.
High-purity copper is used for the part where the signal passes, and in addition, it is plated with gold.
The P-700 features improved sound quality, including the copper foil side of the printed board, an earth plate through which a large ripple current flows, a bus bar that supplies current to power transistors, input terminals, and speaker terminals.
Equipped with an analog power meter that can directly read a wide power range by logarithmic compression.
It also has a switch to turn on/off the meter operation and lighting.
Equipped with a super-large speaker terminal that can be used with a banana plug.
This terminal is made by cutting out solid brass into a gold plate, and a mold cap for insulation is placed on it.
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Model Rating
| Type | Stereo power amplifier | ||||
| Continuous Average Output (20 Hz to 20 kHz) |
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| Total harmonic distortion factor |
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| IM distortion factor | 0.003% | ||||
| Frequency characteristic | 20 Hz ~ 20 kHz + 0 -0.2 dB (at rated continuous average output) 0.5 Hz ~ 160 kHz + 0 -3.0 dB (at 1W Output) |
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| Gain | 28.0 dB (both stereo and monaural specifications) | ||||
| Load impedance | Stereo specification : 2 Ω ~ 16 Ω Monaural specification : 4 Ω ~ 16 Ω |
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| Damping factor | Stereo specification : 400 Monaural specification : 200 |
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| Input sensitivity (8 Ω load) |
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| Input impedance | Unbalanced input : 20k Ω Balance Input : 40k Ω |
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| S/N (A correction) | 123 dB (at input short circuit, rated continuous average output) | ||||
| Output meter | Logarithmic compression type -50dB to + 3 db and output direct-reading scale |
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| Pwer | 100 VAC, 50Hz/60Hz | ||||
| Power consumption | 210W (no input) 1200W (Electrical Appliance and Material Control Law) 1230W (at 8 Ω load rated output) |
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| Maximum external dimensions | Width 475x Height 238x Depth 540 mm | ||||
| Weight | 42.0kg |