Accuphase P-550
¥ 580,000 (released in April 1994)
Commentary
This is a stereo power amplifier with a low impedance output circuit and a strong power supply for accurate energy supply.
The output device is an audio power transistor with a high-output multi-emitter structure with a collector loss of 130W and a collector current of 15A. It has excellent characteristics such as frequency characteristics, linearity of current amplification factor and switching.
High power is realized by connecting this element in 10-parallel.
In addition, a power MOS FET with negative thermal characteristics is used for the drive stage, and the thermal gradient is offset from the power transistor with positive characteristics to realize stable operation.
We have developed and installed a current feedback type amplifier circuit that feeds back the output signal in the form of current.
The basic principle of this circuit is that first the impedance of the input terminal on the feedback side is lowered to detect a current, and then the current is converted to I-V (current-voltage conversion) by a transimpedance amplifier to produce an output signal.
In this circuit, since the impedance of the feedback input part is very low, phase rotation hardly occurs, and as a result, there is almost no need for phase guarantee. Therefore, it has excellent dynamic characteristics such as rise and sound quality is improved.
In this circuit, the frequency characteristics hardly change even if the gain is changed.
It can also be used as a bridge connected monaural power amplifier with a changeover switch.
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 provides high output and improved sound quality.
In addition to the usual unbalanced input, the input terminal is equipped with a balanced input terminal that is less susceptible to extraneous induction noise. The P-550 uses a method in which the signal is directly input to the non-inverted (+) and inverted (-) inputs of the input circuit.
High-purity copper is used for the part where the signal passes, and gold plate is applied on this.
The P-550 is applied to the copper foil and ground board of the printed board, the grounding board of the input section, the bus bar that supplies current to the power transistor, the input terminal, and the speaker terminal. Especially for the frequently used input terminal, the thickness is about 10 times the normal thickness to improve reliability.
A large 1200 VA toroidal transformer is used for the power supply.
The electrolytic capacitor is equipped with two large-capacity capacitors of 47,000 μ F/100WV (4.7 coulombs of charge).
Equipped with an analog type large power meter.
The output terminal is a large speaker terminal that can be used with very thick cables and banana plugs.
There are two types of speaker jacks available for bi-wiring connection.
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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 : 500 Monaural specification : 250 |
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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 (Input Short, 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 | 200W (no input) 980W (Electrical Appliance and Material Control Law) 920W (at 8 Ω load rated output) |
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| Maximum external dimensions | Width 475x Height 211x Depth 444 mm | ||||
| Weight | 33.0kg |