VICTOR/JVC A-X77
¥ 110,000 (released in 1982)
Commentary
This pre-main amplifier pursues linear transmission and mounting performance.
It uses a simple 2-amp configuration, high-gain MC / MM/DC servo equalizer, and dynamic super A power amplifier for A-class operation.
The power amplifier section uses Super A, which eliminates switching distortion, crossover distortion, TIM distortion, etc. while maintaining high efficiency and high power comparable to B-class amplifiers. The addition of pure NFB, which does not damage the bare characteristics of transistors, extends the effect of NFB to the ultra-high frequency range and flattens the characteristics of the audible band.
The A-X77 adds two additional technologies to improve speaker dynamics : an isolated drive circuit and a wave collection processor.
The isolated drive circuit is inserted between the pre-drive stage and the power stage. This circuit eliminates dynamic interference between the pre-drive stage and the power stage or the speaker, and is a type of impedance conversion circuit that takes advantage of FET characteristics.
In a general power amplifier, the power stage is driven by a constant current with a pre-drive stage having a high output impedance. However, in this method, the influence of the operation fluctuation of the power stage due to the music signal and the influence of the speaker load is fed back to the pre-drive stage and large interference distortion is generated. In the power stage, the high output impedance of the pre-drive stage and the signal source impedance of the phase correction capacitor have frequency characteristics. The lower the frequency, the higher the impedance.
The impedance conversion by the isolated drive circuit can suppress these interference distortion very effectively. The pre-drive stage is free from the influence of the power stage and the speaker load, and stable operation with less distortion is possible. The power stage is driven at a constant voltage with a constant low impedance, so the output impedance is low and flat over a wide range. This improves the damping factor characteristics and enhances the driving force of the speakers.
In addition, most of the back electromotive force of the speaker is absorbed by the power stage, which prevents IIM (Interface Inter Modulation) distortion.
The Wave Collection Processor is a compensation circuit that attempts to return the power stage signal voltage waveform corrected by the Super A Bias Circuit to a complete original waveform by applying waveform manipulation with current. It performs extremely stable and wide-band distortion reduction operation without any operational disadvantages.
Together with the isolated drive circuit and newly developed Super A IC with high-speed operation and high linearity, the distortion reduction effect before applying NFB is improved by 20 to 40 dB compared to the conventional Super A. In particular, the characteristics of the important fundamental frequency band below 1 kHz are improved. This wave collection processor ensures that the linearity of the power stage is sufficient for use as a non-feedback amplifier.
The newly developed dynamic Super A dedicated IC has been adopted to improve the high-speed response and linearity while inheriting the conventional Super A operation.
The distortion factor characteristics of the equalizer amplifier section when using MC has been greatly improved.
This is due to the synergistic effect of the active broad added in the first stage and the pure NFB similar to the power amplifier section. This is achieved by increasing the open-loop gain and applying the necessary and sufficient negative feedback from low to high frequencies.
In addition to the general tandem constant voltage circuit, a shunt type constant voltage circuit is also used for the power supply circuit. While the power supply voltage is locked double, the current in the power supply line is kept constant regardless of the signal level to eliminate interference distortion between the signal path and the power supply path. This interference distortion is caused by a potential difference in the ground line. In the shunt type constant voltage circuit, the sum of the internal current and the current flowing through the load (equalizer amplifier) is always equal. Wiring close to the load eliminates the adverse effect of the potential difference caused by the resistance of the board or wiring material.
All input terminals on the rear panel are directly connected to the board, and remote switches are installed near each terminal for the phono input and speaker output to eliminate wiring and clean the signal system.
The circuit board is separated by a large heat sink in order to prevent the electromagnetic and electrostatic influence of the power amplifier, which handles large power, from affecting the equalizer amplifier.
It employs a direct power supply system in which a high-performance electrolytic capacitor is placed on the substrate of the power stage, and a thick copper plate bus bar is used to supply power to the power transistor through which a large current flows to reduce the source impedance.
The A-X77 uses a large-capacity toroidal transformer.
A short-stroke, crystal style large push switch is used as the normal switch.
In addition, a rotary switch is often used inside the sealing pocket so that the setting position can be easily understood, and operation functions are clearly distinguished.
Uses parts that emphasize sound quality such as the emitter resistance of non-resonant and non-inductive structure.
Equipped with an LED protection indicator that also serves as a volume pointer for checking the operation of the protection circuit.
It is equipped with Route 3 tape I/O, one of which is installed in the front panel sealing pocket.
Equipped with 2 types of speaker selector that can be driven in parallel.
It is equipped with a tone control circuit that suppresses unnecessary variations in the ultra-low and ultra-high ranges.
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Model Rating
| Type | Pre-main amplifier | ||
| Circuit System | |||
| Equalizer amplifier section | Pure NFB / ICL / DC servo, MC/MM equalizer amplifier with first stage EL-FET cascode bootstrap | ||
| Power amplifier section | Power Amplifier with Dynamic Super A, Pure NFB / ICL / DC First Stage Dual FET Cascode Bootstrap | ||
| Power supply part | Direct power supply (power stage) Shunt lock power supply (equalizer stage) |
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| Overall Characteristics | |||
| Effective power (Tuner, Aux, Tape → Spout) |
95W + 95W (20 hz to 20 khz, 8 Ω, 0.003% THD) 100W + 100W (1 kHz, 8 ω, THD0.0005%, By HP-IB Audio Analyze System) |
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| Total harmonic distortion factor (at effective output) |
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| Cross modulation distortion factor | 0.001% (60 Hz : 7 kHz = 4 : 1, effective output, 8 Ω, Tuner, Aux, Tape → Spout) | ||
| Switching distortion | 0 | ||
| TIM Distortion | 0(LPF fc=100kHz) | ||
| Output bandwidth | 5 Hz ~ 60 kHz (IHF, both channel operation, 8 Ω, THD0.02%, Tuner, Aux, Tape → SPOUT) | ||
| Frequency characteristic | DC ~ 300 khz + 0 -3dB (8 Ω, Tuner, Aux, Tape → Spout) | ||
| Damping factor | 150 (1 kHz, 8 Ω, Tuner, Aux, Tape → Spout) | ||
| Input Sensitivity / Impedance (1kHz) |
Phono MM : 2.5mV/47k Ω Phono MC : 200 μ V/100 Ω Tuner, Aux, Tape1/2 : 200mV/47k Ω |
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| Signal-to-noise ratio | Phono MM : 86 dB (IHF A-202 83 dB, Rec out) Phono MC : 72 dB (250 μ V input, IHF A-202 76 dB, Rec out) Tuner, Aux, Tape : 110 dB (IHF A-202 84 dB, SP out) |
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| Tone control | Bass : ± 8 dB (100 Hz) Treble : ± 8 dB (10 kHz) |
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| Subsonic filter | 18 Hz, -6dB/oct. | ||
| Loudness | + 6 dB (100 Hz), + 4 dB (10 kHz) | ||
| Muting | -20dB | ||
| Equalizer amplifier section (Phono → Rec out) | |||
| Phono maximum allowable input | Phono MM : 300 mV (1 kHz, THD0.0008%) Phono MC : 23 mV (1 kHz, 0.001% THD) |
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| RIAA deviation | 20 Hz to 20 kHz ± 0.2 dB | ||
| Total harmonic distortion factor | Phono MM : 0.002% (20 Hz to 20 kHz at 8 V output) Phono MC : 0.005% (20 Hz to 20 kHz at 8 v output) |
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| Output Voltage / Impedance | Rec out : 200mV/660 Ω | ||
| <Others> | |||
| Power outlet | Switched : two systems Unswitched-One system |
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| Pwer | 100 VAC, 50Hz/60Hz | ||
| Rated power consumption | 225W (Electrical Appliance and Material Control Law) | ||
| External dimensions | Width 435x Height 140x Depth 402 mm | ||
| Weight | 11.0kg | ||