ONKYO Integra A-805
¥ 65,000 (around 1978)
Commentary
This pre-main amplifier was developed by putting new circuit know-how such as direct tone into the core of the super servo system.
The super servo system controls the DC amplifier with the built-in servo amplifier.
In addition to the NF loop of the amplifier, a servo loop is formed by combining a low-frequency amplifier and a phase inversion circuit. The frequency below the cutoff frequency (1 Hz) is completely shut out by the servo operation circuit.
As a result, not only the harmful ultra-low frequency components generated inside the amplifier but also the low-frequency counter-electromotive force that flows from the speaker to the amplifier is osae komi, and the operation of the amplifier, especially on the bias side, is very stable.
In addition, DC leakage, which generates DC voltage at the speaker output due to drift (drift of circuit operation with time), which was the fate of conventional DC amplifiers, is also suppressed to a low level.
In addition, it consists of only an equalizer amplifier and a power amplifier. The Tone Control Special uses a direct tone control method with volume control and a related loudness circuit to achieve a simple circuit structure and superior performance.
The power amplifier consists of a high-Gm monolithic dual J-FET, cascode bootstrap circuit + current mirror push-pull + constant current load Class A predriver + 3-stage Darlington single push-pull output.
As a result, we succeeded in increasing the power gain by 20 dB while keeping the distortion factor lower.
In addition, by adopting the super servo system using the servo operational amplifier, the DC drift is rather smaller than the conventional one in spite of the gain increase.
Linear switching system with very low switching distortion comparable to A-class operation is adopted for the output and transistor operating characteristics.
The linear switching method is similar to class AB using two transistors in terms of circuit structure, but by performing a special bias correction, the connecting part between the two operating characteristics is smoothly coupled, so that one operating characteristic is very linear.
Coupled with the use of high-ft power transistors, switching distortion is greatly reduced.
A bus (bus) line with low DC resistance is used for the feed line from the power supply to each block and the ground line to achieve low impedance of the power supply.
This prevents interference between the left and right channels and between the same channel.
In order to keep the bias current value of the power amplifier stable, which has a significant effect on the reproduction of the low-level signal, we have adopted a 3-point sensing bias circuit that detects the temperature difference between the three points of the pre-driver, driver, and output stage, and keeps the specified bias value constant.
When switching from large amplitude operation to pianissimo reproduction, bias fluctuation caused by temperature difference between driver and power transistor with different heat capacity is prevented, and stable low-distortion drive is achieved.
The phono terminals, which handle weak input signals, are gold-plated to keep contact resistance low. The selector switches and speaker switches are all directly connected to the terminals so that they can be switched in close proximity to the terminals to prevent noise from being picked up or interfering with each other.
The protection circuit includes a transient killer circuit unique to Integra that reduces unpleasant noise after power is turned on, and a high-speed response protection circuit that instantly cuts the output circuit and protects the speakers in the event of a DC leak.
In addition to the 4-system input selector, it is equipped with a convenient recording selector.
This lets you select a recording source independent of the source of the Input Selector during playback.
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Model Rating
| Type | Super servo type pre-main amplifier | ||||
| Rated Output (20 Hz to 20 kHz, 0.015%) | 50W + 50W (8 Ω, both channel drive) | ||||
| Total harmonic distortion factor | Phono → Rec out 2 V : 0.005% Tuner → SP. out : 0.008% (at rated 1/2 output, 20 Hz to 20 kHz) |
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| Intermodulation distortion factor (70 hz : 7 khz = 4 : 1) | 0.01% (Tuner → SP. out) | ||||
| Powerbandwidth | 10 Hz to 100 kHz (IHF-3dB, 0.2%) | ||||
| Damping factor | 70 (1 kHz, 8 Ω) | ||||
| Frequency characteristic |
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| Input Sensitivity / Impedance | Phono1, 2 : 2.9mV/47k Ω Tuner, Tape Play1, 2 : 150mV/47k Ω |
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| Phono maximum allowable input | 230 mv (1 khz, RMS 0.05%) | ||||
| Output Voltage / Impedance | Tape Rec1, 2 : 150mV/2.2k Ω | ||||
| S/N ratio (IHF A network) | Phono 1, 2 : 84 dB or more Tuner, Tape : 100 dB or more |
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| Tone control | Bass (400 Hz) : ± 8 dB at70Hz Treble (7 kHz) : ± 8 dB at20kHz |
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| Loudness | 15 Hz, 6dB/oct. | ||||
| Muting | -20dB | ||||
| Number of semiconductors used | 21C, 45 tr (4 fet), 23 di | ||||
| Pwer | 100 V, 50/60Hz | ||||
| Power consumption (Electrical Appliance and Material Control Law standard) | 90W | ||||
| AC outlet | Unswitched-1 (200W) Switched : 2 (total 200W) |
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| External dimensions | Width 435x Height 125x Depth 385 mm | ||||
| Weight | 10.5kg |