ONKYO Integra A-708DC
¥ 108,000 (around 1977)
Commentary
Pre-main amplifier with 2 DC configuration that is a DC version of the equalizer amplifier and power amplifier.
The RIAA compensation in the equalizer amplifier section is divided into two types in terms of frequency, high and low. The NF type is used for low boost and the CR type is used for high cut. The CR attenuation is used to compensate for high frequencies, so there is no problem with slew rate or blocking, and intermodulation is reduced.
In addition, since these two time-constant circuits handle each band, an excellent accuracy of ± 0.2 dB RIAA deviation between 10 and 100 kHz is achieved.
The power amplifier section is DC configuration, low-noise monolithic dual FET is used for the first stage differential amplifier, 2-stage cascade drive system and 3-stage Darlington connection output stage are adopted to obtain good linearity and stable characteristics over the whole range, and the DC drift of the speaker terminal voltage is within ± 20 mv at ± 30 ℃ relative to the temperature of 20 ℃.
Also, switching distortion, which is common in B-class amplifiers, is minimized by driving a power transistor with a high transition frequency fT with a constant voltage drive.
The power supply uses a bus-earth (bus line) system that reduces the potential difference in the ground line across the entire circuit.
In addition, a smoothing capacitor of E. S. R. (equivalent series resistance) 0.01 Ω or less that maintains low impedance up to the ultra-high frequency band of 100 kHz, and a constant voltage circuit for the pre-section that is independent of the left and right channels with a voltage fluctuation rate of 0.1% or less and ripple rejection ratio of 80 dB. The D. L. C direct-coupled power supply system that has been cultivated in the past Integra has been adopted. This system prevents mutual interference between the circuits in the front and rear stages of the same channel and between the left and right channels, and also prevents mutual interference between the circuits in the front and rear stages of the same channel and between the left and right channels. It is combined with a DC & DC circuit to improve the rise characteristics of the low-frequency range and secure a sufficient peak power.
For tone control, fine frequency adjustment is possible by two step switching of turnover frequency (with defeat).
The circuit configuration is a 4-chip configuration (actually 5 chips) using a pair transistor in the first stage. In addition to eliminating the large capacitor of the emitter, a low-distortion film capacitor is also used for the small capacitor (1 μ F and 10 μ F) of the NF loop.
This makes it possible to control the sound with less degradation even when the tone is turned on.
We have further developed the concept of DC & DC, in which high-capacity Chemicon was removed from the NF system of equalizer and power amplifier. We have removed highly strained Chemicon from all signal systems as well as interstage coupling. We have also carefully selected low-distortion non-inductive film capacitors for small-capacity capacitors.
As a protective circuit, it is equipped with a speaker relay that detects the DC voltage contained in the output and the overcurrent of the power transistor in a purely electronic manner and disconnects the speaker in the event of an emergency. This relay also functions as a transient killer that prevents a click when the power is turned on. Its operation can be confirmed by an indicator on the front panel.
The DC voltage detection section is independent on the left and right sides, so that it can operate even when the DC polarity is different on the left and right sides. The overcurrent detection circuit can quickly disconnect the speaker when the load is short-circuited or when the circuit is overloaded due to a low impedance load.
The relay uses a gold-plated silver contact type with low contact resistance.
Considering the use of MC cartridge, low noise MC head amplifier of A-class push-pull configuration is mounted.
The switches that are important for sound quality, such as input selectors and speaker switches, are embedded directly in the printed circuit board or are switched in close proximity to the terminals to reduce S/N and crosstalk caused by interference from the routing of shield wires, as well as damping caused by an increase in the resistance of the speaker circuit.
The power section is a DC amplifier, but the cut-off frequency of the lower range can be changed to DC-0. 1Hz-30Hz with the Cut-off FREQ switch.
In the DC position, there is no capacitor in the signal path or NF loop from the input to the output of the power section. The 0.1 Hz position is used as an AC amplifier with a cutoff of 0.1 Hz, and the 30 Hz position is used as a normal subsonic filter.
In order to bring out the performance of the cartridge, the load impedance of the MM cartridge can be switched to 3 stages with Phono1.
In order to keep the bias current value of the power amplifier stable, a newly developed autotracking bias method is adopted.
This is a 3-point sensing bias circuit for the pre-driver, driver and output stage. It prevents bias fluctuations caused by the temperature difference between the driver and the power transistor when switching from continuous large-amplitude operation to pianissimo reproduction, and enables stable low-distortion drive.
Equipped with a power amplifier gain 3-stage switching function, the gain can be changed over 3 stages of 0 db, -10dB and -20dB.
The s / N ratio for practical use can be improved by lowering the gain of the power section when low volume.
The Phono input terminal is gold-plated.
The volume is equipped with a low strain rate attenuator with a multi-slider enclosed in a tight die-cast body.
Since it is continuously variable and trimless, there is no distortion due to current concentration action, and the interlocking error is within 0.5 dB up to 70 dB.
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Model Rating
| Type | Pre-main amplifier |
| Power Amplifier Unit | |
| Rated Output (20 Hz to 20 kHz, Both Channel Drive) | 80W + 80W (8 Ω) |
| Dynamic Power (1 kHz, 8 Ω) | 115W+115W |
| Total harmonic distortion rate (20 Hz to 20 kHz) | 0.02% or Less (Rated Output) 0.01% or Less (at rated 1/2 output) 0.007% or Less (at 1W output) |
| Intermodulation distortion factor (70 hz : 7 khz = 4 : 1) | 0.001% or Less (at Rated Output) |
| Power Band Wiz (IHF-3dB, THD0.2%) | 5 Hz (Measurement Limit) ~ 100 kHz |
| Frequency characteristic | DC ~ 250 khz + 0 -1.5 db |
| Filter | 0.1Hz/30Hz, 6dB/oct. |
| Attenuator | -10dB/-20dB |
| S/N (IHF-A, input short) | 115 dB or more |
| Damping factor (1 kHz, 8 Ω) | 110 |
| Input Sensitivity / Impedance | Main in : 1.5V/100k Ω |
| Load impedance | 4 Ω ~ 16 Ω |
| Gain | 24.6dB |
| Input-output polarity | Inphase |
| Transient killer operating time | After Power On : 6 seconds Power after turning off : 0.2 seconds |
| Output terminal | SP-A, B, A + B, Headphone |
| Preamplifier Section | |
| Input Sensitivity / Impedance | Phono1 mm : 2.5mV/100k Ω, 47k Ω, 33k Ω Phono2 mm : 2.5mV/47k Ω Phono3 mc : 100 μ V/20 Ω Tuner, Aux, Tape play1, 2 : 150mV/50k Ω |
| Total harmonic distortion factor (Phono → Pre out) | 0.005% or Less (20 Hz to 20 kHz at 6 V Output) |
| Intermodulation distortion factor (70 hz : 7 khz = 4 : 1) | 0.007% or Less (at 1.5 v Output) |
| Frequency characteristic | Phono (RIAA deviation) : 20 Hz to 20 kHz ± 0.2 dB Tuner, Aux, Tape play1, 2 : 5 Hz to 100 kHz + 0 to 1.5 dB |
| Phono maximum allowable input (RMS, THD0.05%) | MM:300mV(1kHz) 1460mV(10kHz) MC:13mV(1kHz) 47mV(10kHz) |
| S/N ratio (IHF, A-network) | Phono1, 2 mm : 82 dB or more Phono3 mc : 68 dB or more Tuner, Aux, Tape play1, 2 : 100 dB or more |
| Output voltage | Pre-out (100k Ω load) : 1.5 V (rated), 18 V (maximum) Tape rec1, 2 : 150 mv (rating) |
| Output impedance | Pre out : 56 Ω Tape rec1, 2 (Phono) : 3.4k Ω |
| Tone Control (2 db Step Type) | Bass : ± 10 dB (100 Hz, turnover 400 Hz) Treble : ± 10 dB (10 kHz, 2 kHz turnover) |
| Turnover frequency | Bass : 400 Hz, 125 Hz, defeat Treble : 2 kHz, 8 kHz, defeat |
| Loudness | +3dB/+6dB(100Hz) |
| Filter | EQ subsonic : 15 Hz, 6dB/oct. High cut : 7kHz/15kHz, 6dB/oct. |
| Muting | -20dB |
| Input-output polarity | MC amplifier : reverse phase Equalizer amplifier : In-phase Tone amplifiers : in-phase |
| <Others> | |
| Number of semiconductors used | Transistor : 71 FET : 10 Diode : 45 pcs |
| AC Output | Switched : 2 systems, total 200W Unswitched : 1 line, 200W |
| Pwer | 100 VAC, 50Hz/60Hz |
| Power consumption | 210W (Electrical Appliance and Material Control Law) 580W maximum power consumption |
| External dimensions | Width 438x Height 150x Depth 390 mm |
| Weight | 15kg |