ONKYO Integra A-817EX
¥ 79,800 (released in 1988)
Commentary
Stereo pre-main amplifier with optical drive system.
The power amplifier section uses a newly developed optical drive system.
In this method, the reference current of the first stage differential amplifier circuit is obtained from a photovoltaic element that generates a constant voltage when light is irradiated. By obtaining a reference current with higher accuracy than that of the conventional method, highly accurate V to I conversion is performed.
In order to prevent magnetic flux from entering the amplifier circuit from the power supply part, the power supply block is separated from other circuits, and the top cover is made independent to realize a complete two box structure.
Each of the two top covers is firmly attached with 6 φ 4 mm screws to suppress vibration caused by sound pressure.
Furthermore, the amplifier block is divided into a large enclosure-type heat sink, a current amplifier stage closed loop with a barrier, and a driver voltage amplifier stage, each of which is shielded to prevent electromagnetic coupling.
A large heat sink is used to surround the power stage in order to cut off interference from the power stage handling large current to the voltage amplification stage processing small signals.
In this enclosure-type heat sink, the radiation fins are arranged independently on the left and right, and the fins are designed to have unequal lengths to disperse resonance. In addition, a vibration control structure using a special damper is also added.
The power supply section uses a large power transformer with a capacity of 250 VA and a weight of 5 kg, a twin-roll Chemicon with low impedance, and a high-speed diode with a recovery time of 1/10 of the conventional one.
The Twin-Roll Chemi-Con has a structure in which two pairs of positive and negative foils are wound in one case. By connecting two pairs of foils reinforced to 2.5 times the thickness of the negative foils in parallel inside, the internal resistance is reduced to 1/3 of the impedance.
In addition, a rubber type absorber is used for the transformer part to provide damping measures.
In order to protect the amplifier circuit from external vibration, a special alloy hexabalance base is adopted. The chassis frame is directly mounted on this base to suppress external vibration such as floor vibration and sound pressure.
In addition, the Hexa Balance Base adopts a 6-point grounding structure, and by adding two legs closer to the power supply section, we have succeeded in balancing the overall weight.
In order to transmit all music signals with high purity, it is equipped with a source direct switch that sends the source directly to the power amplifier via a dedicated volume.
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Model Rating
| Type | Pre-main amplifier |
| Rated output (20 Hz to 20 kHz CD → sp out, both channels driven) |
120W + 120W (6 Ω) 105W + 105W (8 Ω) |
| Dynamic Power | 295W + 295W (2 Ω) 235W + 235W (4 Ω) 190W + 190W (6 Ω) |
| Total harmonic distortion rate (20 Hz to 20 kHz) | CD → sp out : 0.004% (8 Ω at rated output) Phono MM → rec out : 0.003% (at 3 v output) Phono MC → rec out : 0.015% (at 3 v output) |
| Intermodulation distortion factor (20 Hz to 20 kHz) | CD → sp out : 0.004% (at rated output) |
| Powerbandwidth | 5 Hz to 100 kHz (IHF-3dB, THD 0.2%, 8 Ω) |
| Damping factor (1 kHz, 8 Ω) | 100 |
| Frequency characteristic | Phono → rec out (RIAA deviation) : 20 Hz to 20 kHz ± 0.2 dB CD → sp out : 2 Hz to 100 kHz + 0 -3dB |
| Input Sensitivity / Impedance | Phono MM : 2.5mV/47k Ω Phono MC : 160 μ V/220 Ω CD, etc. : 150mV/47k Ω |
| Phono maximum allowable input (1kHz/10kHz, 0.005%) |
MM:210mV/1000mV MC:13mV/65mV |
| Rated output voltage / impedance | Tape rec, others : 150mV/560 Ω Pre out : 1V/600 Ω |
| Video input / output | VCR, Others : 1Vp-p/75 Ω |
| SN ratio (IHF-A filter input short) | Phono MM : 94 dB (5 mV input) Phono MC : 75 dB (0.5 mV input) CD, other : 107 dB |
| Tone Control Maximum Change (Volume -16dB) |
Bass : + / - 10 dB Treble : + / - 8 dB Contrabass : + 10 dB (muting off), + 20 dB (muting on) |
| Muting (under Volume Center) | -15dB |
| Power supply voltage | 100 VAC, 50Hz/60Hz |
| Power consumption (Electrical Appliance and Material Control Law) | 215W |
| AC outlet | Switched : 1 system, 100W Unswitched : 2 lines, 100W total |
| External dimensions | Width 435x Height 168x Depth 392 mm |
| Weight | 20.3kg |