Audio Database

Image of Integra A-808
Commentary

This pre-main amplifier was developed by installing a super servo system in both the pre-amplifier and power amplifier sections and by investing new circuit know-how such as direct tone.

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.

In order to prevent the occurrence of harmful phase shift in the range of audibility, a newly developed super servo system for the A-808 is adopted, and a preamplifier which smoothly cuts the very low frequency of 2 Hz or less is adopted.
The servo operation is performed by a monolithic operational amplifier, and the signal system (coupling and NF loop) from the inlet to the output of the preamplifier does not contain any capacitor.
The Super Servo system was developed with the objective of reducing drift, eliminating coupling capacitors, and eliminating unwanted ultra-low frequency components that lead to low frequency dullness.
In addition, by adopting the direct tone method, it is a completely direct connection method in which no capacitor enters the signal path even when the tone circuit is turned on.

In the case of an ordinary DC amplifier, increasing the gain of the power amplifier inevitably increases the DC drift, and there was a limit. However, in the A-808, we have succeeded in increasing the power gain by 20 dB while keeping the distortion rate lower with the circuit configuration of high-Gm monolithic dual J-FET + cascode bootstrap circuit + current mirror push-pull + emitter follower buffer + constant current load Class A predriver + 3-stage Darlington single push-pull output.
In addition, the adoption of a super servo system using a servo operational amplifier has reduced DC drift to a lower level than before despite the gain increase.
Thus, the tone amplifier is omitted.

It employs a linear switching system with operating characteristics of the output transistor of the power amplifier section that are equivalent to those of class A operation with very little switching distortion.
The circuit configuration is similar to class AB using two transistors. A special bias circuit is used to compensate at the junction between the two operating characteristics, so that one very linear operating characteristic is finally obtained.
In addition, switching distortion is greatly reduced by using high-ft power transistors.

In order to keep the bias current value of the power amplifier stable -driver, driver and output stage in order to keep the bias current value of power amplifier stable in any case, which has a significant effect on the reproduction of low-level signal.
When switching from continuous high-amplitude operation to Pianissimo playback, bias fluctuations caused by the temperature difference between the driver and the power transistor are prevented, resulting in stable low-distortion drive.

Bus-earth (bus line) method is adopted to suppress the potential difference in the earth line over the whole circuit. Electrolytic capacitor with low ESR (equivalent series resistance) that maintains low impedance up to 100 kHz ultra-high frequency band. In addition, direct power supply system is adopted in which the equalizer and each branch are directly connected to each branch by multi-spray brine from a constant voltage power supply exclusively for pre-section.

A low distortion rate attenuator with a multi-slider enclosed in a die-cast body is continuously variable and trimless, so there is no distortion due to current concentration action, and its interlocking error is accurate to 70 dB within 0.5 dB.

Important sound quality switches, such as input selectors and speaker switches, are embedded directly in the printed circuit board or are switched near the terminals to prevent S/N and crosstalk due to interference from the routing of shield wires, and damping due to increased resistance of the speaker circuit.
In addition, the pin jack is gold-plated to prevent deterioration of sound quality caused by slight contact failure.

The protection circuit includes a transient killer circuit unique to Integra that suppresses 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 Line 5 input selector, it is equipped with a recording selector.
This allows you to choose any recording source independent of the source of the Input Selector during playback.

The load impedance of Phono1 and 2 can be switched to two levels of 47k Ω and 100k Ω to draw out the characteristic inherent in the cartridge.

Model Rating
Type Super servo type pre-main amplifier
Rated Output (20 Hz to 20 kHz, 0.015%) 70W + 70W (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)
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 90 (1 kHz, 8 Ω)
Frequency characteristic
Phono → Rec out (RIAA deviation) : ± 0.2 dB (20 Hz to 20 kHz)
Tuner → SP. out : 2 Hz ~ 100 kHz + 0 -1.5 dB
Input Sensitivity / Impedance Phono1, 2 : 2.5mV/47k Ω, 100k Ω
Tuner, AUX, Tape Play1, 2 : 150mV/47k Ω
Phono maximum allowable input 280 mv (1 khz, RMS 0.05%)
Output Voltage / Impedance Tape Rec1, 2 : 150mV/2.2k Ω
Pre Out : 1.5V/600 Ω
S/N ratio (IHF A network) Phono 1, 2 : 85 dB or more
Tuner, AUX, Tape : 100 dB or more
Tone control Bass (400 Hz) : ± 8 dB at70Hz
Treble (7 kHz) : ± 8 dB at20kHz
Loudness 15Hz/20Hz, 6dB/oct.
Muting -20dB
Number of semiconductors used 61C, 57 tr (6 FET), 33 di
Pwer 100 V, 50/60Hz
Power consumption (Electrical Appliance and Material Control Law standard) 120W
AC outlet Unswitched-1 (200W)
Switched : 2 (total 200W)
External dimensions Width 435x Height 125x Depth 385 mm
Weight 11.5kg