ONKYO Integra A-705DC

Commentary

Pre-main amplifier with 2 DC configuration that is a DC version of the equalizer amplifier and power amplifier.

The equalizer amplifier section is composed of differential amplification and interstage current mirror circuit using low-noise FET at the first stage, front three stage amplification and rear two stage differential amplification including A-class push-pull at the last stage. The high capacitance capacitors in the input side and NF loop are removed, and all capacitors in the circuit are selected from non-inductive film capacitors and high-quality audio capacitors to obtain high characteristics.
In addition, the RIAA compensation uses the same NF / CR split circuit as the A-708DC, eliminating intermodulation caused by the slew rate in the high-frequency range. As a result, high-purity sound quality is obtained without sound distortion even in the case of a pulsed signal.

The power amplifier uses the same 2-stage cascade drive and 3-stage Darlington connection DC configuration as the A-708DC.
For the DC drift of the speaker terminal voltage, which is the most important in DC amplifier, a low-noise monolithic dual FET which has the same characteristics as the first stage differential amplifier is used to construct a stable DC amplifier.

The power supply section employs a bus earth system that reduces the potential difference in the ground line across the entire circuit. It also employs a smoothing capacitor with an ESR (equivalent series resistance) of 0.01 Ω or less that maintains low impedance up to the ultra-high frequency band of 100 kHz. In addition, the power supply fluctuation rate is 0.1% or less and the ripple rejection ratio is 80 dB. From a constant voltage power supply dedicated to the pre-section, the power supply is directly connected to the equalizer and each branch by a multi-spray bus line.
This prevents interference within the same channel and between the left and right channels.

The tone control amplifier section of both Bass and Treble can be adjusted more finely by switching the turnover frequencies between two stages (with a defeat).
As for the circuit configuration, an NF variation type of differential 1-stage operational amplifier configuration is adopted to obtain accurate variation characteristics. In order to stick to the concept of DC & DC, non-inductive film capacitors and low distortion audio capacitors are used for all capacitors.

In the unlikely event that a DC voltage appears on the output, the left and right independent detectors electronically detect it and instantly disconnect the speakers to protect them. This circuit also acts as a transient killer to prevent clicks when the power is turned on.
For the speaker protection relay, a gold-plated silver contact relay is used as a 2-contact para-type to suppress the deterioration of damping caused by contact resistance. The input selector is directly embedded in the printed circuit board to prevent the deterioration of sound quality caused by the extension of the shield wire.

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 2-stage switching low filter that can switch the low cutoff of the power section to DC and 0.1 Hz.
At DC, it operates as a DC amplifier without any capacitor in the signal system of the power section and NF. At 0.1 Hz position, it is an AC power amplifier with cutoff of 0.1 Hz and can be connected to other preamplifiers with DC leakage.

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.

Model Rating

Type	Pre-main amplifier
Power Amplifier Unit
Rated Output (20 Hz to 20 kHz, Both Channel Drive)	70W + 70W (8 Ω)
Dynamic Power (1 kHz, 8 Ω)	100W+100W
Total harmonic distortion rate (20 Hz to 20 kHz)	0.02% or Less (Rated Output) 0.01% or Less (at rated 1/2 output) 0.008% 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	0.1 Hz, 6dB/oct.
Attenuator	-10dB/-20dB
S/N (IHF-A, input short)	115 dB or more
Damping factor (1 kHz, 8 Ω)	90
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, 2 mm : 2.5mV/47k 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:280mV(1kHz) 1370mV(10kHz)
S/N ratio (IHF, A-network)	Phono1, 2 mm : 82 dB or more Tuner, Aux, Tape play1, 2 : 100 dB or more
Output voltage	Pre-out (100k Ω load) : 1.5 V (rated), 14 V (maximum) Tape rec1, 2 : 150 mv (rating)
Output impedance	Pre out : 2.2k 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	+6dB(100Hz)
Filter	EQ subsonic : 15 Hz, 6dB/oct. High cut : 7 kHz, 6dB/oct.
Muting	-20dB
Input-output polarity	Equalizer amplifier : In-phase Tone amplifiers : in-phase
<Others>
Number of semiconductors used	Transistor : 56 pcs FET : 8 Diode : 26 Units
AC Output	Switched : 2 systems, total 200W Unswitched : 1 line, 200W
Pwer	100 VAC, 50Hz/60Hz
Power consumption	185W (Electrical Appliance and Material Control Law) 500W maximum power consumption
External dimensions	Width 438x Height 150x Depth 390 mm
Weight	14kg