ONKYO Integra A-927LTD

Commentary

An improved pre-main amplifier based on the Integra A-927.
It is designed freely as an amplifier that the development team wants to use by themselves, and it is realized by small production of 300 units per month.

While a general transistor amplifier uses a Darlington circuit in which emitter followers are connected in multiple stages to the power amplifier, the A-927LTD uses an inverted Darlington circuit in which collector followers are connected to the final stage.
Since the inverted Darlington is a collector follower, nonlinear distortion between the base and emitter of the power transistor does not enter the signal circuit, so nonlinear distortion can be reduced.

In addition to the conventional ground theory, the ground potential is closed loop for each stage from the signal inlet to the signal outlet, so that the potential does not change even if current flows through the load.
This eliminates interference caused by the ground loop, which previously caused masking of music information, and improves S/N and other functions.

In order to realize a non-feedback amplifier, NFB (negative feedback) is eliminated from the power amplification stage of the power amplifier, and the low distortion factor is realized by reviewing the circuit.
In addition, by reviewing the temperature compensation circuit, excellent thermal stability has been obtained, and the need for a small resistor inserted in series on the output side of the normal amplifier is eliminated, and the output impedance of the power amplifier has been reduced.

Equipped with a mid-bus presence that controls the feeling of congestion caused by the characteristics of the listening room.
This boosts and cuts the middle and low frequency range around 200 to 300 Hz, which is impossible with the conventional tone correction, and removes the uncomfortable feeling of congestion.
In addition, when the bus control is boosted, a booth is set to the middle range at the same time, which is also effective when it becomes difficult to listen.

In addition to the Source Direct Position, which bypasses the tone circuit, the Power Amp Direct Position, which can be directly input to the Power Amp from the dedicated input terminal via only the volume, is installed.

A 4-row high-grade detent volume is used so that dedicated circuits can be configured for each tone position and direct position.
In addition, assuming actual operating conditions, the rise of the attenuation curve is made gradual and the input sensitivity is revised to obtain the lowest operational feeling.

The power cable adopts the inlet method (power input connector) in accordance with IEC standard, and is 2 mm.²OFC (oxygen-free copper) cabtire cable is attached.
This allows the cable to be replaced and upgraded.

The internal structure is designed to minimize the signal path from input to output and to construct a rational power supply line. The circuit block layout is optimized as an amplifier.
Each block has a strong box-shaped structure and is connected to each other to increase the strength of the chassis as a whole. In addition, vibration analysis is focused on, and irregular ribs are provided everywhere to ensure strength and dispersion of resonance.

The power supply section is equipped with a double-core laser transformer, which is a further evolution of the previously used laser transformer.
This transformer has succeeded in reducing magnetic leakage to the limit by combining two coil cores that are continuous in the rolling direction with less magnetic resistance. Also, by cutting off part of the core, the coil shape can be made cylindrical, and even very thick copper wire can be wound without difficulty, thus greatly improving current supply capability.

The electrolytic capacitor is equipped with a blue capacitor, a custom part with strength and delicacy. The copper foil on the printed circuit board, which constitutes the main circuit, is 70 μ thick, twice the usual thickness, ensuring high quality.
In addition, WIMA film wimA and high-precision carbon resistors are used in all major areas related to sound quality to improve sound quality.

The use of a switch-type attenuator to control the balance prevents degradation of sound quality and ensures reliability.
It is also equipped with a MM/MC switching phono equalizer.

As an A-927LTD special specification, it uses a knurled volume and selector knob with which you can enjoy high-class feeling and operation feeling to reduce external vibration.
The speaker terminal is also gold-plated.

Model Rating

Type	Pre-main amplifier
Rated output (20 Hz to 20 kHz, 0.06%)	140W + 140W (4 Ω) 115W + 115W (6 Ω) 95W + 95W (8 Ω)
Dynamic Power (1 kHz)	320W + 320W (2 Ω) 200W + 200W (4 Ω) 150W + 150W (6 Ω)
Total harmonic distortion factor	0.06% (CD → SP Out, at rated output, 8 Ω, 20 Hz to 20 kHz) 0.06% (CD → SP Out, at 10W output, 8 Ω) 0.005% (Phono MM → Rec at 3 V output) 0.005% (Phono MC → Rec at 3 v output)
Cross modulation distortion factor	0.06% (at rated output, 70 Hz : 7 kHz = 4 : 1, 8 Ω)
Powerbandwidth	5 Hz ~ 70 kHz (IHF-3dB, THD 0.1%)
Damping factor	110 or More (20 Hz ~ 20 kHz, 8 Ω)
Signal-to-noise ratio	Phono MM : 87 dB (5 mV input) Phono MC : 70 dB (0.5 mV input) CD, Tuner, Line, Tape Play (Tone) : 105 dB CD, Tuner, Line, Tape Play (Source) : 117 dB
Input Sensitivity / Impedance	Phono MM : 3.0mV/47k Ω Phono MC : 300 μ V/100 Ω CD, Tuner, Line, Tape Play (Tone) : 300mV/25k Ω CD, Tuner, Line, Tape Play (Source) : 500mV/25k Ω
Phono maximum allowable input (1kHz/10kHz, 0.05%)	MM:100mV/480mV MC:10mV/48mV
Tone Control Maximum Change	Trebel (turnover : 7 kHz) : ± 10 dB (20 kHz, Volume = Center (-22dB)) Bass (turnover : 200 Hz) : + 15 dB to -6dB (20 Hz) Midbass Presence : ± 6 dB (200Hz/300Hz)
High-cut filter	6 kHz, 6dB/oct. (Treble Min)
Subsonic filter	15 Hz, 12dB/oct.
Muting	-20dB
Power supply voltage	100 VAC, 50Hz/60Hz
Power consumption	230W (Electrical Appliance and Material Control Law Standard)
External dimensions	Width 445x Height 165x Depth 436 mm
Weight	19.5kg
Attachment	OFC Cabtire power cable