Audio Database

Image of A-780
Commentary

Pre-main amplifier with super linear circuit.

Semiconductor amplification devices such as transistors have inherent non-linearity (distortion). In order to eliminate this non-linear distortion, we have adopted a super linear circuit at the first stage of the power section.
In this method, the non-linearity of the transistor and the non-linearity of the reverse mode are paired and canceled. This makes it possible to make the non-linearity of the transistor almost linear.
As a result, we succeeded in reducing NFB to about 1/1000 of the conventional one because of improved bare characteristics, and solved the unstable factors such as TIM strain caused by NFB.

In a class B amplifier, the transistor amplifier is switched in principle.
In order to resolve this switching distortion and obtain high-purity sound quality, a non-switching circuit is installed in the power amplifier.
This method uses a high-speed bias servo circuit to control the bias current according to the input signal to keep the transistor in an operating state at all times. As a result, the transistor does not switch and switching distortion is essentially 0.
We also pursue 0 crossover distortion, carefully select transistors with high pair characteristics, and set the operating point to the optimum point to achieve input / output characteristics with high linearity and close to 0 crossover distortion.

A DC servo circuit is used in the power amplifier section to cut out the unnecessary ultra-low frequencies that degrade sound quality without using a capacitor.
This DC servo realizes a circuit configuration that does not use any coupling capacitor from the AUX or Tuner input to the SP output, eliminating the coloring of sound by the coupling capacitor.

It is equipped with a line straight switch for more refined sound quality.

Equipped with MM/MC switching function that can use MC cartridge.

Equipped with a Rec Out selector, it is equipped with an indicator that shows at a glance which terminal of Rec1 or Rec2 is receiving the recording output.

Model Rating
Type Pre-main amplifier
Effective power 70W + 70W (8 Ω, 20 Hz to 20 kHz, both channel drive)
Harmonic distortion factor (20 Hz to 20 kHz) 0.009% (at effective output)
0.007% (8 Ω at 35W output)
Intermodulation distortion factor (50 hz : 7 khz = 4 : 1) 0.008% (at effective output)
0.004% (8 Ω at 35W output)
Output bandwidth 5 Hz ~ 50 kHz (IHF, both channel drive, THD 0.009%)
Output terminal Speaker : A, B
Tape Rec:150mV
Damping factor 60 (20 Hz ~ 20 kHz, 8 Ω)
Input Sensitivity / Impedance Phono MM : 2.5mV/50k Ω
Phono MC : 0.25mV/0.1k Ω
Tuner, AUX, Tape Play1, 2 : 150mV/50k Ω
Phono maximum allowable input (1 kHz) MM:200mV(THD 0.002%)
MC:20mV(THD 0.005%)
Frequency characteristic Phono MM : 20 Hz to 20 kHz ± 0.3 dB
Tuner, AUX, Tape Play : 5 hz to 200 khz + 0 to 3 db
Signal-to-noise ratio (IHF, A-network
Short circuit)
Phono MM:88dB
Phono MC:70dB
Tuner, AUX, Tape Play : 105 dB
Tone control Bass : ± 10 dB (100 Hz)
Treble : ± 10 dB (10 kHz)
Filter Low : 20 Hz, 6dB/oct.
Muting -20dB
Power supply voltage 100 VAC, 50Hz/60Hz
Power consumption (Electrical Appliance and Material Control Law) 145W
External dimensions Width 420x Height 132x Depth 423 mm
Weight 11.9kg