HITACHI Lo-D HMA-9500mkII Power Amplifier

Description

A stereo power amplifier that inherits the know-how gained from the HMA-9500 and uses a non-cutoff A circuit.
Power MOS FETs have a high amplification factor (transconductance) of 3 orders of magnitude or more compared to conventional small signal MOS FETs, have good linearity, and have excellent high frequency characteristics of 1 digit or more compared to bipolar transistors.
In addition, the switching speed is high due to the operating principle. More resistant to electrical destruction than bipolar transistors. Since the input characteristics are enhancement characteristics, the bias circuit is simpler than FETs with depletion characteristics. When used in a complementary circuit as an audio amplifier, it has many features such as being able to build a push-pull amplifier with less distortion than an amplifier using a bipolar transistor.
The non-cutoff A circuit which can greatly reduce a switching distortion is adopted.
This circuit does not fix the bias voltage of an output stage, and by automatically controlling according to an input signal, the output transistor is always ON and the cutoff is prevented.
The circuit configuration consists of a differential amplifier in the first stage and a differential amplifier with a current mirror circuit as the load in the second stage. The mutual conductance of the power MOS FET is large, the linearity and frequency characteristics are good, the power gain is large, and the complementary characteristics of the N channel and P channel are well aligned, so it is as simple as 3 stages including the power amplifier. It has a circuit configuration.
The power transformer is provided independently on the left and right, and not only the rectification smoothing circuit of the power amplification stage but also the stabilized power supply for small signals are made independent on the left and right, and the transient crosstalk via the power supply is eliminated.
Moreover, the large-capacity capacitor with a good high frequency characteristic is adopted as a smoothing capacitor.
Since the power MOS FET has a negative current-temperature characteristic at the time of a large current, even if the current tries to concentrate on a part of the semiconductor substrate, the current decreases when the temperature of that part rises. Therefore, there is no risk of current concentration or thermal runaway that causes secondary destruction such as bipolar transistors.
Furthermore, the left and right sides of the heat sink made of aluminum die-cast, which has an excellent heat dissipation effect, are used independently, and a bare chassis structure is adopted.
The input terminals are gold-plated.
The DC amplifier composition is adopted.
Model: Stereo power amplifier
Circuit method: 2-stage differential amplification Pre-stage direct connection Power MOS FET Pure Complementary OCL circuit
Built-in non-cutoff A circuit
Effective output (both channels drive): 120W + 120W (8Ω, 5Hz to 20kHz)
Total harmonic distortion:
(8Ω, rated output): 0.01% (5Hz-100kHz)
0.005% (5Hz-20kHz)
0.002% (1kHz, rated output)
Intermodulation distortion factor: 0.003% (8Ω at rated output)
Frequency characteristic:
DC: DC-100kHz +0 -0.5dB
DC ~ 300kHz +0 -1dB
Low cut: 3Hz-300kHz +0 -1dB
Input sensitivity / impedance: 1V / 50kΩ
SN ratio (input short): 120dB
Damping factor: 70
Rated power consumption: 360W (Electrical Appliance and Material Control Law)
External dimensions: Width 435 x Height 192 x Depth 410 mm
Weight: 29kg
Power supply voltage
:
AC100V, 50Hz / 60Hz
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