Audio Database


Monaural power amplifier using DENON non-feedback system.

In the POA-8000, a non-feedback system that does not generate dynamic strain is adopted from the beginning, which is a complete change from the system that cancels dynamic strain.
In the non-feedback system, input signals are amplified in only one direction. First of all, a signal transmission and amplification system that does not generate transient response distortion is adopted. Distortion and noise generated in the amplification system are removed by a distortion removal circuit.
The circuit configuration of the POA-8000 is such that the main amplification system does not have a phase compensation circuit or β circuit, and the amplification stage can be reduced by half. Therefore, the main amplification system amplifies the signal in real time from input to output. Moreover, since it is one way without return, no transient distortion occurs, and excellent dynamic characteristics are obtained.

The distortion removal circuit is equipped with a voltage type at the first stage and a power type at the last stage.
This distortion removal circuit compares the input signal and output signal of the amplifier and detects all components except for the input signal as distortion of the amplifier element. Next, the distortion component extracted here is made to be opposite phase and amplified so that the distortion component on the output side and the mixing point of the main amplifier output circuit become equal. Then, the same distortion component (opposite phase) as the distortion component on the output side is added to the output side.
In this circuit, in addition to distortion, dynamic variations such as amplification, frequency characteristics, operating point drift, noise, etc., all components other than the input signal are regarded as distortion and are removed.

The basic circuit is composed mainly of 3-stage Darlington power stage, and all stages from the first stage to the last stage are composed of complimentary service A class push-pull circuit non-feedback amplifier.
The first stage consists of a complimentary service push-pull configuration of a low-noise, high-gain FET. In this configuration, a no-feedback voltage amplification is performed by a distortion removal circuit. The output is passed through a high-ft small-signal transistor-emitter-follower circuit, reduced in impedance, and sent to the predriver stage.
The pre-driver stage has a simple circuit configuration with one stage amplification by complimentary service push-pull, in this case ft130MHz, Pc1W, V.CEOFour 200 v high-voltage transistors are used in parallel to reduce the current load on each transistor and operate under optimum conditions. A high-precision metal deposition type resistor with an accuracy error of ± 1% and temperature coefficient of ± 50 ppm is used to determine the gain of this stage, ensuring highly stable characteristics.
The power stage consists of a 3-stage Darlington configuration. The fast driver stage consists of a cascode emitter follower circuit with two small signal transistors with high linearity and 400 MHz ft excellent in high-frequency characteristics. The second driver consists of a parallel push-pull circuit with four transistors. The final output stage consists of a 6-parallel push-pull circuit with 12 Pc150W high-speed power transistors.

For the circuit board of the power transistor section, glass epoxy board and oxygen-free copper board with copper foil thickness of 140 μ m with minimized circuit resistance are used, thereby reducing signal transmission loss caused by circuit hand-making at high power.

The digital display on the front front has a muting counter function that counts down from 7 to 0 when the power is turned on, and a speaker indication function of SP1orSP2 during normal operation.
In addition, it is equipped with a self-diagnosis function, which checks whether the set is operating stably, and displays errors in coded English letters (E-7 to 0) to self-diagnose error locations. The display of E-0 indicates an abnormal temperature rise, and the display of E-3 indicates an abnormal voltage at the midpoint of the main circuit. In the event of such an error or incorrect use, the output relay is instantly cut off by the detection circuit.

Equipped with peak indication type output level meter.
With dB and WATT (0 dB = 200W/8 Ω), the peak display is from -50dB to + 5 dB. When the peak level of the output exceeds the rated output even for a moment, the red LED embedded in the meter is lit for a few seconds. The peak hold function is also used.

The power supply section has a large transformer with four windings on the secondary side, and supplies high voltage and high stability current to the power section (160 v) and voltage amplifier (220 v).
The power supply section consists of a high-voltage, large-capacity electrolytic capacitor and an advisory plate that employs a 1.5 mm brass plate.

High-density cut 15 mm thick flat glass is used for the front panel and 6 mm thick smoked glass is used for the top glass cover.

The top plate is equipped with a ventilator processed by cutting extruded aluminum material treated with black alumite.

The side panel, along with an escutcheon bar, is anodized in champagne gold.

Uses a 60 mm diameter machined aluminum insulator.

Model Rating
Type Monaural power amplifier
Music output 320W (8 Ω)
Rated output 200W (8 ω, sine wave continuous, 20 Hz to 20 kHz)
Total harmonic distortion factor 0.003% or Less (8 Ω, Sine Wave Continuous, 20 Hz to 20 kHz)
Cross modulation distortion factor 0.005% or Less (60 Hz : 7 kHz = 4 : 1 at Rated Output)
Output Bandwidth (THD 0.01%) 5 Hz to 100 kHz
Input Sensitivity / Input Impedance 1V/50k Ω
Output Impedance (1 kHz) 0.1 Ω or less
Signal-to-noise ratio (IHF-A) 120 dB or more
Frequency response (at 1W output) 1 Hz ~ 200 kHz + 0 dB -3dB
Output terminal Route 2
Subsonic filter characteristics 16 Hz, 6dB/oct.
Slew rate ± 380 V / μ sec
Level Meter Characteristics
Indication system Peak value indicating type level meter
Indication range -50dB to + 5 dB (0 dB = 200W/8 Ω)
Frequency characteristic 10 Hz to 100 kHz ± 3 dB
Accessory function Rated output peak hold display
Digital Display Function
Muting display Countdown from initial value 7 to 0
Speaker display SP1, SP2
Self-diagnosis function Operation diagnosis of main circuit, distortion removal circuit and abnormal temperature rise
Power supply voltage 100 VAC, 50Hz/60Hz
Power consumption 330W (Electrical Appliance and Material Control Law)
160W (No Signal)
External dimensions Width 310x Height 188x Depth 462 mm (including height of knobs and legs)
Weight 22kg