105W simple power amplifier is designed for typical connection circuit for IC LM3876T company National Semiconductor and is powered by bipolar unregulated power supply voltage of ± 35 V. The opening of the switch S1 turns on mute.

Despite the simplicity and lack of adjustment elements,
-the amplifier has high performance
-ratio IMD (SMPTE 60 Hz, 7 kHz, 4:1) does not exceed 0.004%,
-typical THD 0.01%, noise level -114 dB,
-frequency response ( -3 dB) 10 Hz to 90 kHz or 20 Hz … 20 kHz ± 0,25 dB level,

So it is suitable for audio of the highest class. The gain is given by Ki = 1 + R9 / R4. The coil L1 is wound around a 2-watt (such as MLT-2) and resistor R8 has 14 turns of wire 1.3 mm in diameter. Chip to the radiator to the thermal resistance of not more than 3 ° C / W («RADIO T9» № 7-8 / 2005 sec. 14, 15 *).

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Through the use of powerful constituents (Darlington) transistor T4, T5, final stage managed to produce a sufficiently powerful amplifier of the five transistors, and three of them are shallow.

The output stage operates in B, the displacement at the bases of transistors is defined by two diodes D1, D2, which excludes the building process. The input stage, the differential pair supports a “zero” level “to break” and closes the negative feedback circuit of AC.

When you build should pay special attention to placement of elements on the board and the amplifier power supply to eliminate self-excitation of the amplifier, which can damage the output transistors connected to an amplifier and acoustic systems.

Note : Separate and adequate heatsink is needed to reduce heat in the transistor TIP142

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Features :

Setting up the amplifier is reduced to setting the quiescent current of the transistor VT9. In the gap of the collector wires included milliammeter and adjustable resistor R11 sets the current 50-70 mA. It then examines the absence of a constant voltage at the amplifier output with an accuracy of 0.1 W.

The whole setting is disabled when the load.
And do not forget to tightly attach the heat sink transistor VT4 transistors VT9. On this depends the temperature stability of the amplifier. You can, for example, hot melt glue or press the flange of the transistor VT9.

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