90Watts Amplifier Using Transistors

Using some power transistors and some other common electronic components, can be designed a high power audio amplifier capable to provide a maximum output power of 90W. This power amplifier based on transistors is capable of provide an output of 70W on a load of 8 ohms or 90W on a 4 ohms load. If the component values in parentheses are used can be connected speakers with 4 ohm impedance, in which case the amplifier maximum output power will be around 90 watts.

90Watts Amplifier Using Transistors Circuit Diagram

Amplifier Using-Transistors-Circuit Diagram
The input signal is brought to the transistor T1 and the reaction is taken on the basis of T2. Current through deferential stage is kept constant at 1 mA current source through the action of T3. The input signal for T4/T8 transistor is taken from the T1's collector in combination with current source T5 forms a control stage class A for power transistors. Current through control stage is quite small (about 7 mA) as T6 and T9 are Darlington power transistors.

Protection circuit from Fig. 2 must also be changed when using a 4 ohm load. R24 and R28 values are then 3k9, R26 and R28 are 220 ohms, and D5, D6 and R30 are all eliminated. Rectified voltage for 70 W / 8 ohms version is ± 40 V to be in load, no load, this corresponds to about ± 47 V. At 4 ohms, these values are ± 34, respectively, ± 40 V. The transformer used must provide for alternative 1A 70 W / 8 ohm (mono) and 2.2 A for version 90 W / 4 ohms.

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