Transistorized Hi-Fi Amplifier (3 Watt)

The amplifier described here is placed for the learners / Beginners / Students. The 3-Watt Output power of this amplifier is sufficient for a standard or average sized room.

The amplifier circuit described below uses six (06) silicon transistors. Since all these transistor stages are directly coupled it ensures excellent low frequency response. The use of silicon transistors provides greater stability to the amplifier and improves the high frequency response also. The transformer-less output and driver stages prevent the low and high frequency distortions associated with those transformers.

A suitable pre-amplifier described in as a separate item (Pre-amplifier for the Hi-Fi Amplifier) may be used with this amplifier in the single suitable enclosure provided that sufficient shielding should have to be incorporated in between them (i.e. Main Amplifier & Pre Amplifier).

A suitable power supply unit can be used that shall supply the required voltage for the amplifier and the pre-amplifier with rated current. For the stereo application the following items are required for the system, such as,

  • Transistorized 3-Watts High Fidelity Amplifier = 2 Units.
  • Transistorized Per Amplifier for the High Fidelity Amplifier = 2 Units.
  • Stereo Balance Meter = 1 Unit.
  • Power Supply Unit = 1 Unit

[Input: 230V AC; Output: 18V DC/2 Amp and 15V DC/0.2Amp for Pre-amplifier.]

The each output power transistors (SL100 or CL100) should have to be used with proper Heat-Sinker for individual transistors. Please keep in mind the following points and should have to be maintain properly,

  1. Dual Ganged, 10K Log Volume Control should be used for stereo Amplifier.
  2. Dual Ganged, 100K LIN BASS & TREBLE Control should be used for Stereo Amplifier.

When the amplifier wiring shall be complete, first thorough wiring +Connection checking is highly important and ensure that, there should not be any defect or wrong connection. Keep the volume control in minimum position (Fully anti-clockwise) and switch on the power supply unit. Then adjust the 10K preset (R6) in such so that, ½ of the supply voltage has to be arrived at the point marked ‘M’. When this adjustment is done, the 220 Ohms preset (R10) has to be adjusted so that the voltage across 10KPf (C6) shall be exactly 2 volts. Now the amplifier is ready to use.

Please find the schematic circuit diagram and Bill of Materials separately.

Bill of material and Circuit Schematic

Electronic Circuits – Simplified