Transistorized Hi-Fi Amplifier (15 Watt)

Now a days there are many more Integrated Circuits available in the market to make one Audio Amplifier. But, within the circuitry everything has to be taken care by the Audio Amplifier IC itself and the experimenter’s have nothing to do or learn anything on it. But, if you would like to and learn something regarding the Audio Amplifier you may go for fully transistorized audio amplifier and opportunities to have some knowledge in your mind regarding the audio amplifier.

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 15Watts 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: 36V DC/4 Amp and 18V DC/0.5Amp]

The each output power transistors (2N 3055) should have to be mounted in a separate Aluminum sheet of 2mm Thick, 70mm Height and 70mm in length for two power transistors or 140mm for four power transistors (Stereo Application). Please keep in mind the following points and should have to be maintain properly,

  1. Suitable mica insulator should have to be used for each power transistor.
  2. Dual Ganged, 10K Log Volume Control should be used for stereo Amplifier.
  3. 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. Nowthe 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