Amplifiers-Electronic amplifier circuits, power amplifier,audio amplifier, stereo amplifier designs

About The Circuit

Here isthe circuit diagram of a simple power megaphone circuit. All you have to look out for is whether you get the perfect power and speaker matching. For that the transistors Q1 and Q2 (HEP 230) are connected in parallel. An input voltage supply of 12 Volts is required. It can be either given from a battery supply or a DC power supply. A carbon type michrophone is more than enough for the circuit to work. It is the same component that is used in our ordinary telephone sets. A Push-to-talk (PTT) switch can be easily setup if we use an ordinary carbon type michrophone.

Any type of power transisitors can be used for this circuit. You have to only look out that the transistors used are kept on heat sinks. The volume control can be adjusted wiith the help of the POT R1, through which you will get max. volume with min. distortion. Take a look at the circuit diagram given below.

Circuit Description

About The Circuit

Though the headphones that are present in the market today are good enough, the music player may not be able to provide enough power to drive the headphone. The only way to make them produce a clear and gud sound is to amplify them. For this, a very simple circuit is enough consisting of three amplifiers. The circuit only needs a 3 Volts battery and needs to be made on a good quality Printed Circuit Board.
The transistors used for this circuit are BC 239 BC 337 and BC 327. Out of these Q1 (BC 239) acts as the pre-amplifier, while transistors Q2 (BC 337) and Q3 (BC 327) act as the driver circuit for the speaker. The performance of the circuit is increased by feeding back the emitter voltage of Q1 the base of Q1 itself through the resistance R3. You must also note down that the capacitors have a rating of 10 Volts. After the circuit is made all you have to do is ON/OFF the switch S1.

Circuit Schematic

About The Circuit

Given below is an IR audio link circuit that has been designed to transmit audio signals as far as 4 meters. The signal is passed on to the base of transistor Q1 through the resistor R4. This signal, when passing the transistor Q1 makes the transmitting diodes D1 and D2 ON.
The circuit has to be neatly designed on a PCB with a 9V PP3 battery for powering the transmitter and reciever. The IR signals that are transmitted are modullated along with the audio input.

The IR signals that are transmitted will be recieved by the photo transistor Q2. On recieving it the emitter voltage of the photo transistor changes according to the strength of the IR signal, which again depends on the sound modullated. Apart from Q2, there are also ordinary transistors Q3 and Q4 which are used to amplify the signal to drive the speaker. Capacitor C1 and Resistor R3 are connected as a filter circuit so as to avoid the interference from all the stray IR signals.

A simple 8 Ohm speaker is enough for the output. The photo transistor Q2 should be an NPN type. They can be anyone like PNZ154, PNA1605F, BPW77NA or BPW85.

Circuit Schematic