Here is the circuit diagram of direct coupled radio. The central and core part of this circuit consists of three transistors Q1 (HEP 641), Q2 (HEP 253) and Q3 (HEP 641) as shown in the circuit diagram. In this circuit, all the three transistors are made to work as audio amplifiers. Among these transistors Q1 has got an additional function. It also acts as a diode detector. The diode detection operation is taking place at the emitter-base junction of Q1 which operates as a PN junction diode. The radio filtering stage in detection process is provided by the base-emitter capacitance of Q1. The consistency in volume and least distortion are obtained by adjusting the potentiometer R1 (47 K).

Circuit Diagram

Direct Coupled Radio Circuit

Notes

• Use a good quality PCB to assemble this particular circuit.
• This an excellent direct coupled radio circuit ideal for listening to near by stations.
• Use a center tapped ferrite antenna coil for L1 that is used AM receivers.
• Use an appropriate battery for powering this circuit since it can reduce noise in the circuit (A 3V DC battery is used here)

]]> http://amplifierlab.com/direct-coupled-radio-circuit/2010/05/16/feed 0 http://amplifierlab.com/50-watt-transistor-amplifier-circuit/2010/04/28 http://amplifierlab.com/50-watt-transistor-amplifier-circuit/2010/04/28#comments Wed, 28 Apr 2010 17:11:53 +0000 admin http://amplifierlab.com/?p=132 Circuit Description

The circuit diagram given below is 50 W transistor amplifier. This circuit is a class-B amplifier. In this circuit, seven transistors are used. Out of these transistors, six transistors acts as preamplifiers and the rest one is for driving the speaker. The transistor 2N 3055 is used here to drive the speaker. The 500 ohm pot connected to BC 107 transistor is used for adjusting maximum power level of the amplifier.

In audio applications always use power amplifiers. This circuit is a very rugged and reasonably power amplifier. The capacitors C1 (220 uF) and C2 (100-200 uF) is for controlling low and high frequencies respectively. The circuit can be powered using a 50 V DC power supply with 5A current rating. Up to 60 V can be given to the circuit. This amplifier can produce 60W rms at 50V supply on an 8 Ohm load.

Circuit Diagram

50 Watt Transistor Amplifier Circuit

Notes

• The circuit is designed such that most of the components are not critical and can be easily replaced by nearest values
• This circuit is ideal to assemble from your electronics junk box
• Volume control can be added to the circuit by connecting a 10 K POT in series to the input of the amplifier.

The circuit diagram of Cable TV amplifier has been published here. This cable TV amplifier circuit consists of two transistors Q1 and Q2 both 2SC1324 as its core part. Type number of these transistors is optional; any medium power NPN RF transistors can be used instead of it. Among these transistors Q1 is meant for amplification and gives a maximum gain of around 20 dB. Transistor Q2 functions as emitter follower. This emitter follower circuit is meant for increasing current gain.

12V DC supply is used for powering this circuit.  It is most applicable for cable TV systems that use coaxial cables of 75 ohms. This particular amplifier has less performance than other high quality cable TV amplifiers available in market since it is a simple elementary circuit.

Circuit Diagram

Cable TV Amplifier Using Transistors

Notes

• Use a Vero board to assemble components for this particular circuit.
• This amplifier works fine up to 150 MHz in cable TV systems that use 75 ohm coaxial cables.

The circuit diagram given below shows 250 mW audio amplifier. This circuit contains three transistors Q1 (BC547), Q2 (BC327), Q3 (BC337) as central components. Transistor Q1 in this circuit acts as preamplifier where as Q2 and Q3 are output pairs. Transistors Q2 and Q3 are complementary transistors. Decoupling of DC from audio source is done by the capacitor C1 (10 uF). Resistor R2 (82K) is used in this circuit to provide better stability for the amplifier. Variable resistor POT R5 (10K) is used as volume control element.

The circuit is powered using a 9V DC supply. The value of impedance of speaker K1 can be 8 ohm. In order to get the optimum output from the circuit, decouple input and output grounds properly.

Circuit diagram

Simple 250 mWAudio Amplifier

Notes

• Use a Vero board to assemble components for this circuit.
• This type of amplifiers finds applications in small radio sets and in high power amplifiers as preamplifier.

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

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

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

Circuit Schematic

Circuit Schematic

A 2 transistor tone controller circuit is illustrated below. This simple circuit is made with the help of Baxndal tone control design. A 12 Volt DC power os required for the circuit. Also note that the connection for the input and output is given in respect to the ground. Two POT’s are used. Out of these POT R5 is to bring adjustments to the bass and POT R8 is to bring adjustments to the treble. Sufficient current gain and input impedance must be provided by the circuit. For this reason, the transistor Q1 is placed as an emitter follower. Voltage amplification of the signal is provided by the second transistor. Tone is controlled by the resistor and capacitor network connected between emitter of Q1 and base of Q2. Variation of the values of these resistors and capacitors change the audio response of the system. On the frequency ranges of 10KHz to 60Hz, a maximum attenuation and boost of 10decibel is obtained. All electrolytic capacitors should have a rating of atleast 12 Volts.

Circuit Schematic