Description.
This jet engine sound generator circuit is based on the sound generator IC HT2844P from Holtek Semiconductors. This particular IC can make four sounds namely low speed sound of jet engine, high speed sound of jet engine, missile sound and machine gun sound. Each of these sounds can be activated by connecting the pins 12, 13, 14and 15 to ground by using the respective push button switches. Resistor R3 can be used for manually increasing or decreasing the speed.LED D1 gives a visible indication of the sound.

Circuit diagram.

Notes.

• The circuit can be powered from a 3V battery.
• Do not give more than 3.3V to the IC.
• K1 can be a 200mW/8 Ohm speaker.
• IC1 must be mounted on a holder.

Description.
Here is a very simple three transistor audio amplifier circuit that can deliver 250mW to a 8Ohm speaker. Complementary transistors BC337 and BC227 (Q3 and Q2) are used as the output pair. Transistor Q1 (BC 547) acts as the preamplifier.POT R5 can be used as a volume control. Capacitor C1 decouples the DC from the audio source. Resistor R2 ensures better stability for the amplifier.This amplifier is very suitable for application in small radio sets and as a preamplifier in high power audio amplifiers.

Circuit diagram.

Notes.

• The circuit can be powered from 9V DC.
• Assemble the circuit on a Vero board.
• K1 can be an 8 Ohm speaker.
• For better performance, properly decouple the input and output grounds.
• POT R5 can be used for adjusting volume.

Description.
Here is the circuit diagram of a 10W audio amplifier using the popular TDA2003 IC from SGS Thomson. The IC can easily deliver 10W to a 4 Ohms load at 18V DC supply voltage. The IC can be also operated from 12V and that makes it applicable in car audio systems. The useful features of TDA2003 includes short circuit protection between all pins, thermal overload protection, low harmonic distortion, low cross over distortion etc.

The circuit given here is designed as per the datasheet from the manufacturer and found to be working fine. Capacitor C7 performs the job of input DC decoupling.R2 and R3 is used to set the gain of the amplifier.C3 and R1 determines the upper cut off frequency.C6 and R4 and meant for increasing stability at high frequencies. Capacitor C5 couples the output to the speaker.

Circuit diagram with Parts list.

Notes.

• It is better to use a PCB for assembling this circuit.
• PCB layout for this circuit can be found on the datasheet of TDA2003.
• Use 18V DC for powering this circuit.
• Input ground and output ground must be properly decoupled.
• Speaker K1 can be a 4 ohm one.
• TDA2003 must be fitted with a heat sink.

Description.

Many audio mixer circuits have been published here. But I think, this one is the simplest of them. This very simple audio mixer circuit uses only one transistor. The base emitter junction of the transistor is biased by the diodes D1 and D2.The signals to be mixed are directly coupled to the base of Q1.Each input lines are current limited by using a 33K resistor. With the used component values the collector current is around 1mA.

Circuit diagram with Parts list.

Notes.

• The circuit can be assembled on a Vero board.
• The circuit can be powered from 15V DC.
• Gain of the individual channels can be adjusted by adding a 10K POT in series to the lines.

Description.
The circuit given below is of a simple audio amplifier that can deliver 12W to an 8 Ohm speaker. Op amp IC TL081 is used as the preamplifier here. Actually any opamp with matching power supply ratings can be used instead of TL081.Transistors Q1 and Q2 (TIP125 and TIP120) comprises the power amplifier stage. Output is taken from the collector junction of two transistors.

Circuit diagram.

Notes.

• The circuit can be assembled on a Vero board.
• Heat sinks are recommended for the transistors.
• A +15V/-15V dual DC power supply can be used to power the circuit.
• It is better to mount IC1 on a holder.