This project uses an LM3915 bar-graph IC driving two sets of ten LEDs for a 30dB range. The circuit is unique because it has an additional range of 20dB provided by an automatic gain control to allow it to be very sensitive to low sound levels but it increases its range 20dB for loud sounds.
Sound Level Indicator – [Link]
Simple and low cost. The optimal supply voltage is around 50V, but this amp work from 30 to 60V. The maximal input voltage is around 0.8 – 1V. As you can see, in this design the components have a big tolerance, so you can build it almost of the components, which you find at home. The and transistors can be any NPN type power transistor, but do not use Darlington types… The output power is around 60W.
2N3055 Power Amplifier - [Link]
This is a very simple, low cost, Hi-Fi quality power amplifier. You can build it 5 ways, like it’s shown in the table (from 20 W to 80 W RMS).
Motorola Hi-Fi power amplifier – [Link]
This is a simple bridge amplifier based on TDA7240A. This circuit is designed for car audio system, but you may use this circuit for your small home audio application…
20W Bridge Amplifier using TDA7240A – [Link]
This project is a 20W audio amplifier based on LM1875 IC from National Semiconductors. With a 25V dual power supply LM1875 can deliver 20W of audio power into a 4 ohm speaker.
20W audio amplifier using LM1875 - [Link]
This circuit is a MOSFET Audio Amplifier rated at 25 Watt. It is high quality and simple design. There is also a kit available on the link below.
25 Watt MosFet Audio Amplifier - [Link]
This project shows how to build a Vacuum Tube Preamplifier based on ECC802S (12AU7 / ECC82) Vacuum Tube. This one is high voltage so it is geared towards more advanced builders. Follow construction details on the link below.
DIY Vacuum Tube Preamplifier Project - [Link]
Ruby is a battery-powered amplifier and it is an “enhanced” version of the Little Gem. This amplifier is based on LM386 chip and has an input buffer that is feeding the inverting input. The input buffer helps to retain treble detail going into the 386 chip. It is powered from a single 9V battery. Check schematic and construction details on the link below.
Ruby : A battery-powered amplifier – [Link]
The LM386 IC is a low voltage power amplifier. The gain is set to 20 but can be changed from 20 to 200 using external components. The basic setup is really simple using only a few components as shown on the schematic above.
Audio Power Amplifier using LM386 - [Link]