How to Build a Car Audio Amplifier

By Simon Foden

You need a dedicated amplifier to power large car speakers.
i car speaker image by Sean Gladwell from

If you like high-fidelity audio in your car, the factory-installed system might not be sufficient. You'll have to modify your system to include an amplifier if you want to power large speakers, and you can save money by building it yourself. An amplifier in a vehicle functions the same as one in a home system. It converts an audio signal from the receiver or player and turns it into electrical current to power the speakers.

Source your parts. There are two ways to obtain them: Use a self-assembly audio amplifier kit and car audio wiring system or salvage the parts individually from various appliances. The latter approach is cheaper, but takes longer and there is no guarantee that the parts will be compatible. Self-assembly audio amp kits have pre-drilled parts.

Inspect your parts. Use a magnifying lens to check the resistors, fuses and capacitors. If you are using pre-owned components, look out for signs of oxidation; brown discoloration near or on the connector legs is a sign of this. Discard and replace any components that you suspect might be oxidized or corroded.

Read the schematic. If you are using a kit, it will include a schematic. If you are salvaging your parts, you can view audio amplifier schematics online. The Schematics for Free website has an archive of schematics from various manufacturers.

Load the turret board. Follow the schematic for reference. Start with the resistors, then capacitors, potentiometers, amp-chips, then fuses. Start with the highest-value component of each type. Push each board-mounted component into the turret board. The connectors will protrude through the other side. Once full, place the board face down and solder the connectors to the metal strip on the board base.

Load the chassis-mount components. Fit the power supply, power and output transformers and RCA jacks into the pre-drilled slots on the chassis enclosure. A car audio amplifier connects to the car battery; therefore, use an IEC power-supply socket with a 100-amp fuse.

Mount the board. Solder the board into the base of the chassis.

Solder the chassis-mounted parts to the circuit board.

Cut a piece of wire for each terminal on each component. Trim a half-inch of insulation from both ends. Solder one end to the output terminal on the component. The number of terminals depends on the make and model of each component. Typically, IEC power supplies have a negative and a positive output terminal. Potentiometers typically have one output terminal and two ground terminals. Wire all positive connections with red wire to the relevant positive eyelet on the board. Wire all negative connections with black wire to the negative eyelet. Solder black wire between ground terminals and the chassis ground screw.