The basics of this amplifier is the TDA7370.

Capable of delivering 2x22W at 4Ohm from the car battery,  it's only needed to connect the stand-by at the remote output of the radio.

The schematic is in fig.1.

Figure 1 - The Car Audio Amplifier Schematic - I missed the R input ; )

This integrated circuit has four power amplifiers, two of them inverting the input signal.

Joining the inputs, we have a simple bridged amplifier.

Why the 22W?

Using some maths, we can reach that power:

In a normal amplifier, we have, at the speakers terminals (Uspk):

Uspk = 1/2Ub - UCESat = 7V - 0,3V = 6,7V  Where Ub = 14V(Battery) and UCESat the output transistors drop.

So, the RMS Voltage is:

UspkRms = Uspk / sqr2 = 6,7 / 1,414 = 4,7V

The max power in a 4 Ohm load is:

Pmax = UspkRms^2 / 4 = 5,6W

In a bridge output like this, the change in the formula is the follow:

Uspk = Ub - 2x UCESat = 14 - 2x 0,3V = 13,4V

UspkRms = Uspk / sqr2 = 13,4 / 1,414 = 9,5V

Pmax = UspkRms^2 / 4 = 22,5W

Those are the values for a gharged battery.

See?

It's simple to calculate.

Try it and give me some words from how did it work.

And here is the PCB and the component Layout (fig.2 ).

Figure 2 - The PCB and Component Layout

As you can view, the input caps are different from the schematics.

Use those of 1uF, and you can hear more powerfull low frequencies.

The two holes near the IC is for a jumper!

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