Build directions

This design is very easy to build. You should start with all low SMD parts. Solder in the electrolytic caps at last. For this solder job I recommend a good pair of tweezers. I use a type especially made for SMD. With this pair of tweezers I get a very good grip. You must also have a soldering iron with a small tip but.

If you don't want the input filter just short R2 with tin or a small wire.

Start with all low SMD parts

  1. Resistors
    Capacitors, not the electrolytic ones
  2. Then continue with the high electrolytic caps
  3. Wires

Check the finished amp

Apply voltage and check the output voltage. Measure the DC voltage at the output. It should be the specified offset voltage, a couple of millivolts.

If the output offset voltage is a bit high you may need to adjust it.

Click on the pictures to get a larger view.

What you need for offset trim is a potentiometer and a resistor to inject current to the input. At the pictures you can see to different alternatives (choose one of them, the one at the right picture is the best). 10k pot + 100 k plus a 2.2 MOhms which you connect to the input. It depends if you shall connect the 100 k to plus or minus 15 volts. This is dependent of the sign if the base current of the input. Most likely you have more current gain in the NPN transistor, therefore the potentiometer must be connected to plus 15 volts.

Measure the quiescent current.

The whole amp is ready.

Good luck and happy listening.