Op-Amp w/Diode
This is not a real op-amp. It's intended for making discrete versions of IC distortion units. Note: If the positive input is grounded, as in an inverting amplifier, the circuit needs a 1uF or greater cap across the lower 10k resistor. Otherwise it should be left out.

The output is class-A and won't drive heavy loads. This circuit was designed because the diode trick has to be done within the op-amp itself, therefore it was made as simple as possible. Use it in the distortion sections of your favorite overdrive/distortion unit.

Get out the breadboard and adjust the 6.8k resistor until the output collector is near 4.5 volts.