Test a general-purpose LM358 amplifier circuit.
I found this Op-Amp Audio Amplifier circuit and decided to test it out.
My intention was to house it as a general purpose amplifier for the workbench. However after testing the performance I think it’s perhaps not such a useful circuit.
Two issues I seeing:
- the R8=1MΩ provides ridiculous gain, so most signals over 50mV or so slam to upper/lower output limits (effectively converting any input signal to a square wave)
- the push-pull output stage cannot deliver much power, and the maximum peak-peak range with a 5V supply is about 3.2V, and the output wave is offset down ~1V from the midpoint of this range, leading to early low-side clipping
Here are some scope traces:
- CH1 is the output
- CH2 is the input
With a 200mV 1kHz input signal, the output is severely clipped:
Replacing R8 with 31kΩ, I can eliminate clipping:
Variations from the Original Circuit
Some variations in my build based on parts availability:
- 2N4401 replaced with 2N3904
- 2N4403 replaced with 2N3906
- 1N914S replaced with 1N4148
- 3.3µF C2 replaced with 1µF
Laid out on a protoboard: