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Project Notes

#241 General Purpose 358 Amp

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:



The Schematic


Laid out on a protoboard:




Credits and References

About LEAP#241 OpAmpAudio
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This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects, usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.