I have been forced to use only the lm358 as my op-amp choice for an electronics project. I have tried setting up a simple inverting pre-amp..using a 10k and 30k resistor. i am feeding a stable 9v to the op-amp.

It is incredibly distorted! Whatever song/sound i feed to it becomes incredibly distorted. my input signal is set as 5v.

What can I do to reduce the distortion? Btw, when nothing is playing in the sound input, there is no noise so it is clean signal to begin with..

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    \$\begingroup\$ Any chance of an oscilloscope photo of the output waveform? Also : is your input signal 5Vp-p or 5Vrms? Also, what is the gain of your amplifier? \$\endgroup\$ – Brian Drummond Mar 21 '13 at 16:15
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    \$\begingroup\$ Please share a schematic including component values used. A picture is much easier to grasp at a glance, than any verbal description, and will lead to more considered responses. \$\endgroup\$ – Anindo Ghosh Mar 21 '13 at 16:16
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    \$\begingroup\$ The LM358 isn't a great part for audio, but it should not result in incredible distortion either. You should post an image of your schematic with this type of question. You probably have incorrect biasing, but without a schematic, people can only guess. On a single supply, you have to take special steps. You need to generate a V/2 reference voltage, and shift your input signal to that DC level via a coupling capacitor. The output also has to be capacitively coupled, unless the next device expects a V/2 DC bias. \$\endgroup\$ – Kaz Mar 22 '13 at 0:08

If you're using just a single 9V power supply, then you will only get one half of the waveform you're expecting. You either need to use dual (e.g., ±9V) supplies, or you need to bias the opamp's noninverting input to half the supply voltage (4.5V) and AC-couple the audio input and output.

Also, you need to either reduce the gain or reduce the input signal level to avoid clipping. A 5V signal with a gain of -3 will (try to) produce an output signal of 15V, which is outside your supply range.

  • \$\begingroup\$ Also, input common mode voltage range is V+ − 2 Volts, output voltage range is V+ - 4 Volts, exacerbating the clipping on output. \$\endgroup\$ – Anindo Ghosh Mar 21 '13 at 16:24
  • \$\begingroup\$ How can I get -9v? I am drawing 9v from a 7809. \$\endgroup\$ – Raaj Mar 22 '13 at 3:57
  • \$\begingroup\$ In order to get an answer to that, you'll need to supply a lot more information about your current setup, such as a schematic diagram of your power supply and amplifier circuits. \$\endgroup\$ – Dave Tweed Mar 22 '13 at 4:03
  • \$\begingroup\$ yeah..this was the correct answer. Did a 9V to the opamp supply and the signal was about 5V (which can be slowly amplified). Sound was clean \$\endgroup\$ – Raaj Aug 13 '13 at 19:03

Try using another dual op amp. If its still as bad, it's your topology that's the problem as someone said before, the input of single rail op amps needs a 1/2 vcc voltage fed through a 100k resistor applied to both sides of the op amp.. Either inverting or non... A And b.


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