I am just trying to build a mixer circuit to change stereo to mono using a summing circuit for a project.


simulate this circuit – Schematic created using CircuitLab

As shown by the drawing, I am using the lm386n-1 op-amp as an audio amplifier, with supply voltages of 9V and GND. When I apply an audio input, the output waveform is clipped at -40 mV for the negative component of the input waveform. There is no clipping on the positive component. Why is the output clipped to -40 mV when a negative voltage is applied?

The audio inputs are in mV range so I don't think the output will exceed the supply voltage.


closed as unclear what you're asking by uint128_t, PeterJ, brhans, Daniel Grillo, Bimpelrekkie Mar 22 '16 at 8:04

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    \$\begingroup\$ First off, the LM386 is a power amplifier, not an op-amp. And with no negative supply, why would you expect the output to go negative. \$\endgroup\$ – uint128_t Mar 18 '16 at 19:53
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    \$\begingroup\$ Using this circuit shows that you have neither read the datasheet, or done any research whatsoever. -1 and voting to close. \$\endgroup\$ – Matt Young Mar 18 '16 at 20:04
  • \$\begingroup\$ See my answer to [a similar question] (electronics.stackexchange.com/questions/223441/…) earlier today. In this case you are feeding a signal alternating above and below zero volts. Your amplifier can't do that on a single supply. \$\endgroup\$ – Transistor Mar 18 '16 at 20:16
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    \$\begingroup\$ That's why all the example circuits you ignored in the datasheet use coupling capacitors. \$\endgroup\$ – Brian Drummond Mar 18 '16 at 20:57

Most amplifiers can vary their output between the two supply voltages they run from. The output can't go above the positive supply voltage. It can't go below the negative supply voltage. (Many amps can't quite reach the supply voltages either, but that's not relevant here). Since you have connected the negative supply of your amp to ground, the output cannot go below ground.

Note that the lm386 is designed as a "single supply" amp. That means the lower supply voltage will (almost) always be ground.

  • \$\begingroup\$ That's not an op-amp, and it isn't designed for two supply voltages. \$\endgroup\$ – JRE Mar 22 '16 at 15:45

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