I am trying to build an audio system . I have a speaker which is rated 10 W and 8 Ohms . I am using a circuit from datasheet of TDA2040 with a pre-amplifier circuit with the microphone . when I connected it on a breadboard it seem to work fine at low volume but when I raise the volume the speaker starts to beep and sounds becomes unclear.Microphone Pre-amp circuit

TDA2040 circuit

instead of variable 100Kohm ~ 1Mohm variable pot I am using a 100Kohm fixed resistor.I am using a variable pot between the the two circuits to control the volume.I am powered the TDA2040 circuit with 12V 1A adapter and pass the same source through a regulator to the Pre-amp circuit.Are there possible reasons makes the speaker beeps at high volume ?

  • \$\begingroup\$ What do you mean by "beep"? Have you ruled out the possibility of your speaker being the problem, rather than the amplifier? \$\endgroup\$
    – Hearth
    Feb 10, 2019 at 16:56
  • \$\begingroup\$ Also, could this be phase inversion? I'm not familiar with the TDA2040 but many op amps, especially old designs like the TDA2040 appears to be, exhibit phase inversion when overdriven, causing severe distortion of the signal. \$\endgroup\$
    – Hearth
    Feb 10, 2019 at 16:59
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    \$\begingroup\$ speaker beeps at high volume That's an oscillation. The TDA2040 is difficult to get stable, I know from experience. It is because is has a very high gain. What might happen is that the changes in supply current taken by the TDA2040 somehow get into your signal path. The TDA2040 might need its own connection (wire) to the power supply. Your LM358 circuit is also supply sensitive, improve that by placing a 10 uF cap in parallel with R4 (that's R4 in the LM358 circuit!!!). You could also lower the gain a bit by increasing the value of R4 (680 ohm) in the TDA2040 circuit. \$\endgroup\$ Feb 10, 2019 at 16:59
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    \$\begingroup\$ Also, your output capacitor is waaay too small for 10 watts. Pay attention to your second schematic. And a 9-volt supply, especially a 9-volt battery, will never produce 10 watts. So you'll fairly quickly get into clipping and other issues. \$\endgroup\$ Feb 10, 2019 at 17:16
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    \$\begingroup\$ @RamyNosir This looks more like a matter of cut and paste and little actual thinking about even the most basic details, let alone the myriad subtler details that need to be considered. For example, you need more than 3 amps, peak to peak, into your speaker if you want to get near 10 watts. This will mean perhaps 25 volts peak to peak and perhaps 5 volts of headroom beyond that, or more. But you mention using a 12 volt, 1 amp power supply. Maybe you don't need or want as much as 10 watts? I can't tell. Yet you selected a 25 watt amplifier? Perhaps you can tell us more about your real goals? \$\endgroup\$
    – jonk
    Feb 10, 2019 at 20:42

1 Answer 1


After changing the power supply and make it up to 18V 2A there was no change . However when I changed the value of R4 in TDA2040 to 2 Kohms The noise was relatively reduced. under same Power supply voltage .


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