I am using an LM386 to generate white noise. The circuit also has a second 386 for an on-board audio amplifier. Both chips are powered by the same 9V battery.

The audio amp won't pass the white noise signal and I can't figure out why, is there an impedance-matching issue? I have tried different value capacitors to buffer between the two ICs, resistors, resistors-to-ground, and an op-amp with 1:1 ratio.

When I turn the noise generator on and off, I can hear like a DC 'pop' on the speaker, but I can't hear the noise. When I tap the signal at C3 (between the two 386's) and plug that into a commercial amp, I can hear the signal fine. There's just something about that second amp that won't pass the white noise.

schematic https://www.circuitlab.com/circuit/g85pxv/white-noise-and-lm386-amp/

  • 1
    How are you mixing the signals together - do you have a circuit to show us? – Andy aka Apr 19 '13 at 18:03
  • 1
    @pinhead, a schematic of your actual circuit would be very helpful. It would be much easier to read a complete schematic than to try to work out what is in it from your comments and text. – The Photon Apr 19 '13 at 19:05
  • 1
    where is the blocking cap between the two LM386? – markrages Apr 19 '13 at 20:08
  • 1
    Listen dude, you've been repeatedly asked to show the full circuit and you still haven't. This is getting very frustrating and until we see what your circuit is I really don't think anyone is going to be able to answer this. FULL circuit please – Andy aka Apr 19 '13 at 20:51
  • 1
    @MattYoung There are other sound sources being mixed at the input of the audio amp (square waves generated with a 40106 Schmitt Trigger Oscillator). The other sound sources pass through the amp fine to the speaker. With those components removed (until the circuit is as drawn above), I still have the problem. – pinhead Apr 19 '13 at 21:41

Pin 3 (final stage) might need a resistor to ground - try 1kohm. All the application circuits I've seen do have a lowish value.

Also I have reservations about it working correctly without a low impedance on the 1st stage speaker output (after the capacitor) so try a resistor on pin 3 (2nd stage) that is more like 10 ohms.

protected by W5VO Apr 20 '13 at 1:39

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.