Laplace's Demon

Hi all,
I'm trying to build a microphone-driven amplifier outputing to a few low-voltage LEDs. I'm working from a very simple, 9V battery powered design using a single lm386 IC. The circuit design is similar to the "Simple LM386 Audio Amplifier" I found at http://www.techlib.com/electronics/audioamps.html#LM386. I've been experimenting trying to adapt this to drive LEDs, with the main result that I can't seem to get enough power.

As far as I can tell, this should be powerful enough to make a mic signal light up a few low voltage LEDs, but even on full gain I have to make a lot of noise into the mic to get much response.

Suggestions? Do I need more amplification for a direct mic signal?

Nigel Goodwin

An LM386 is a low gain small power amplifier, you need a mike preamp to feed it.

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CynicalMan

You could use the output of the amplifier to power a transistor which then powers the LEDs.

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audioguru

The LM386 with the capacitor between pins 1 and 8 has a voltage gain of 200.
A mic has a typical output of 10mV with normal talking so the output of the amp is 2V which will barely light an LED.
If you shout into the mic then the LED should be very bright and will need a series current-limiting resistor.

The circuit that was posted uses a dynamic mic that has a coil and magnet. Maybe an electret mic was used that won't work if it is not powered.

I think the amp should be biased so that direct-coupled LEDs can be used.
I think this circuit might work:

Attached Images

LED blinks from mic.PNG (21.6 KB, 23 views)

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