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Quick LM386 Question

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L3GACY

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I am trying to build the following amplifying circuit

**broken link removed**

What I was wondering is this, If I were going to amplify sound from a MIC would I connect the output to the Vin in the schematic above and my second question is if it would be possible to take the speaker out and instead put some LED's in its place to light up to sound?
Thanks In Advance
 
To Q1: Yes, but it will not work. You need a preamplifier, with a level control, for the mic to go to line-level.
To Q2: Maybe. You propably will need to rectify the output and add some electrolytics, otherwise the LEDs will just flicker (and maybe self-destruct as you are feeding them AC)
E
 
If you use 2 batteries so ground is in the middle of the 2 batteries, it will simplify the output circuit, but you are still lacking the kind of voltage gain that will bring a microphone up to that kind of power.
 
What you have there is a simple LM386 amplifier circuit with a gain of 20, the default gain for the LM386. In order to use it with a microphone, as was mentioned, you would need to add a preamplifier stage before your LM386. The preamplifier could be a simple addition of for example a TLO81 amplifier with a gain of about 10.

Now if you want to drive LEDs or lamps with sound then you are looking at a color organ (that is what they are frequently called) and some color organ circuits which can be found here. One of the circuits is a 12 volt (automotive version) which **broken link removed** The schematic for the last link uses 3 channels to filter the frequencies of the audio input. Just using a single channel and changing the filtering would simplify the circuit but is is pretty cool with three channels.

Hope that helps...
Ron
 
The gain of the LM386 is increased to 200 simply by adding a 10uf capacitor between pin 1 and pin 8 as shown in its datasheet. Then it amplifies a microphone well.
If you use an electret mic then it must be powered from a seies 10k resistor from a filtered supply voltage. For a filter I use a 1k resistor from trhe supply then a 47uF capacitor to ground.

Two LEDs an be connected back-to-back with one connected in reverse. Then the output capacitor of the LM386 circuit can feed a current-limiting resistor that is in series with the two red LEDs. The current-limiting resistor and the two LEDs replace the speaker in your schematic so one LED lights when the output goes positive and the other LED lights when the output goes negative.

The datasheet for the LM386 shows that its max output is 6V p-p when its supply is 9V. Then the peak output is only 3V which is too low to light blue, white or bright green LEDs. If your red LEDs are 2.0V then the current-limiting resistor has 1V max across it and for 25mA then its value is 1V/25mA= 40 ohms which is not a standard value. Use 39 ohms.
The brightness of the LEDs depend on the supply voltage. If a 9V battery is used then the LEDs will begin to dim immediately and and will be extremely dim when the battery voltage has dropped to 7V.

The output of the LM386 can feed up to 15 pairs of LEDs each pair with its own current-limiting resistor.
 
You do not need a preamp.
Simply add a 10uf capacitor between pin 1 and pin 8 of the LM386 to boost the gain 10 times.

A TIP31 is a big power transistor. It is never used as a preamp. Use a 2N3904 little transistor as a preamp.
 
A MPS2222A would work as a preamp if you need one. But as AG said, try it without first. Just add the recommended capacitor between pins 1 and 8.
 
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