Instructables
Picture of Using LM386 as an Oscillator.
Most people know the LM386 as a mono amplifier. What may surprise some people is that the LM386 can also be easily converted into an oscillator without any other specific IC's like the common 555 timer chip.

In this Instructable, I'm going to provide a straight-forward schematic and some brief explanations as to how this will work and also some ideas as to what kind of tinkering you can do with this device.


 
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Step 1: Components List

LM386 Amplifying IC

Resistors
1k Ohm
10k Ohm
100 Ohm
100k Ohm*

*This resistor can vary between 10k Ohm and 100 k Ohm but other pots (200k or 1M) sound really nice.

Capacitors
470 microFarad Polarized (I prefer something lower than 100 microFarads and I strongly suggest using a 50 microFarad capacitor).
0.01 microFarad non-Polarized)*

*This capacitor can vary between 0.01 microFarads and 0.27 microFarads. I noticed that  using a 0.1 microFarad capacitor gets extremely close to a square wave.

Misc.
8 Ohm Speaker
9 volt Battery
9 volt Connector
Potentiometer (for volume adjustment)

Step 2: Schematic

This requires only a few components.

The LM386 has a built in feedback resistor (1350 K Ohms) to account for the likelihood that you will use a battery for your projects. By connecting Pin 1 and 8 together, you are bypassing this resistor.

Pin 7 doesn't connect anywhere.

Pin 6 connects to the 9 volt battery.

Pin 4 connects to the ground

As seen in the first picture, the Red X's indicate that there is no connection. So Pin 2 and 3 do not connect, and Pin 2 and 4 do not connect. The rest should be pretty straight forward.

The second picture is an earlier schematic. It is the same but has a few more notes. Rt and Ct indicate that these components can vary. By changing these components you can effect the Frequency being generated.

A simple equation (or so I heard) to determine the Frequency in Hertz is (2.5)/(Rt * Ct). Rt will be between 10,000 and 100,000 Ohms.

If R3 (100 Ohm) is left out or removed, you will get a loud squeal so try to avoid that.
I put one of these together it was a pretty quick build. I have never tried turning an opamp into an oscillator and this has definitely given me some ideas. I found this www.calvin.edu/~pribeiro/courses/engr332/Handouts/oscillators.pdf neat little page made by texas instruments. It outlines a circuit similar to this one and then explains how to stabilize the wave and also goes on to give instructions on how to build other oscillators with different waves shapes. This was a pretty fun toy for a while so thank you aDimWit for getting me interested and posting this.
russ_hensel5 years ago
Designers work hard to prevent thier amplifiers from becomming oscillators.  So you come along and show them how wrong thery are.  Nice work. ( just kidding ) Nice work, really 
westfw5 years ago
åww; is it really just a square wave?  I've sort of been hoping that high-power audio amplifiers might be configured as oscillators and used to drive the primaries of step-up transformers for making HV supplies, easier and perhaps more efficiently than the usual 555+power transistor setups.  After all, a 10W amplifier chip (pretty readily available, and cheap on the surplus market) ought to be good for putting 10W of power through a transformer, with a lot more protections and such than the usual circuit...

Phil B5 years ago
Using an amplifier as an oscillator should not be too surprising, since an oscillator is basically an amplifier that feeds some of its output to itself as input, setting up oscillations.  I am sure your Instructable will be helpful to anyone who has not thought of the similarity and wants to make use of it.