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How do I bridge two lm386 OP Amp ICs ?

My idea is to make a electret microphone amplifier powerful enough to drive a speaker. I was using the lm386 because I was familiar with it´s chracteristics and already had a schematic to make a 200 gain amplifier. However, when I tried to use this one to amplify a microphone signal it ended up not providing enough power to drive a 8 ohm speaker (you had to stand right next to the speaker in order to hear something and even when doing so the microphone seemed to only pick up loud noises) despite the results of a similar test made with headphones proved to be more than successful.
Seeing this, I assumed that connecting another lm386 amplifier to the output of the first one would improve the results. Boy i was wrong.
After hearing the unearthly noises that came out of my proyect I decided to do some research on the internet and came up with the bridge and parallel configurations. Nevertheless, i did not find any proper schematics involving two lm386.

It would be of great help if anyone could hand in a  schematic or tip on how could I continue from ths point.


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MrB12 (author) 4 months ago

Update: I have changed my power supply from my 7.2 v battery to a 9 v one because that´s what I had available. However, when I was testing if everything was working, a loud noise came out of the speaker after turning the volume up, making it impossible to hear the microphone signal which was slightly audible with low volume.

How could I solve this problem?

Downunder35m4 months ago

I would suggest to use a 16 or 32 Ohm speaker.
8Ohm is putting a lot of strain on things for no good reason.
After all you want to amplify a signal from the mic but not create speaker horn - or am I wrong? ;)
Depending on your power source it might just break in once the speaker is sucking enough juice out of it.
Worst example here would be a 9V battery....

Actually for low voltage applications, It's common to see 4 ohm drivers. An 8 ohm speaker can only pull peaks of 600mA @5V. Powered from a 7.2V battery, assuming that's single ended (w/ a floating ground at Vcc/2 the speaker will only see 3.6V peaks, and draw about 45mA. Not much at all.

MrB12 (author) 4 months ago

Thank you all for your answers. I will firstly try to increase the input voltage since I´m currently using a 7.2 v rechargable battery. If need more help I´ll post another comment/question.

-max-4 months ago

The 386 can drive 1W, which is enough to make it plenty loud. Afrotechmods recently did a video on this chip, you may want to check it out.

You may not be using enough voltage to drive the speaker. If you want to drive 1W of power into the speaker, you probably need like 10V to drive the speaker, and at least 480uF series capacitor to remove DC bias.

+1. Plenty of "oomph" in a 386