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How to interface a LM386N-4 to a car speaker

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AlainB

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Hi,

This is for my cell phone when I am in my car. I already made a hand free device using a small microphone and an amplified computer speaker. It is working very well. I have nothing to do to answer a call, just to say hello. My phone answer the call after 2 rings and close when the caller close his phone. All automatic.

I would like to get rid of the computer speaker. It is small but still it is anoying. So I built this amplifier. Now I hope I could find a way to plug it to one of the car speaker without destroying anything. I am sure there is more to do than just connect the output of the small amplifier to the car speaker.

Any advice?

Thanks!

Alain

PS I am already aware that there are devices commercially available that can interface a cell phone to a car radio
 

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audioguru

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If the car speaker is already driven from another amplifier or car radio then you need to switch the car speaker off the other amplifier and on to the LM386 amplifier. The switch will not be automatic. It is easier to use its own speaker.

A car's electrical supply is 14.4V sometimes. A car's speaker is usually 4 ohms. the combination will make a low output power of 0.35W but enough heat to melt the LM386.

It would be best if you use a 7809 9V voltage regulator circuit to drive the LM386 that has an 8 ohm speaker. Then the power to the speaker at clipping is 0.45W. 0.45W is not very loud in a noisy car so you might need the speaker fairly close to your ear.
 

AlainB

Member
Yes, would not be easy. Plus the ground of the small amp. is the groung of the car. I don't know if the car radio speakers are tied to the car ground.

What is the meaning of "clipping"? It is a word that you use often in your posts and I never know what it express.

Here is my actual setup in my car. The amplified speaker run at 6 volts so I used 10 diodes in serie to lower the voltage of the car to an acceptable level.

Alain
 

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audioguru

Well-Known Member
Most Helpful Member
Car speakers are usually driven with a bridged amplifier (actually two amplifiers) so that each end of the speaker is driven which doubles the voltage swing and increases the power almost 4 times. If you want to use the LM386 amplifier to drive a car speaker then both ends must be disconnected from the existing amplifier and connected to the output of the LM386 output capacitor and ground.

An amplifier can produce an output with low distortion until its output level is as high or as low it can go. Any higher or lower and the amplifier has severe clipping distortion where the output waveform is approaching a square-wave. The top and bottom of the waveform are flattened and are clipped off.
 
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