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LM386 circuit to amplify PWM output

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mdanh2002

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Hi, I am using a PIC18 to play a WAV file from the a SD card using the PWM module. Using the circuit from here https://projectproto.blogspot.sg/2010/05/pic18f-sd-wav-audio-player.html, I feed the output to the LM386 amplifier circuit following this schematics https://www.hobby-hour.com/electronics/lm386-power-audio.php

I am using the gain=20 circuit. I try with gain=200 and there is no difference.

Connecting it to an 8-ohm speaker taken from an old radio, I could hear the sound being played in the speaker. However, the volume is still not loud enough and distorted. The speaker was capable of playing very loud sound when it was still in the radio.

Is there anything I need to change to make it louder? thanks.
 
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The maximum output of the LM386 amplifier depends on its power supply voltage and the volume control setting.
With a 6V supply its output is only 0.25W which is not loud. With a 9V supply its maximum output is only 0.56W which is also not loud. With a 12V supply then its maximum output is 0.66W but it gets very hot.

To make the speaker play louder then use an amplifier with more output power (and a higher supply voltage) like the ones used in car radios.
 
I'll argue that, I've built and fixed small amps using a 9v battery and LM386 and they are capable of being "annoyingly loud" especially if driven into clipping.

If it is too quiet then you have either too small a source signal or too small a gain in the amp, or possibly the amp is faulty or wired incorrectly.

You said it sounds distorted so start with the source sound, this is probably too smal and/or distorted. You could connect that into another amp like your HiFi to test it.
 
I'll argue that, I've built and fixed small amps using a 9v battery and LM386 and they are capable of being "annoyingly loud" especially if driven into clipping.
Clipping is annoying because it is severe distortion.
A cheap little speaker has a few annoying very loud peak frequencies.
 
The source sound is from a PIC PWM output. I use that to play 8-bit PCM WAV file. I filter the output via a simple RC circuit. The source audio sounds clear when fed into a crystal earphone that I got from eBay a few years back.

The output from the PIC PWM is 5V. I use a potentiometer to reduce the output by 1/10, e.g. 0.5V, feed it into the LM386 that now runs at 9V (not 5V like before) and the sound is clearer and louder. I think my first attempt fed 5V from the PWM directly to the LM386, which causes clipping and thus the distortion.

My question is what makes the sound loud to our ears? It is just the amplitude of the signal being played?
 
Our hearing is most sensitive to 2kHz to 4kHz frequencies (a baby crying). An amplifier or speaker that peaks at those frequencies sounds like loud shrieks.

I have a cheap clock radio (I paid $1.73) and it shrieks like mad at 2kHz to 4kHz. Its output power is only about 0.3W. With a good quality speaker in a proper enclosure it does not shriek (it sounds great) and not very loud.

My home stereo produces 75 real Watts per channel and I rarely turn it up to produce that much volume.
My car radio has a total of 228 real Watts but most goes to the sub-woofer so I can feel the bass.
 
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