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Topic: how to amplify Simple SD Audio? (Read 1 time) previous topic - next topic

hart

I managed to get this library (http://arduino.cc/forum/index.php/topic,112745.0.html) working on an Arduino Uno (R3) in under 30 minutes and was very happy to hear the audio coming out of my speaker - however, when I tried connecting an LM386N-3 based 1W amplifier (http://ebookbrowse.com/n48fl-pdf-d393297795) with a set gain of 50 (adjustable input attentuation via POT) to the output pin (using the recommendations in the docs (.h) for powered speakers), all I got was beeping noises rather than audio?

I tried another amp kit based on NE5532 chip and got the same result - which means I'm doing something very wrong :-)

Any advice appreciated!


Grumpy_Mike

It is hard to see what you did because all that link did was to download a dmg file to my Mac, and I am not about to run random untrusted stuff on my machine.

However, it is well known that these amplifiers require large power supply decoupling capacitors to stop them hooting. I suspect that you have not got a big enough capacitor here.

DuaneB

Read this
http://rcarduino.blogspot.com/2012/04/servo-problems-with-arduino-part-1.html
then watch this
http://rcarduino.blogspot.com/2012/04/servo-problems-part-2-demonstration.html

Rcarduino.blogspot.com

Tuttut

Hi,
the audio signal level coming from a pwm pin is vey high - often too high - for direct connection to an amplifier. So try the following:

PWM out --> capacitor 100nF to 10uF --> potentiometer to ground with slider to input to amplifier

Poti value between 1k to 100k should work. If no poti availible, use resistor divider for ratio about 1:100 to 1:1000


hart

Thanks for the suggestions all - I'll give it a try after xmas is over - the PDF from the link above for the LM386 circuit is attached.


Grumpy_Mike

@Tuttut - The input to the amplifier shows it already going through a pot so thee is no worry about the input being too high.

Coupling the arduino output through a capacitor is however a good idea.
The circuit shown only a 220uF capacitor across the supply, I would recommend at least a 1000uF.

Make sure the ground of this circuit is connected to the ground of the arduino.

DuaneB

Hi,

Double check that your capacitors are the right way around as well

Duane B

rcarduino.blogspot.com

Read this
http://rcarduino.blogspot.com/2012/04/servo-problems-with-arduino-part-1.html
then watch this
http://rcarduino.blogspot.com/2012/04/servo-problems-part-2-demonstration.html

Rcarduino.blogspot.com

hart

Looks like the problem was a dry joint on one of the caps in the amp circuit - it's working perfectly now :-)  I also reduced the input signal to the amp by running the audio output pin through a cap, resistor and then tying it to ground via another resistor.  works a treat now.  Thanks for the help folks!

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