Thursday, May 14, 2015

Create a simple Audio Amplifier (LM386) part 2

Begin this week I created a simple Audio Amplifier with the LM386 (see previous entry). I noted that there was some noise coming from the speakers. I already had a 100uF capacitor on the breadboard to smoothen the power fluctuations. I searched the internet for solutions to further reduce the noise. I found three possible measures.
  1. Connect a 10uF to pin 7 of the LM386. In the schematics from HackaweekTV pin 7 (bypass) is not connected. On the website Learning About Electronics I found a tip to connect 10uF capacitor to this pin and ground it. Here is a link.
  2. On a another blog (Low Voltage. Mostly Harmless...) a 10nF capacitor is added to pin 6 and ground. Here is a link to this article.
  3. This is a feedback the LM386 output (pin 5) and pin 8. The feedback includes a 10k resistor and a 10nF capacitor in series. I found this tip here.
I included the three measures one after the other on my breadboard and then played some music. I found the the 1st and 3rd measure had a significant audible effect. The 2nd remedy, the 100nF capacitor added to pin 6, didn't have an audible effect. With the combined measures the noise was indeed reduced to a very acceptable level although it was not entirely gone.

For a video that demonstrates the Audio Amplifier see below.

Original 'noisy' circuit.

Improved circuit with significantly reduced noise. The 10uF capacitor between pin1 and 8 is removed. I didn't need the additional gain.

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