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  • Author Author: mrchunckuee
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LM386 Audio Amplifier

mrchunckuee

Greetings! My first post on Element, is a small audio amplifier using LM386 integrated.

 

For the design has been based on the one proposed in the datasheet (Gain = 200), some components and filters are added to the feed inlet (VALIM = 12V), the circuit used is this:

AMPLIFICADOR%2BDE%2BAUDIO%2BCON%2BLM386.png

Here more photos of the PCB:

buttom pcb

3%2BAMPLIFICADOR%2BDE%2BAUDIO%2BCON%2BLM386.jpg

The final PCB with all componences looks like this:

4%2BAMPLIFICADOR%2BDE%2BAUDIO%2BCON%2BLM386.jpg

Here one video of the circuit in action (video in spanish):

 

 

See more projects or info in my blog (in spanish)

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  • What is the bandwidth for the amplifier?

     

    DAB

  • in reply to DAB

    Page 4 of the datasheet has a graph of Voltage Gain vs Frequency. That shows about 40kHz for the IC itself with a gain of 200 (C pin1 to pin8 = 10uF).

     

    Out of curiousity, I tried simulating the input network (from jack socket to pin3 of the IC) and here's the response with the pot set to 100% and the input resistance of the amplifier as 50k (the typical value from the datasheet).

     

     

    image

     

    Even if the amplifier gain was less than 200 and the bandwidth of the amplifier was therefore higher, the high end -3dB point for the whole circuit would still be around 30kHz because of the action of C6 at the input. I don't know why C6 is there - possibly it is intended to filter out rf from medium wave broadcasts that might be picked up on the input leads and then get rectified by the semiconductors in the IC. Alternatively, it might be intended to reduce the possibility of oscillation at higher frequencies (even with the natural roll-off of the amplifier, the IC still has some gain at 1MHz where the possibility of capacitive coupling from the output to the input increases).

     

    For the output network, I tried simulating with a 8ohm resistor for the loudspeaker, but you should be a bit (very?) skeptical because I've just assumed the IC output is a perfect voltage source which it obviously isn't and an 8R resistor isn't a very good model for a loudspeaker. It does, however, give some idea as to what is going on and how it's going to behave.

     

     

    image

     

    Not surprisingly, the low end is dominated by the output capacitor and looks like it might be around 100Hz.

     

    So, overall we could say something like 100Hz-30kHz. That's fine for a small speaker and the kind of applications where you'd use the circuit. [It's only a simple amplifier and the distortion is more than 1% at higher frequencies, so we're not really in the realms of hi-fi here.]

Comment
  • in reply to DAB

    Page 4 of the datasheet has a graph of Voltage Gain vs Frequency. That shows about 40kHz for the IC itself with a gain of 200 (C pin1 to pin8 = 10uF).

     

    Out of curiousity, I tried simulating the input network (from jack socket to pin3 of the IC) and here's the response with the pot set to 100% and the input resistance of the amplifier as 50k (the typical value from the datasheet).

     

     

    image

     

    Even if the amplifier gain was less than 200 and the bandwidth of the amplifier was therefore higher, the high end -3dB point for the whole circuit would still be around 30kHz because of the action of C6 at the input. I don't know why C6 is there - possibly it is intended to filter out rf from medium wave broadcasts that might be picked up on the input leads and then get rectified by the semiconductors in the IC. Alternatively, it might be intended to reduce the possibility of oscillation at higher frequencies (even with the natural roll-off of the amplifier, the IC still has some gain at 1MHz where the possibility of capacitive coupling from the output to the input increases).

     

    For the output network, I tried simulating with a 8ohm resistor for the loudspeaker, but you should be a bit (very?) skeptical because I've just assumed the IC output is a perfect voltage source which it obviously isn't and an 8R resistor isn't a very good model for a loudspeaker. It does, however, give some idea as to what is going on and how it's going to behave.

     

     

    image

     

    Not surprisingly, the low end is dominated by the output capacitor and looks like it might be around 100Hz.

     

    So, overall we could say something like 100Hz-30kHz. That's fine for a small speaker and the kind of applications where you'd use the circuit. [It's only a simple amplifier and the distortion is more than 1% at higher frequencies, so we're not really in the realms of hi-fi here.]

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