MP3 Player into LM386N-3 Amp

Discussion in 'General Electronics Chat' started by tracecom, Dec 3, 2011.

  1. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
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    I want to listen to my MP3 player (Sansa Clip +) in my truck (which has no auxiliary input to the radio) and I don't want to fool with an RF transmitter. It's against the law to wear headphones or earbuds, so I have breadboarded an amplifier using an LM386N-3. It's the Amplifier with Gain = 20 example on P. 5 of the attached datasheet. In addition to what's there, I have added a .1μF and a 10μF cap across the power leads of the amp, and I have a 10μF cap coupling the output from one side of the MP3 player directly into pin 3 of the LM386 (no 10K pot.) I plan to use the volume control on the MP3 player to control the sound level. I also don't have a .05μF cap to go on pin 5, so I am using a .1μF.

    It seems to be working, although I still have some noise issues, but I think they will work out when I shorten component leads and eliminate clip leads. I am planning to build this up on a piece of perfboard tomorrow, but are there changes I should make first?

    Secondly, I don't need stereo and would like to combine both outputs from the MP3 player and feed the combined output into the LM386. Would someone post a simple circuit for combining the outputs? Thanks.

    BTW, I am leaving the computer now (to go to a Christmas concert) so I won't be responding to posts until much later tonight.

    Thanks again.
     
  2. Audioguru

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    Dec 20, 2007
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    The LM386 amplifier is a little toy.

    With a 13.6V supply the LM386 will have an output of only 0.65W into 8 ohms at clipping (like a cheap clock radio) but it will heat with 1.1W which will overheat and destroy it.
    It is designed for a 9V maximum supply and its case is not designed to have a heatsink like a real power amplifier IC.
    You should reduce the supply to 9V with a 9V voltage regulator IC plus two capacitors. Then the output will be only 0.56W into 8 ohms at clipping and the max heating will be 0.6W.
     
  3. thatoneguy

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    A good FM transmitter output with your factory stereo will sound far better than anything you'll build with a LM386. If you get a higher quality FM transmitter, it will sound perfect.

    Don't skimp on the FM Adapter, some don't transmit in stereo, even though they are labeled "stereo", they are just adding L+R so both stereo channels are transmitted, but not separated.
     
  4. tracecom

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    Here is a photo and a schematic of the finished prototype.

    [​IMG]

    [​IMG]

    It works reasonably well, although as predicted, there is some distortion at high volume. I think it will serve my intended purpose.

    ETA: I added R4 in order to reduce the gain from a maximum of 200 to a maximum of 50. It seems that this change reduced the amount of distortion at medium and high gain, although now the MP3 player volume must be increased to produce the same perceived volume from the speaker.
     
    Last edited: Dec 5, 2011
  5. Audioguru

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    Actually, the distortion is fairly low at about 0.3% up until clipping.
    It doesn't have high volume because if the battery is brand new and is still 9.0V, the output power into 4 ohms at clipping is only 0.32W which is less than a cheap clock radio.

    Two simple things will make it sound much better:
    1) Increase the value of C5 (now only 0.1uF) to 1000uF because the battery has an internal resistance and its voltage fluctuates with low frequencies.
    2) Increase the value of C2 (now only 220uF)to 1500uF because it cuts bass frequencies below 182Hz.
     
  6. T.Jackson

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    Nov 22, 2011
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    That's a very neat looking proto that you have there.

    Try having a go with the LM1875, or the LM3886. There isn't much more involved with them really, and their performance is comparable to a class AB BJT-based amp. Particularly the LM3886.
     
  7. T.Jackson

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    Nov 22, 2011
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    @Audioguru,

    The LM380 is better for only 2 more cents yeah?
     
  8. tracecom

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    Thanks for your input; I tried both suggestions.

    1) This made no difference that I could notice. Perhaps this is because of my poor hearing (due to too many years of too much rocking and too much shooting) or maybe it's the crummy speaker.

    2) I could detect a small increase in bass, however what I neglected to state in my first post is that I listen to very little music on the MP3 player; I mostly listen to talk podcasts, so the added lower frequencies don't help.
     
  9. tracecom

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    Thanks.

    I might do that; I enjoy experimenting.
     
  10. T.Jackson

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    Nov 22, 2011
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    Try the LM380. It's about the same price and offers better performance. It is loud enough at 2WRMS for a lot of people. I did build an amp for a Tafe college project many years back, and when I brought it into class to show it off (playing some loud music) -- the storeman next door to the class was furious.

    A few of the LM3886 ICs out of phase might get your neighbour down the street into a state where they want to throw a chair through your window, which was the case for me.
     
  11. Audioguru

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  12. T.Jackson

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    Nov 22, 2011
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    Use two batteries in series then.

    With reasonable sound quality it is ok for 1WRMS ?
     
  13. Audioguru

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    Sure, simply double the battery voltage and use an LM380 amplifier IC. But then the output current is also doubled and the small lightweight 9V batteries will die in a few minutes. The LM380 amplifier IC might also die of overheating.

    The LM380 is designed to drive an 8 ohm speaker but it can drive a 4 ohm speaker if its supply voltage is low (then the output current is low enough).

    1W RMS into 4 ohms is 5.6V peak-to-peak. A little amplifier will probably have a 5V voltage loss so the supply must be at least 10.6V.
     
  14. tracecom

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    @Audioguru,

    Do you have a circuit you would recommend for my purposes: take the output from the headphone jack of a Sansa Clip +, combine stereo to mono, into an amp, and thence into a 4 ohm speaker, with sufficient volume to be heard in a moving vehicle, and with the output centered on voice frequencies (30 to 3000 Hz)?
     
  15. Audioguru

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    There are about 120 car radio ICs available. Most have an output of 14W into 4 ohms when powered from a charged car battery.

    But most electronics parts distributors do not stock them because nobody buys them anymore.

    Digikey has many TDA2003 ICs in stock. Its output is about 3.8W into 4 ohms.
    They also have many TDA2005 ICs. The output is about 14W into 4 ohms.
    The datasheets have schematics and recommended pcb designs.

    Speech has vowels from about 80Hz to about 3kHz. But important consonants (s, c, t, sh, ch, th and many more) extend to 14khz. Many deaf people hear only vowels (grunts and groans).
    What did you say??
     
  16. T.Jackson

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    Nov 22, 2011
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    Keep going. You'll drive the price of them down, then we can buy!
     
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