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LM386 Amplifier Module help

Discussion in 'General Electronics Discussion' started by Tombones, Dec 4, 2014.

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  1. Tombones

    Tombones

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    Dec 4, 2014
    Hello. So I joined this forum after several days of looking for answers without success. I'm not a regular user of forums which is why I didn't want to join, however, this is what they are for, yes?
    Hopefully someone here can help me get a grip on my project.

    I'm building some Monoboxes, but I'm not really savvy in the circuitry arena. I have looked at many of the vids and tuts on using the LM386 module and decided that it makes more sense just buy them already built. Which I have done. Most of the wiring, I believe, I have set (see image) but I have some remaining issues.

    Can I power the module via AC? Actually, can I use an old cell phone adapter for this task?
    If so, how would I wire such a setup?

    Will this module drive a 4" woofer and a 2" tweeter in mono or should I just use a full range driver?
    If I can run both, how would that be wired?

    I'm posting an image of the exact module I have with my notes. Hopefully it's helps.

    I'm hoping I'll get some helpful info. as I really do want to try this project. I'm a hands-on learner and once I do it, I got it.

    Sorry this is so long for a first post.

    Tom
     

    Attached Files:

  2. davenn

    davenn Moderator

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    Hi tombones
    welcome to the forums :)

    no AC power doesn't go anywhere near the board
    you have already shown your +5V connection to the board to operate it
    get you 5V from a plugpack power supply :)

    not likely, the amplifier is designed a run a small around 1W 8 Ohm speaker maximum

    also you have shown your input connection from the mono plug to the board reversed
    ---- swap the green and black wires


    cheers
    Dave
     
    Last edited: Dec 5, 2014
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Hi Tom and welcome to Electronics Point :)

    The LM386 is a very old design and there are much better options available. More modern devices can deliver much more power for a given supply voltage because they have a wider output voltage swing and use a trick called BTL (bridge-tied load), and they also have lower distortion.

    There are many preassembled modules available on eBay with a range of output power specifications. If you want something small, in the range of a few watts, search for PAM8403, IS31AP4991, NCS2211, TDA7052, TDA2822/D2822, TEA2025, LM4990, or TPA6211. These are all small BTL audio amplifier ICs that are used in these modules.

    You can drive two speakers from a single amplifier using a circuit called a crossover, which splits the frequency range into low and high bands. Proper crossovers have several inductors and capacitors, but you can get a similar effect by connecting the main driver directly to the amplifier and connecting the tweeter with a capacitor in series. This capacitor attenuates the low frequencies at the tweeter so it doesn't get damaged trying to reproduce the large low-frequency movement. If your tweeter is a capacitive type, you can omit the capacitor and connect both drivers straight to the amplifier.

    Finally to answer your original question... These boards all operate from a DC supply and may be damaged by AC. Most wall adapters produce a DC output, but some produce AC. These are generally the older, heavier ones. The label should say whether the output is AC or DC.

    I'm not sure what your application is, but if you're talking about 4" drivers, I think you may need more than a few watts to get decent sound with reasonable bass and low distortion. In that case I would go for a more powerful amplifier, and these require a higher supply voltage - often 12V or more. You can buy wall adapters with 12V and higher output voltages, and I recommend that you do. You need to consider their current ratings as well; a 12V 1A supply can provide 12 watts (power = voltage × current) which translates to around 5~9W at the speaker, depending on amplifier efficiency.

    Finally, modern wall adapters are the switching type - they operate internally at a high frequency, so they can be more compact and much lighter than the older type - and this high frequency can appear at the output and cause noises in sensitive audio circuitry. This is more common with cheap adapters where the manufacturers save a few cents by omitting components that filter the output to remove this noise. If you have problems with this, you have the option of adding some filtering components yourself.
     
    (*steve*) and Bluejets like this.
  4. davenn

    davenn Moderator

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    thanks Dave :)
     
  5. Tombones

    Tombones

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    Dec 4, 2014
    Thanks for the welcome and the answers!

    Okay, so AC is off the table. I have 9V plug/caps that are prewired with a red and black. Looking at the diagram, Red goes to VCC and Black to GND (-ve)? Is that right?

    Otherwise, I'll reverse the wires on the jack and go with a small, full range speaker.

    KrisblueNZ, My application is small, portable speakers for MP3 players. I have five of the LM386 modules already to use first. Great suggestion on the others though. I'll be sure to look into those to build better/louder speakers.
     
  6. davenn

    davenn Moderator

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    Okay, so AC is off the table. I have 9V plug/caps that are prewired with a red and black. Looking at the diagram, Red goes to VCC and Black to GND (-ve)? Is that right?

    9VDC is OK for the LM386

    hope you are not disappointed ... the output will be quite low


    cheers
    Dave
     
  7. Tombones

    Tombones

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    Dec 4, 2014
    I understand 9V will work, I'm not sure I understand where the black and red wires from the 9V attach to the board. Actually, should I be using some other battery pack for better output?
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You may have misunderstood. As I read it, you have some AC adapters that probably produce DC outputs.

    As Dave has said, the AC doesn't go near the amplifier, but the plugpack (normally -- See Kris' post) contains the circuitry to change it to DC.

    If you are still unsure, post a photo of the information that is printed on the plugpack and we'll decode it for you and show you what you need to look for.

    And welcome to Electronics Point.
     
  9. Tombones

    Tombones

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    Dec 4, 2014
    Let me post the specs from the seller. Do these numbers change anything as far power supply goes?

    Features:
    1. Onboard LM386 Chip
    2. 200 multiplier benefits circuit design
    3. On-board speaker wiring block
    4. On-board 10K variable resistor, you can adjust the volume
    5. Onboard power indicator
    7. Operating voltage: 5 ~ 12V
    8. Board size 41 (mm) x13 (mm)

    If operating voltage is as stated, why can I not use a 5V or higher power adapter?
     
  10. Tombones

    Tombones

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    Dec 4, 2014
    Oh wait. I had to look up "Plugpack." Didn't realize what that was. I've been calling it an "adapter." My bad.

    So, Steve, I'd like to salvage a Plugpack from a cell phone. Can you clue me in as to what information I need to be looking for? Also, using a Plugpack will help with the output/sound, I assume.
     
  11. davenn

    davenn Moderator

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    That's OK ... just different terminology, depending on what country you are from
    plugpack is a little better as an "adaptor" could mean a dozen different things without context ;)

    all cellphone chargers are 5VDC and probably somewhere in the 500mA to 1A. That will be OK :)

    only in that with no power source you wouldn't have any sound out ;)

    Dave
     
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Yeah, "plugpack" is just another name. Often they are called "wall warts" because they sit against your wall and look like a big black wart.

    Whatever you call it, they take power from the AC line (which some of us call "mains"), either 115V AC or 230V AC, and they convert it to a lower voltage. My info in post #3 refers only to the output of the wall wart, since the input is simply your AC line voltage.

    If your wall warts have a red wire and a black wire, they're probably DC. You can check this with a multimeter, and a multimeter is worth getting (see ).

    So the LM386 modules need 5~12V. That's DC. And a 1A current rating would be fine. So any wall wart that has a DC output voltage in that range, and is rated for at least 1A, will work.
     
  13. Tombones

    Tombones

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    Dec 4, 2014
    Ha! Wall wart I have heard before. I have a 12V wart that I'll use. No red and black wires, but I do have solid black and black with gray dashes.

    I don't want to fry these modules due to my ignorance, so can you offer help with wiring the wart? My module has four prongs. Two in the middle are for the source jack. Will I use the other two for power? If so, do I connect the wart directly to the module or get a female jack to plug the the wart in? Also, which wire goes to the +5V (VCC) prong and which wire to the GND prong?

    You guys have been a huge help. I'm getting much out of this. Thank you!
     
  14. davenn

    davenn Moderator

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    use your multimeter to confirm which is positive and which is negative
    also confirm that the voltage is 12V, before you connect it to the module


    that's what the markings on the module says

    strip a little of the plastic insulation off the ends of the wires from the plugpack. Identify which is positive and which is negative and connect them as per the markings on the module
    and as per the pic in your first post


    which do you think ? ;) see previous comment/your pic
     
  15. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    As Dave says, use a multimeter set to the DC volts range (20V DC if it's not an auto-ranging meter) to determine which wire from the wall wart is positive and which is negative. Try them either way round until the reading is positive (no "-" sign on the display). The wire that's connected to the red probe is positive and the other wire is GND.
     
  16. Tombones

    Tombones

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    Dec 4, 2014

    Right. I do have a meter. Guess I should spend some time getting more familiar with it.

    Thanks for all the help. If you don't hear from me again, it's because I blew myself up! :eek:
     
  17. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    LOL!
     
  18. Tombones

    Tombones

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    Dec 4, 2014
    Well, I didn't blow up. However, I can't get any sound out of the cursed thing. While I keep trying to get this to work, I seek opinions on better versions.
    What I want to do is build single, amplified, mono speakers for small spaces. I would like them to sound good enough to surprise people. Of course, I need to keep cost down. I'd like to use two drivers (mid-bass and tweeter?) and not just a full range speaker.
    Some amp modules have been suggested above, thank you, I just need to know which one is best suited for my potential application.

    Thanks guys.
     
  19. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I guess your choice of speakers and enclosure will be pretty important. Perhaps you could find a forum for discussion of acoustics, and describe your whole project in detail - don't force them to play guessing games with you, please - and see what they suggest. We can advise on the electronics side.

    The amplifiers I listed back in post #3 can deliver a few watts, maximum. If you need more than that, there's a range of single-chip amplifiers available with output powers up to 100W and even higher.

    Here's a Digi-Key part filter that should include all suitable devices that Digi-Key stock (and they have probably the widest range of any retailer). I've selected mono devices with output power between 1.5W and 50W (though I think 10W will be plenty), in through-hole and SMT packages but excluding no-lead and BGA packages (which are difficult to prototype with): http://www.digikey.com/product-sear...nSort=1000011&stock=1&quantity=1&pageSize=500
     
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