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Thread: electronics folks please help

  1. #1
    PSB Statesman Dubs's Avatar
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    electronics folks please help

    I am not very electronic minded but I am learning.
    I bought a few of these to make a couple of battery powered portable guitar practice amps. Amazing sound is not the goal but portability and a raw sound would be perfect

    https://www.ebay.com.au/itm/LM386-Mi...53.m2749.l2649

    I plan on running them on a 9v battery and want to know if the size of the speaker will matter in battery draw? Or even if I'm dreamin on trying to get this to work.

    I have done some work on the boards this weekend extending the on board parts to mount externally in a small case



    Extending the volume, and adding in a guitar jack, on off switch and extending the LED to mount in a small box - all now soldered onto the board.

    I also have a couple of these coming just as an alternative

    https://www.ebay.com.au/itm/Mini-LM3...53.m2749.l2649

    Any help or guidance appreciated, happy to look at other options or alternatives

    Dubs

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    Member Crobbo's Avatar
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    Get the LM386 datasheet.

    It will outline the ideal conditions for operation.

    Sorry can't link it from my phone.
    In sterquiliniis invenitur.

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    Member Halo_2's Avatar
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    You only get 100 - 1200 mAh from a 9v battery, wire two in parallel voltage stays the same but your amperage doubles.

    Size of speaker will matter on the run time aH (everything is relative to each other ohms law)
    "Some people are like clouds. When they disappear it's a beautiful day"

  4. #4
    llbuono
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    I am not an electrician like halo but i have seen an idea in the early 70's by my grandfather and english radio amateur he wired twenty four c cells in parallel to give him six volts and a longer battery life for his portable transister radio before those power packs were thought of.

    Another idea is a model boat sealed lead gel battery they come in six and twelve volts exactly you could wire two six volts in series to give twelve volts or just use one large capacity twelve volt one.

    This is what the busker's in the city use i believe you may however have to add a resistor or a variable potentiometer, you can find circuit diagrams on google or just go to jaycar, altronics or even most rc hobby shops so you can reduce the voltage to nine volts.
    I hope this is of some assistance to you dubbs

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    Member BusaSteve's Avatar
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    I think an important question needing an answer would be where you propose to practice...so we can avoid going there...
    Smoke me a kipper...I'll be home in time for breakfast
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    Member Water pig's Avatar
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    Why not use a battery out of a cordless tool? Very light / portable / powerful enough to run a decent speaker and fully rechargeable

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    Member GsxInShed's Avatar
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    Quote Originally Posted by Water pig View Post
    Why not use a battery out of a cordless tool? Very light / portable / powerful enough to run a decent speaker and fully rechargeable
    Make the amp look cool use the drill/charger adapter to mount the battery then you can swap batteries in an instant..
    " Imagination is the seed of life..."
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    PSB Statesman Dubs's Avatar
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    so the single 9v battery wont cut it, the speaker i tried was these 2 and the power sapped uber quick
    https://www.jaycar.com.au/shielded-1...eaker/p/AS3030
    https://www.jaycar.com.au/40mm-all-p...eaker/p/AS3004

    I then plugged it into the wall using a 12v dc plug and it worked a treat

    It cant be all that difficult to get it to run off a battery when i read these
    http://www.instructables.com/id/The-...r-Guitar-Amp-/
    http://www.runoffgroove.com/ruby.html


    Dubs

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    Member Halo_2's Avatar
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    I would only use one 40mm speaker, water pig does have a good idea you could run inside a ryobi little bluetooth stereo.
    "Some people are like clouds. When they disappear it's a beautiful day"

  10. #10
    llbuono
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    Quote Originally Posted by Dubs View Post
    so the single 9v battery wont cut it, the speaker i tried was these 2 and the power sapped uber quick
    https://www.jaycar.com.au/shielded-1...eaker/p/AS3030
    https://www.jaycar.com.au/40mm-all-p...eaker/p/AS3004

    I then plugged it into the wall using a 12v dc plug and it worked a treat

    It cant be all that difficult to get it to run off a battery when i read these
    http://www.instructables.com/id/The-...r-Guitar-Amp-/
    http://www.runoffgroove.com/ruby.html


    Dubs
    The short battery duration is due to the high current drawn from the amplifier, have a read of my earlier post some radio controlled models especially the bigger model ships have a high current draw even with geared electric motors, since weight is not a problem they use very large lead sealed batteries with high amp hour ratings this is the type you will need.

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    Member MikeL's Avatar
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    Here's a copy of the data sheet for the LM386
    http://www.ti.com/lit/ds/symlink/lm386.pdf
    If you don't know much about electronics, it probably won't be all that useful for you.
    A small amp chip like the LM386 has a limited power output, mostly due to the limitations of internal power dissipation.
    From the datasheet, you can get about 0.5w straight out of the amp.
    Either of the speakers you linked to will work, they both have the same impedance of 8ohms.
    I wouldn't bother trying to work out how long a given battery will last, you are unlikely to get anything but a rough answer anyway, and in the end you just want the biggest battery (in Ah) that you can afford/fit in the box.
    Quote Originally Posted by mekon
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    Member Bill-2014's Avatar
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    Quote Originally Posted by llbuono View Post
    The short battery duration is due to the high current drawn from the amplifier, have a read of my earlier post some radio controlled models especially the bigger model ships have a high current draw even with geared electric motors, since weight is not a problem they use very large lead sealed batteries with high amp hour ratings this is the type you will need.
    A lot of the model aircraft now have motors powered by lithium polymer batteries
    3cell will give you 11.2v and you can get all different mah ratings



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    Member TurboR1's Avatar
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    Never mock the mighty 9V

    Trying to think of a wise and sincere signature quote, but the only words that leap to mind are, "TITTY SPRINKLES"

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    Member Frogger's Avatar
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    Dubs , have you looked into a VOX unit ? i got the vox headphone bass amp and its awesome and was only like $50. u can even get a small battery speaker that it hooks upto to give u a cabinet style setup with quite alot of controls.

    i personally use my gaming headphones but worth a look.

    https://www.youtube.com/watch?v=8hsK03wvbXg
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    New Member Nero Diablo's Avatar
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    You will probably be better off with something like a 12 volt security battery. Battery life will be directly associated with Watts out which is all dependant on the gain of the amp etc. However an A class amp is typically only about 30-40% efficient. B class push pull is around 50 and C which is never used for Audio (it leave a big chunk of the signal out in the the middle) about 70% so you can get a rough calculation off that.

    The more obvious solution set your multimeter up for current measurement put it in series of a power supply and measure the current, while running a signal through it. This will tell you current draw work out how much run time you'd like, it will be voltage dependant and some batteries will handle been totally discharged a lot better than others so you'll need to read up on the spec sheet of the battery you intend to use.
    Harvey community radio has a motorcycling show listen over the web here www.harveycommunityradio.com.au ,Facebook here http://www.facebook.com/pages/The-Mo...34691323302991 yes I am the goose that hosts it.

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