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Thread: cheap kit Audio amp question

  1. #1
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    cheap kit Audio amp question

    Hi All,
    I have a couple of sets of speakers for my computer. One is powered but the amp board got ruined over the years. The volume control with on off switch loosened up from the board, a bunch of traces peeled off, etc. I had gone in and fixed it (sort of), but its basically ruined.
    Started looking around for cheap audio amp kits, on a small board. Can anyone tell me how bad these are:

    https://www.ebay.com/itm/LM1876TF-30....c100010.m2109

    No heat sinks, so that's sort of a red flag. The layout of electrolytics looks sketchy (why use so many and not fewer higher value? )

    Anyway, curious if anyone has an opinion if this 14.00 thing would blow up in two days, or maybe OK.

    Its only going to be powering one or two small sets of speakers, for computer audio.

    Thanks.

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    Don't forget the joker g1's Avatar
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    You are supposed to mount on a heatsink. That's not uncommon for these kind of kits at that price.
    My worry would be whether the power chip is authentic. Even so, I'm sure they work, and your application is not too demanding as far as needing full power capability of the chip.

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    Quote Originally Posted by g1 View Post
    You are supposed to mount on a heatsink. That's not uncommon for these kind of kits at that price.
    My worry would be whether the power chip is authentic. Even so, I'm sure they work, and your application is not too demanding as far as needing full power capability of the chip.
    Cool, thanks. Sent the seller a q if they sell the heat sink. Found a few other kits, similar price, also no heat sink. I did search the web for "heat sink for LM 1876, but no hits.

    Yeah, I don't think this is a demanding app, just mostly low sound levels for my PC speakers.

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    Don't forget the joker g1's Avatar
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    Search for heatsink for output IC rather than specifically the LM1876.

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    Supporting Member TomCarlos's Avatar
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    Mike ....

    Take a look at this - https://pic-microcontroller.com/diy-...wer-amplifier/

    If you are pushing this chip, it gets HOT!! So you need a BIG heat sink!!

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    Supporting Member Jazz P Bass's Avatar
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    Why mess around with Class AB?

    I would go with a Class D stereo amp board with a volume control.
    https://www.ebay.com/itm/12V-24V-Blu....c100005.m1851

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    Lifetime Member Enzo's Avatar
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    Or buy a cheap working stereo receiver at a yard sale and connect the computer to that.

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    Thanks everyone. Reading and googling ...

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    Old Timer olddawg's Avatar
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    Go to a Goodwill Store or similar Thrift shop operation. They literally have piles of this stuff.

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    Quote Originally Posted by olddawg View Post
    Go to a Goodwill Store or similar Thrift shop operation. They literally have piles of this stuff.
    Sometimes pretty good stuff too.

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    DON'T FEED THE TROLLS!

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    Thanks everyone, read a bunch. Well, re class D: just didn't know what's good and what's not. I found a few other LM187X, a few 1875's, few come with heat sinks. The ones that don't, I emailed the seller and they have no idea. I think there must be 20 sellers that bought a big pile of the same unit from some wholesaler, or someone who went bust. They don't know what they're selling and don't know where to find parts like heat sinks.

    Thanks for the link to the project page. on the PIC site. The links there are dead but someone does have another site with the PCB files. I love to tinker, so might try that if I can still get boards made.

    Re buying cheap used, arrghh, this part of Eastern MA seem s like a dead zone for lots of used stuff for some reason. Our local craigstlist is chock full of 20.00 items selling for 150.00. <big frown> As an aside, looked forEVER for an old beat up 'scope, finally a friend gave me one that he had in his closet for 25 years that his wife sai "get rid of this or GO". All the throwaway junk is going for 100 and up. Most I wouldn't even take as a throwaway!!!

    Another reason for going board level, is I like to solder and tinker with stuff, but akk if I could get a cheap throw away receiver, or like 20 or 25 bucks, any model Id take it.

    Thanks for the tip on Goodwill. There's one not far from Nashua, a bit north of where I live.

    Geez all those years I lived on Long Island going to school, they had some absolutely fantastic yard sales. I had bought a really high end granite base turn table, with a high end cartridge for like 15 bucks back in the day. I see yard sales around where I live in Eastern MA, but dang its like a big pile of chipped dishes and some old clothes. No idea what these people do with their old Moog synthesizers, Fender and Gibson guitars and old stereo equipment!

    I think I should move!

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    Found a few heat sinks for the audio thing, if it came to that. Pricey!! Eek. They sell by the foot and its like 100 bucks. I don't need a foot, but even half that, would still be several times the cost of the whole kit. I can't convince myself that a piece of aluminum with little fins is worth fifty bucks. Longing for the old days of piles of old stereo equipment sitting on the side of the road.


    Forty bucks?

    https://www.mouser.com/ProductDetail...vvfWj95niGs%3D

    Its a piece of aluminum, not a new mercedes!

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  13. #13
    Lifetime Member Enzo's Avatar
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    Ever see a stereo in a dumpster? A dead one still has good heat sinks in it.

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    Old Timer olddawg's Avatar
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    Seriously... practically everyone that bought a a computer in the last 20 years got an amp and speakers with it... then chucked them when they upgraded or moved. I gave 6 of them to the Goodwill Drop Off when I moved last January. They all have a corner with the stuff stacked to the ceiling. Also good for power supplies, wall worts, etc. A lot of times the speakers and the amps get separated too and you get them for $1 or $2.

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    Quote Originally Posted by Enzo View Post
    Ever see a stereo in a dumpster? A dead one still has good heat sinks in it.
    Been quite a while. Used to, all the time. Have to keep looking

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    Quote Originally Posted by olddawg View Post
    Seriously... practically everyone that bought a a computer in the last 20 years got an amp and speakers with it... then chucked them when they upgraded or moved. I gave 6 of them to the Goodwill Drop Off when I moved last January. They all have a corner with the stuff stacked to the ceiling. Also good for power supplies, wall worts, etc. A lot of times the speakers and the amps get separated too and you get them for $1 or $2.
    Thanks O.D. yea there are two near me, will try this weekend.

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    Supporting Member eschertron's Avatar
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    I can pull dead computer power supplies out of the recycling bin at work pretty much any week of the year. I've got a small pile of heat sinks from those stockpiled.

    Also a nice chrome-plated PSU box (why would anyone ever need that in chrome?) to turn into a little bookshelf guitar amp, but that's another thread.

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    Quote Originally Posted by eschertron View Post
    I can pull dead computer power supplies out of the recycling bin at work pretty much any week of the year. I've got a small pile of heat sinks from those stockpiled.

    Also a nice chrome-plated PSU box (why would anyone ever need that in chrome?) to turn into a little bookshelf guitar amp, but that's another thread.
    Ooh, now that you mention it, there's an electronics/computer repair shop in the next town over. Its been ages since I drove past there, but they always had aHUGE pile of dead electronics on/around the garbage can out back. It took huge effort not to pull over and take a look. I'll swing by on the way home tomorrow. Its out of the way, but .... who knows maybe some good stuff in there!

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    Haven't found anything in the roadside, but did find one or two with heat sinks. FUnny, they are not much different in price.

    https://www.ebay.com/itm/TDA7377-DC1...aa7c%7Ciid%3A1

    The really funny thing, to me anyway (untrained eye), is that the heat sink appears to be mounted just wrong. The hottest part of the transistor is mounted on the thin part of a fin, and not on the solid part of the back of the sink. I don't believe their ME was tops in his/her class.

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    It looks like you could cut most of those fins off, and still have the same cooling.

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    Quote Originally Posted by dmartn149 View Post
    It looks like you could cut most of those fins off, and still have the same cooling.
    Heh, yeah, the A team didn't design that one.

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    Interesting. Looks like the exact same board. Fewer filter caps. But the heat sink is mounted correctly (or better anyway) on this one:

    https://www.ebay.com/itm/DC-12V-TDA7...aa7c%7Ciid%3A1

    And its a little over two bucks cheaper.

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    I was just about to write a "sadly, the old electronics repair shop is no longer" message, but I found the shop is still there, after 20+ years, just a few doors down. Hopefully, they leave a heaping pile of nice non recyclable electronics to throw out. With heat sinks!

    The development where my employer is located, used to have a self serve electronics waste drop off once a year. It was cool since that evening, I could 'browse' the junk. They had a big section in one of the garages. They stopped that and instead, a truck arrives between certain hours and you had stuff right to the guy who puts it in the truck, so no junk shopping for a long time. And our company used to TOSS really good, say 4-5 year old computers, now they have a recycler come and they record the serial numbers.

    Getting harder to get electronics junk anymore.

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