Scrounged together an amplified speaker...

starhawk

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...for soldering practice and for fun (I'm weird). It works OK. It's loud and it's a little buzzy (boo) but it does make noise so I did *something* right :p

Based on an insanely simple LM386-and-a-single-big-cap circuit I found on Google somewhere. Only real mod I made was to add a 100nF (MLCC "104") cap at the power input.

Here's where the parts came from...

Speaker was from an old PC. IIRC it was an IBM NetVista. (Nobody cares.)
Big cap came out of the remains of the printer that put my mother through lawschool. (That Canon BJ100 was an awesome little printer.)
The LM386 power amp chip was left over from another project. (Specifically, it is an LM386N-1; not sure of the manufacturer -- logo is two horizontal lightning bolts.)
Power jack came out of a cheapass battery fan from Wal*Mart.
Vol control (with built-in switch) came from some stuff a friend (not local, but not on [H]) sent me. 10kOhm, audio taper.
Had the DIP socket, tiny cap, and headphone jack from various other past stuff.
Perfboard was purchased from Radio Shack a while back. The other half I have a project for as well -- but that one won't happen for a while yet...
Wires came out of a Sanyo Betamax player (or, rather, the remnants thereof) that was The Official Betamax Player Of The 1984 Olympics. LOL.

I'm using it with a deplorably random 9v 1a wall wart that is almost certainly unregulated.

Links to larger images...
http://i.imgur.com/t3ffLOw.jpg
http://i.imgur.com/xNBCFuu.jpg
http://i.imgur.com/mgE5m08.jpg

Here's pics...

Completed circuit, after soldering...


Added tape for wire-strain relief...


...and here's the plans I had drawn up last night on how I wanted to do it. (Protip: turn your head to the left -- I did not rotate this one and I should have.)
 

starhawk

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Slight correction -- the speaker is only buzzy when I'm holding the potentiometer body, and only then at lower volumes. I think it's me, not the circuit :p

Also, this thing vibrates my desk a little when it's playing America's A Horse With No Name -- dunno about anyone else, but my copy is a quiet one -- meaning, holy shit this thing is good :D
 

Mohonri

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Dunno how I missed this. Neat little project, and a good starter for someone just getting into electronics.
 

Arcygenical

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Get a better power supply. Like, really. ;)
Grab a LM386N-4 from ebay, and run the circuit @ 12v instead.

Will give you approximately 1w of output power.
 

starhawk

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According to the datasheet I *could* run this off of a regulated 12v supply. (Absolute dead maximum is 15v for that chip.) However, my two 12v wall warts are unregulated and are 15.5v no-load.

The DVE DV-91A wall wart (from places unknown) I'm using now makes plenty of racket with this circuit, I assure you.

That said, I am tempted to pick this up --> http://www.ebay.com/itm/371004745473
Will I have to alter any other part of the circuit? The big cap is rated 1000uF 35v (it's what I had). The small cap is an MLCC 104, but I don't know its voltage rating. It's tiny and yellow if that's any help.

BTW -- what manufacturer made the chip in that eBay link? The current IC is from the same manufacturer.
 

starhawk

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Outstanding questions...

That said, I am tempted to pick this up --> http://www.ebay.com/itm/371004745473
Will I have to alter any other part of the circuit? The big cap is rated 1000uF 35v (it's what I had). The small cap is an MLCC 104, but I don't know its voltage rating. It's tiny and yellow if that's any help.

BTW -- what manufacturer made the chip in that eBay link? The current IC is from the same manufacturer.
 

starhawk

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Whether or not it's a drop-in replacement was my most important question. I suspect that it is, but I wanted to be sure.

I *am* still a n00b with this stuff...
 

starhawk

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Whether or not it's a drop-in replacement was my most important question. I suspect that it is, but I wanted to be sure.

Oh duh... same pinout. So it's a drop-in for sure.

Hope the caps can take it :D

EDIT: purchased that chip from eBay...
 

starhawk

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I got the new chip this morning, and I'm about to put it in... this should be interesting :D
 

starhawk

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Put the chip in... with the old adapter, it pops when it hits a loud note, now. The higher the volume, the more it hisses and pops.

With the new adapter (DVE DV-1280-3M for 3Com) it buzzes extremely loudly upon powering on. I didn't bother putting music through it with that adapter.
 

starhawk

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Put the chip in... with the old adapter, it pops when it hits a loud note, now. The higher the volume, the more it hisses and pops.

With the new adapter (DVE DV-1280-3M for 3Com) it buzzes extremely loudly upon powering on. I didn't bother putting music through it with that adapter.

I'd like to know why it does this.
 

starhawk

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Put the chip in... with the old adapter, it pops when it hits a loud note, now. The higher the volume, the more it hisses and pops.

With the new adapter (DVE DV-1280-3M for 3Com) it buzzes extremely loudly upon powering on. I didn't bother putting music through it with that adapter.

...still wondering why this happens :(
 

Mohonri

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Pop on loud noise means that your amplifier is clipping--the output voltage is getting close to the power supply voltage. Give it more voltage or drop the volume.

Loud buzzing likely means your power supply isn't getting filtered out. Put a bigger capacitor on the input power supply lines. Or, better, put a properly-sized inductor in series with the power, before it gets to the cap.

It also appears that you have your signal and GND contacts switched on your audio jack. Tip is Left channel, Ring (which you don't have in this case) is right channel, Sleeve is ground. That shouldn't actually make a difference in this case, but keep it in mind in the future.
 

starhawk

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*sigh* I really don't want to rework the board for the one chip. I can fix the signal/ground bit on the jack, that's easy -- but adding another cap on the input is not trivial for the way that board is laid out. Not to mention I don't know what cap to put in -- I *do* know that I probably don't have it... (FWIW I'm thinking 10uF 35v across the 104 MLCC)
 

Mohonri

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You've got plenty of space to add capacitors and inductors to your perfboard. Sure, you'll have to rearrange a couple things, but IMO it *is* pretty trivial.

As for cap size, the bigger the better. Without seeing a waveform on an oscilloscope, I can't say exactly how much, but I'd start with a minimum of 100uF and preferably a 1000uF.
 

starhawk

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By "laid out" I meant the way it was wired up. Point-to-point, with some wires being implemented as solder-blob 'traces' (don't remember the proper term for that). To add a cap, I'd have to move four wires and redo some of the blobs. My soldering skills are not wonderful to say the least -- I had a lot of trouble getting that board to where it is now.

I know I don't have another 1000uF 35v cap for sure.

At this point I'm considering putting the old chip back in (it worked quite fine for me) and sending this new one back. I can think of several things I'd like to do with that ~$4 anyways.

EDIT: ~$5, not ~$4. Whatever.

EDIT2: old chip is back in. Sounds great! (It's a little scratchy but at this point I don't really care. If I ever do... I'll change the speaker.) New chip is going back to eBay. Not worth the trouble of futzing with IMO, I'd have to redo half the perf. No thanks.
 
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westrock2000

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Popping can also indicate that DC (0 Hz) is getting to the output and going to the speaker. You can use a capacitor inline with the speaker to try. This is how tweeters are cheaply protected because tweeters do not have the excursion (Xmax) that a DC signal tries to do. The downside is that in order to pass midrange frequencies you need a decent size capacitor. Though a bipolar capacitor of that size would probably only be a couple dollars.

And depending on your knowledge level: Internally a capacitor is not connected on each side. The layers of material are only very close to each other. Thus it requires frequency in order to jump between the layers. That is why a capacitor cannot pass DC.

Now here's a super secret that you should not tell anyone. If you go to a major semiconductor companies website (like Texas Instruments) you can almost always request free samples of standard catalogue parts. I recently ordered 5 each of LM7805 and LM7812 from TI for a project I am looking at and I had them within 2 days. You can get all kinds of basic chips from these companies for free. I even got a sampler of PIC's from Microchip about 10 years ago. I never ended up using them, but it's nice to have.

I even got lucky enough about 10 years ago to get 4x Apex PA45 Op Amps for free. I will probably never use them, but those are like $70-80 a pop. They are even the dangerous ones that have Beryllium Oxide (BeO) in them.
 

westrock2000

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Hey OP, even though your project is a little "rough" to say the least. I completely understand the sense of accomplishment that stuff like this brings. It can be very self gratifying. You just have to be careful, because it can become an expensive hobby VERY quickly if you get sucked in to much.

You might check out diyaudio.com forums. Active community over there, though some are a little on the high horse after all these years.
 

starhawk

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Not really interested in diyaudio.com, TBH, as I'm not an audiophile and I don't have the money to be one. The idea of paying more than $20 for headphones seems a bit silly to me -- and even $20 is a stretch. I have what I consider a nice pair, had from Wal*Mart in the clearance aisle for $13. They're the Philips ones that are just two fabric blobs connected by a thin wire 'headband' -- very simple. Mine are grey and are about on par with a good set of 2.0ch PC speakers.

I just like to play with electronics, and the amplified speaker happened to be something I could throw together with crap I had at the time -- which is why I did it. It was a fun doohickey to put together, that's all.

I'll probably upgrade the speaker -- this one's buzzy now -- and if I can find a pretty little box to put it in, it'll get an enclosure.
 
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