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Old 22nd April 2010, 10:20 PM   #1
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Join Date: Apr 2010
Default How can I build the cheapest amp?

Hey, I am helping a friend build a talk box for his band and I thought I could build him an amplifier for cheaper than he could buy one from guitar center.
I was looking at all of the schematics and the largest cost seemed to come from the center tap transformers or smps systems.

I have lots of high wattage +12 power supplies, are there any schematics with that as the needed voltage?

I am looking to build something 100w rms.

It can sound like crap, it just needs to move air.
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Old 22nd April 2010, 10:57 PM   #2
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Location: Cacak, Serbia
You might try with IC TDA1562Q.
Laonicus Chalcondyles : “Tryballos = Serbos, autem gentem esse totius orbis antiquissimam et maximam, compertum habeo...”
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Old 22nd April 2010, 11:17 PM   #3
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Does this look like a good schematic?
Also, is it difficult to find that part since it is out of production?
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Old 22nd April 2010, 11:52 PM   #4
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Originally Posted by waerzxxx View Post
I have lots of high wattage +12 power supplies
You can use an old car stereo, many are 4*40W.

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Old 23rd April 2010, 12:56 AM   #5
godfrey is offline godfrey  South Africa
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What kind of amp do you want? - Guitar amp / home audio / PA / something else?

If you combine a few 12V supplies to get a higher voltage, it'll be a LOT easier to get high power. e.g. Use four to make a +-24V supply.

With that supply, you could use e.g. two LM3886 bridged to get about 100W into 8 ohms with good quality.

edit: The one you linked to will give about 30W into 8ohms, but probably not very good quality.

Last edited by godfrey; 23rd April 2010 at 01:00 AM.
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Old 23rd April 2010, 01:49 AM   #6
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Thanks so much for your rapid and knowledgeable help.

I just realized my power units have -12 and +12 so I can get it up to +-24 with only 2 units.

It is just meant as a pa amp that is going to a voice box. It can sound mediocre without really causing an issue.

Would something such as this
Click the image to open in full size.
or this
2 x 68W Watt LM3886 + NE5532 Audio Amplifier Board - eBay (item 230464954808 end time Apr-24-10 19:25:06 PDT) work well?
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Old 23rd April 2010, 05:15 AM   #7
godfrey is offline godfrey  South Africa
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Location: Cape Town
If those are computer power supplies, the -12V is probably useless. PC supplies are normally rated for high current at +12V and low current at -12V. e.g. I've got an Asus 450W supply that's rated at +12V: 29A, -12V: 0.5A

When daisy-chaining multiple supplies, you have to be careful about the earthing. You probably have to disconnect the mains earth from the individual supplies, and connect it instead to the final "0V" common point (and the amp's chassis). Each supply's chassis will probably have to be insulated from everything else too.
The ebay amp you linked to looks like a stereo amp. It will work with +-24V supplies, but only give about 30W. For full power, +-36V would be better.

I was thinking of a bridged amp (as shown on page 5 and 6 of this PDF), because it allows you to get more power with lower voltage supplies.

The ebay amp's a nice price though, and you could always hack it into a mono bridged amp. Or just DIY your own amp. Either way, you'll need a decent heatsink.

btw: What's a voice box? Is this what you're talking about?: Talk box - Wikipedia, the free encyclopedia
If so, it won't need very much power, will it?
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Old 23rd April 2010, 08:49 PM   #8
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Yes, I did mean talk box. My estimations for power needs might be too high, I was just looking at buying a 100watt Horn Loudspeaker at walmart and enclosing it with a tube to make the voicebox.

I think I will just find a smaller loudspeaker and build a different amp about 25watts or higher.

It is kinda disappointing when I looked at my PSU's -12 it only does .25 amps.
My reason for using the computer psu was because when I added up all the parts on dig-key I would spend far more on the Transformer and power supply than the audio amp.
If there is any lower power solution that you think would be a better cheap solution than using a TDA1562Q?
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