Cheapest Speaker Amp

Search on "Gain Clone".

Here is a good place to start:

http://diyaudioprojects.com/Chip/chip.htm

The cheapest speaker amp comes in a circa 1985 receiver from your local good-will store, or a garage sale. It will probably cost about $25.

As an added bonus it will often come with a decent radio-tuner and probably a phono stage to play your fuzzy warbles on too!

The $25 (local average price, probably not more where you live) that the local thrift-store asks for old receivers doesn't buy you the transformer for a 40W gainclone, never mind heat-sinks!

If you are looking for a fun project that represents a decent compromise of price and performance, the gain-clones can do quite well. The whole family is pretty well documented, and offers some interesting upgrade paths. 

If Goodwill turns out nothing, try craigslist ..dB

http://audiokarma.org/forums/showthread.php?t=126730

I got mine at RadioShack for the close out $15, someone has them on EBay for $30

but much better built, metal case used amps are available as mentioned above

try this

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=320603376236&fromMakeTrack=true&ssPageName=VIP:watchlink:top:en

Quote:

Originally Posted by Pingupenguins 

Very nice. I still don't understand how to do a power supply though. It asks for a AC dual 20-28V 200W I'm assuming I have to buy a donut looking thing and hook it up. Why do I buy donuts or power supplys in general? Also is that like a Gain clone?

That's essentially a gain clone. 

You want a 200VA donut looking thing with dual secondaries in the neighborhood of 20 to 28 volts. You can get a good deal on that sort of thing at antekinc.com. (Edit: almost all of their toroids have dual secondaries, fwiw)

Also, if you plan on driving 4ohm speakers with a chip amp, you need to aim lower rather than higher for the transformer voltage. 2x18v would be the lowest you would want to go, ideally not more than 25v for 4ohm speakers. 

But like others have said, a vintage amp from local goodwill or craigslist will cost less than the donut looking thing, if you don't need the rush of DIY. 

Why, one day this summer i was trawling yard sales for a hot plate to build a smoker with when i came across a stack of Onkyo stereo components from the late 90's. I was sizing them up and figuring i'd lowball the amplifier at $20 and offer $15 for the preamp when the owner sidled up and said he'd take $20 for the whole stack. 

I decided not to argue. He decided to make me take everything else that looked like a stereo component with it. 

In the end i brought home a 2x150w power amp, a preamp, a tuner, an eq, a prologic decoder with three more smaller amp channels in it, and dropped off a cable box, a couple VCRs, two cassette decks, and a videodisc player at the goodwill on the way home. 

I also have a 2x115w Kenwood power amp that i picked up for $10 at goodwill a couple years ago. Not super great sounding, but nothing that can't be fixed by putting a tube preamp in front of it. 

yeah, it's a gainclone amp with lm3886 ( pcb + parts + pcb for powersupply), But you need to buy donut thing +- 24volt + heatsink + chasing, i guess around total $100, otherwise just go to goodwill store or fleamarket (used n old amp, probably under $50) 

tube preamps often require the use of potentially much more dangerous/lethal donut looking or R-core things and i would never recommend such a thing as a first project before you even know what the donut looking things do and their place in the power supply

toroidal transformers

Quote:

Originally Posted by Pingupenguins 

Yeah i knew they are transformers. I'm used to the box transformers not a "Toroidal" transformer. I realize the transformer is copper wire wrapped around a iron core that causes electrons to move in the adjacent wire and the number of turns dictates the the voltage stepped down or up from stock 120v or 240v depending on what country you live in. I also know that the current is alternating. Blah blah. I took one year of HS physics and am in AP Physics this year. We never learned about toroidal transformers aka donuts. So I figured I'd call it a donut so people might get a chuckle, but I'm not a completely slow noob DIY. I ask before I build and I know how dangerous power supplies are, VERY lethal.

I have a quick question about power supplies, why do computer PSU's have fans? Is it to cool the coil or circuitry inside? What wattage PSU can I salvage from a old comp?

Computer psu's tend to be of a higher wattage, with more power rails than your typical amplifier, so more heat.  Also, the fan in a computer psu serves a second purpose of pulling air out of the top of a computer case.