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Old 8th November 2007, 02:29 AM   #1
seth556 is offline seth556  United States
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Default How hard can it be?

Hi all,

I'm pretty much a noob when it comes to audio but I'm learning. I'm looking at building an amp that I can use to crank out the music from my computer, nothing crazy powerful but I still like it to get loud at times. And I'm not looking to spend lots of money as I'm a student.

So I'm looking at building a LM3886 amp from chipamp.com. The thing is I'm not looking to spend $40 more than just the pcb for the components to go on it when I can get most at the surplus store down the road for a lot cheaper. So I'm asking if I got a cheap 25w soldering iron (I know how to solder, but I never have on PCB boards) along with this kit, how much trouble is it to learn how to solder these things up? Also is it a good idea to go and try and buy the components for the board separate or should I stick with the kit that includes everything?

My final question is how much power do these amps put out? I'm thinking I'll use these old bookshelf speakers I have till I can make something decent.
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Old 8th November 2007, 02:51 AM   #2
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Hi,
Really, if you're looking for cheap, you're in the wrong place. You could buy a fully functional used receiver, that would meet your needs for a lot less than it will cost to source and build you own. Don't even think about how much time it will take.

The pcb is just the tip of the iceberg. You need a transformer, heatsink and case just to name a few items, each one of these will cost more than the ready to use receiver mentioned above.

We build because we can and enjoy it and like to show-off how smart and capable we are. NOT to save money.
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Old 8th November 2007, 03:13 AM   #3
jcx is online now jcx  United States
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I found a few Accurian amps at my local Radio Shack a couple of weeks ago - just open up the case and move a jumper and you have a stereo amp using the original output RCAs for line in

Radio Shack Accurian Receiver, quality of amp? (pics inside)

$15 for 25 W/ch stereo is worth it for the power supply parts alone, I bought for amusement/hacking value but I have also listened to it - seems up to the quality of the $50 bookshelf speakers I have one driving
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Old 8th November 2007, 01:58 PM   #4
seth556 is offline seth556  United States
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I had looked at the Accurian amp but all the radio shacks around me had none so that won't work.

What I'm looking to do is to build one for me and then another one or two to run some monitors at my church. I'm not too worried about the time it takes. As for the money I can get stuff like cases, transformers, heatsinks, and components for cheap at the electronic surplus store down the road.
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Old 8th November 2007, 02:17 PM   #5
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Does anyone know the voltage rating of the toroid in the Accurion amp?

They have these in stock at my local store and for $15 I might pick some up just for the transformer.

BTW, if you really want to be stingy you don't even need a PCB.
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Old 8th November 2007, 08:38 PM   #6
seth556 is offline seth556  United States
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Instead of buying a kit I'm thinking of just building a p2p lm3875 chipamp. http://diyaudioprojects.com/Chip/P2PLM3875/index.htm


Ok question is does it matter too much what transformer I use as long as it is between 18 and 25vac? I know I'll need dual outputs but can't I just wire up two transformers (one for each side). Because I was thinking about using two of these http://skycraftsurplus.com/index.asp...ROD&ProdID=907 if that doesn't work the place probably has something better in the store.
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Old 8th November 2007, 10:02 PM   #7
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Hi,
You can use two transformers to make a split supply (+/-). They need to be the same, and be careful about wiring them together - they need to be in phase.
The one you linked to doesn't have a high enough VA rating. It should be at least double that (2 amperes). I have used two 60 VA transformers for a single chip amp with good results.
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Old 8th November 2007, 10:05 PM   #8
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Quote:
Originally posted by seth556
Instead of buying a kit I'm thinking of just building a p2p lm3875 chipamp.

Wiring point to point is ok, but you can do better with perf board. Keeps things tidy. Last thing you need is an accidental short.
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Old 9th November 2007, 08:38 AM   #9
seth556 is offline seth556  United States
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Quote:
Originally posted by MJL21193
Hi,
You can use two transformers to make a split supply (+/-). They need to be the same, and be careful about wiring them together - they need to be in phase.
The one you linked to doesn't have a high enough VA rating. It should be at least double that (2 amperes). I have used two 60 VA transformers for a single chip amp with good results.
Where's a good place on-line to get transformers encase I can't find one that meets those specs at the store?

Ok so I think I'll make a few p2p amps since they're cheap to replace if I screw up. Then possibly get some pref boards.
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Old 9th November 2007, 10:26 AM   #10
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Quote:
Originally posted by seth556


Where's a good place on-line to get transformers encase I can't find one that meets those specs at the store?

Ok so I think I'll make a few p2p amps since they're cheap to replace if I screw up. Then possibly get some pref boards.

If you want cheap - stick to the surplus stuff. Retail transformers are not very cheap. Another good (cheap) source of transformers and other usable parts are used amps/receivers.
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