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PostPosted: 07 Nov 2008, 18:30 
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Joined: 28 May 2008, 21:53
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Great stuff! I'm glad it worked out for you. Looking forward to the pictures.

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PostPosted: 12 Nov 2008, 21:41 
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Joined: 10 Sep 2008, 19:54
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Location: Boston
Actually i've had a bad turn of events!

The one finished unit worked great when I tested it outside my project box, but once I mounted it and wired it to the input/output jacks, I got nothing. There is a +5V rail for the turn on logic that would give me voltage, but when I connected it to the mute/sleep lines (+5V is awake and un-muted) I got nothing.

In testing the unit to see what was wrong i ended up burning the chip! It actually caught fire!

I had ordered another kit to replace the first dead unit, and I assembled that yesterday and again it worked before I connected the wires, but not afterward. I have a metal project box and I mounted the unit in the box (on the metal screws) to be sure there were no issues with connecting the mounting holes together (there were none, it worked fine).

I swear that the cause of the issue has to be soldering the wires to the board for input/output. But that makes no sense! I got frustrated and gave up (for fear of setting another chip on fire) but I really would like to know what went wrong! IT makes no sense that a working unit would stop working just because I soldered some (unconnected) wires to the board.

any thoughts?


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PostPosted: 12 Nov 2008, 22:35 
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Joined: 06 Jun 2008, 20:12
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Location: Houston, TX
Yes.
Your ground from the RCAs or some other input/output is not insulated from the chassis. Then your chassis is connected to your heatsink. Then your heatsink is connected to your chip. Then, well you have grounded the back of the chip which, and I may be wrong but I think I am right, is also Negative :) :(
There is a great site on building these things by Mick Feurbacher. Dogbreath.de or something. Just a sec....
http://dogbreath.de/Chipamps/ThreeResAm ... esAmp.html
He has lots of other chip amp projects that basically vary in the number of resistors or caps he uses. Anyway. If you build just like this... it will work. But you have to have the TF chip or you have to use mica or poly-somethingorother to insulate it from your heatsink/chassis.
Sorry to hear you smoked it man. If you go to www.apexjr.com you can get more for $3.50. Just remember I dont think his are TF so you have to insulate it yourself. You can get mica pads on ebay or mica sheets at www.allelectronics.com.
Ri

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PostPosted: 12 Nov 2008, 22:54 
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Ri, this is a AMP9 kit he is working with.

Since it worked fine out of the enclosure this has to be some sort of grounding problem as mentioned. My AMP6 did not need to be isolated from the heatsink/chassis but check what the manual says about the AMP9.

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PostPosted: 13 Nov 2008, 08:31 
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Ugh. Sorry about that. For some reason I just assumed it was LM3886.
You might want to read pages 14 and 15 of the datasheet for your chip. There are a lot of warnings about wrong voltage and grounding schemes. Anyway, I am betting that somehow you have - or + crossed to your ground somewhere. The input section can only handle 5V and if your RCA somehow got one of the rails crossed to it then this would be more than it could handle. ALSO there is talk about the chip heating up really fast on the 41Hz forums. For instance http://www.41hz.com/forums/topic.asp?TOPIC_ID=2126
Ri

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PostPosted: 24 Nov 2008, 19:54 
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Location: Boston
I brought the unit out again to test it and, again, made sparks and smelt burning. There is some black-ness coming out of the bottom of the chip on the leads.

I think these units should be fine but for bad chips, but the chips have many pins and i'm skeptical about removing/replacing them. Plus they're $30-something from 41hz.com. Think I can salvage this project by buying some new chips? I'm pretty sure the only issue with both units was that I installed them to a conductive box. That shouldn't have damaged any of the other parts, should it?


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PostPosted: 24 Nov 2008, 23:31 
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It is tough to say. When there is a short, a number of things can happen. So you seen any other physical damage?

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