I recently "finished" building an LM3886 amplifier from Chipamp.com. I have it currently hooked up using a 22v transformer, so after it is rectified to DC power it is about +/-30v. One of the boards is working great, I believe. I can only leave it on for about 5 seconds, so I couldn't do much testing. But on to my problem, the other board.
On the second board, the chip gets hot. It gets noticeably hot in about 5 seconds, and too hot to touch in about 10. This happens exactly the same regardless of if there is input, no input, speakers connected, or no speakers. If I connect speakers, it plays music, but with a terrible buzzing/crackling noise (sounds much worse and different than I imagine ground loop hum would be). For a while you could hear a hum from the board itself, although I could not tell which component specifically, and it has since stopped. One of the rectifiers gets a little warm, and the transformer is heating up too, more than what I think is normal. The chips are attached to a heat sink, but my thermal paste has not come yet. I understand that these chips can get hot when not cooled properly, but this seems excessive. Does anybody have any idea what the problem could be, or what I should check next?
Thanks for all your help! Remember, this is my first build, and I'm a beginner, so please keep the replies somewhat simple, stuff I can understand.
On the second board, the chip gets hot. It gets noticeably hot in about 5 seconds, and too hot to touch in about 10. This happens exactly the same regardless of if there is input, no input, speakers connected, or no speakers. If I connect speakers, it plays music, but with a terrible buzzing/crackling noise (sounds much worse and different than I imagine ground loop hum would be). For a while you could hear a hum from the board itself, although I could not tell which component specifically, and it has since stopped. One of the rectifiers gets a little warm, and the transformer is heating up too, more than what I think is normal. The chips are attached to a heat sink, but my thermal paste has not come yet. I understand that these chips can get hot when not cooled properly, but this seems excessive. Does anybody have any idea what the problem could be, or what I should check next?
Thanks for all your help! Remember, this is my first build, and I'm a beginner, so please keep the replies somewhat simple, stuff I can understand.
None, yet. But it still shouldn't get that hot in a matter of seconds, I don't think. I will post pics tonight, when I'm home from work.
Guys the chips are the insulated ones so there was no need for insulators between the chips and heat sink.
I helped bryce put this amp together and we DO have a heat sink in it, but we were out of thermal paste so there is none between the chip and heat sink which I under stand is not good. We have a parts express order coming in this week with paste and will add it right away. The heat sink was however filled flat so there is good contact with the chip and aluminum. I wouldn't think the chips would heat up that fast when not powering anything. My chip amp runs really cool at low volume and only gets warm at full volume.
The transformer he is using is 22 + 22 volts but only 25va which will get up graded in the future to 200va.
He said both the bridge rectifiers are getting hot as well as the transformer which makes me thing you guys are onto something with the oscillation. We put the amp together at my house and I tested it for just a moment (since we didn't have thermal paste) and all was well. The amp was sent home with Bryce so he could add proper input and output jacks and then the problems showed up. Ether something changed after it left my house, or I didn't test it long enough to see the problems which is very possible because I didn't test it for very long.
Perhaps Bryce can post some pictures of his amp so you guys can get a better look. Please keep in mind he was going for a "steam punk" look and the case is a little rough : )
Dale P.
I helped bryce put this amp together and we DO have a heat sink in it, but we were out of thermal paste so there is none between the chip and heat sink which I under stand is not good. We have a parts express order coming in this week with paste and will add it right away. The heat sink was however filled flat so there is good contact with the chip and aluminum. I wouldn't think the chips would heat up that fast when not powering anything. My chip amp runs really cool at low volume and only gets warm at full volume.
The transformer he is using is 22 + 22 volts but only 25va which will get up graded in the future to 200va.
He said both the bridge rectifiers are getting hot as well as the transformer which makes me thing you guys are onto something with the oscillation. We put the amp together at my house and I tested it for just a moment (since we didn't have thermal paste) and all was well. The amp was sent home with Bryce so he could add proper input and output jacks and then the problems showed up. Ether something changed after it left my house, or I didn't test it long enough to see the problems which is very possible because I didn't test it for very long.
Perhaps Bryce can post some pictures of his amp so you guys can get a better look. Please keep in mind he was going for a "steam punk" look and the case is a little rough : )
Dale P.
Looking at some posts about oscillation I wonder about the length of our speaker wires. They are quite long and run from one side of the case to the other.
You guys mentioned an output zobel net work. would something like this picture help or it this already built into the chip amp board?
Dale P.
You guys mentioned an output zobel net work. would something like this picture help or it this already built into the chip amp board?
Dale P.
Attachments
Just the board, not parts. Dale (ibuildstuff4u) built his with the same exact parts though, and they work, so they are correct components.
No we built the power supply our self, but my amp has the same design and it works fine. My nephew soldered up the boards, but I gave them a good look and they seem fine. I guess we will have to go over them again and re check.
The boards are from chip amp and the parts are from mouser, but I have the same set up and again it is working just fine. I ran mine for 6 hours yesterday and it ran good. I even put a 29v + 29V transformer in mine for a while and it did very well and only got warm when pushed really hard. I could up the heat sink size and leave the larger transformer in, but I didn't see much gain so I put my 18v + 18V back in.
This is the power supply circuit we used but shortened it up and only have two caps per channel instead of four.
Dale P.
The boards are from chip amp and the parts are from mouser, but I have the same set up and again it is working just fine. I ran mine for 6 hours yesterday and it ran good. I even put a 29v + 29V transformer in mine for a while and it did very well and only got warm when pushed really hard. I could up the heat sink size and leave the larger transformer in, but I didn't see much gain so I put my 18v + 18V back in.
This is the power supply circuit we used but shortened it up and only have two caps per channel instead of four.
Dale P.
This afternoon I want to test a few more things on the amp, but immediately found a new/different problem. Before I went to pull the boards, I did one last check of the voltages. With both boards connected, I was getting about +22v or +23v on the positive side (I'm going off of memory). I was getting about -9v on the negative side. Curious, I disconnected the boards, and tested the voltage coming off the supply- and now I'm getting no voltage. I could follow the voltage all the way up to the bridge rectifiers, then lost it, so I figured they must be bad. I pulled them both off, and sure enough, the were both bad (I got no continuity across any of the pins, either direction). What would cause them to stop working? Especially both of them? I just want to see if I can find the reason before I go throwing new ones at it. They were rated for 400v, 4a, so it definitely was not too much power.
Also, I FINALLY took some pictures. But for whatever reason, it won't let me post them. I'll send them to my uncle tonight, and see if he has better luck.
Also, I FINALLY took some pictures. But for whatever reason, it won't let me post them. I'll send them to my uncle tonight, and see if he has better luck.
I'll mail them. I know how to, it would load them then say I had a "missing security token" or something like that.
Alright, when I replace them I'll go 10 amp. Do you mind explaining your reasoning? I'm sure there is way more to it than I am thinking, I had figured as long as it was above the rating of my transformer I was fine.
So I think I found a new transformer. It is a dual 24v, 160VA.
Here is the link:
miscellaneous.html
I know the voltage is a little high, and the amperage is a little low, but really the $22 is all I'm willing to spend, and it's the best I can find at that price. Also, there are other items I want from apexjr anyways, so shipping cost isn't an issue.
So, would this be "good enough" for now? Keep in mind what it currently has is a tiny 22v, 25VA.
Here is the link:
miscellaneous.html
I know the voltage is a little high, and the amperage is a little low, but really the $22 is all I'm willing to spend, and it's the best I can find at that price. Also, there are other items I want from apexjr anyways, so shipping cost isn't an issue.
So, would this be "good enough" for now? Keep in mind what it currently has is a tiny 22v, 25VA.
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