smoking caps

KennoMonkey · 7th February 2011, 07:06 PM

I guess it's steam technically. I built a chipamp using the circuit in the datasheet for LM1875, except that the only 50V caps I had for the power to ground filter were 680uF. (Not the power supply, that has four 2200uF caps in two banks of two in parallel). I thought there was a wide tolerance there on the amp board, which is point to point wired perf-board. After a few tests, fixing some cold joints, cleaning up some flux, I finally got the left side to work, but not the right.

I started testing to see if it was the source (an iPod), the speakers, or the amp when I got the funny idea to hook both speakers to one side. I reasoned that hooking them in parallel would result in half the impedance and thus more current, whereas hooking them in series would double the impedance and less current would flow. About 10 seconds after hooking them up in series one of the 680uF caps blew and the other was domed and hot.

Any idea which part of my thought process was at fault?

Thanks
Ken

leadbelly · 7th February 2011, 07:53 PM

Well, I doubt it was anything to do with the speaker, but more likely the caps were wired backwards.

You have to give more detail to really make any progress. Exactly which schematic in the datasheet did you build?

KennoMonkey · 7th February 2011, 08:20 PM

Classic. You nailed it leadbelly.
Thanks, man!
What a dope (me), Ken

7th February 2011, 07:06 PM	#1
KennoMonkey I'm not a monkey diyAudio Member Join Date: Feb 2011	smoking caps I guess it's steam technically. I built a chipamp using the circuit in the datasheet for LM1875, except that the only 50V caps I had for the power to ground filter were 680uF. (Not the power supply, that has four 2200uF caps in two banks of two in parallel). I thought there was a wide tolerance there on the amp board, which is point to point wired perf-board. After a few tests, fixing some cold joints, cleaning up some flux, I finally got the left side to work, but not the right. I started testing to see if it was the source (an iPod), the speakers, or the amp when I got the funny idea to hook both speakers to one side. I reasoned that hooking them in parallel would result in half the impedance and thus more current, whereas hooking them in series would double the impedance and less current would flow. About 10 seconds after hooking them up in series one of the 680uF caps blew and the other was domed and hot. Any idea which part of my thought process was at fault? Thanks Ken

7th February 2011, 07:53 PM	#2
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	Well, I doubt it was anything to do with the speaker, but more likely the caps were wired backwards. You have to give more detail to really make any progress. Exactly which schematic in the datasheet did you build? __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

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7th February 2011, 08:20 PM	#3
KennoMonkey I'm not a monkey diyAudio Member Join Date: Feb 2011	Classic. You nailed it leadbelly. Thanks, man! What a dope (me), Ken