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Old 2nd June 2011, 03:21 AM   #1
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Default lm3886 help needed

I have modified a CT EI 18-0-18 into 2x24 dual secondary got around 29 v to 33v according to the ac mains supply.I use carlos snubberised unregulated psu.My Lm3886 is not producing any sound.Have tried various circuit but still same thing like it gets extremely hot,around 0.4v at the output .Do I really need a torroid or regulated psu.I can power an old 3055 amp from this psu but not lm3886 .Plz help me out .thanks.
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Old 2nd June 2011, 04:17 AM   #2
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Sounds like the chip is bad.
If it is getting that hot I am asuming that it is mount to a heatsink.
Yes there are some 2N3055 designs that will work on that range of voltages.

jer
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Old 2nd June 2011, 08:16 AM   #3
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Quote:
Originally Posted by simply14prem View Post
I can power an old 3055 amp from this psu but not lm3886
This tells you that the power supply works, and the problem is most likely somewhere else. Check how you've connected the 3886 and see if you haven't done anything wrong there. Once you've established that your circuitry is absolutely faultless and it still doesn't work, only then try exchanging the 3886 for a new part to see if the first one was accidentally blown up somewhere along the line.
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Old 2nd June 2011, 09:24 AM   #4
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Hi if you could post the schematic and some build pics that would help. Have you got the mute circuit (unlikely to be the problem if the chip is getting hot, but I always ask).

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Old 2nd June 2011, 02:16 PM   #5
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I don't know how to draw the circuit but it is very close to the one in chip amp.
I put zobel, plus 1k at the input. for mute I have tried 10k ,33k,22k .I have tried 3 lm3886 chips,but still probs persist.I have tried few heat sinks around double times I use for tda 2040 .I have connected power supply for a couple of chips like 4xTl072 plus one tda 2040 after regulation from the psu.All other chips are working.The voltage after load is around 27/26v .Is this too low?Or may be the chip is a duplicate bad chip.Also I number the chips legs as 1 from my left side when the chip faces me. Am I right.?

Last edited by simply14prem; 2nd June 2011 at 02:41 PM.
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Old 3rd June 2011, 03:05 AM   #6
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27V should be fine (that is what I run my LM3886 on) and yes pin 1 is the left most when looking at the front of the chip (with legs facing downward).

I suspect that your problem is not power-supply related and will ask this thread to be moved to the chipamps forum.

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