Problems with LM3887 amp ic's help!! - diyAudio
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Old 12th May 2001, 03:45 PM   #1
diyAudio Member
 
Join Date: May 2001
Location: Denmark
I have build THe 56 W amp from the ESP projeckt page
using the lm 3887 power ic, I make up the circuit board my self and I have Check it maney time, But there is still a problem with it.
I give feed the amp with +-37 v stabil 8000uf cap. power supply. The amp is playing. and it sound well. But when i messure at the output there is a low dc volgete witch swing between -4 to+ 4 volt. and the chip gets veryu hot when it is at the peak dc. It is very sad because I realy don't know why it is doing like this the bypass cap (100n) is very close to the ic.

If any one have build this or know what can be the problen plese let me know.
jeppe cohrt denmark.
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Old 12th May 2001, 05:07 PM   #2
Geoff is offline Geoff  United Kingdom
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Join Date: Apr 2001
Location: UK
Jeppe

I assume you are referring to the LM3886 (National Semiconductors don't make a 3887).

Though generally the pin-out of the LM3886 is the same as that for the LM3876, there is one important difference, pin 5 must be connected to the +ve supply rail, whereas on the LM3876 it can be left open circuit.

Connecting pin 5 to the positive supply rail should cure your problem. I will ask Rod Elliott to amend his poject page accordingly.

Geoff
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Old 27th May 2001, 04:35 PM   #3
Geoff is offline Geoff  United Kingdom
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Join Date: Apr 2001
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Jeppe

Did my suggestion solve your problem? It's useful to get some feedback on things like this so as to know that correct advice is being provided.

You might also find that you get more response to other postings if you acknowledge any help that has been given previously.

Geoff
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Old 27th May 2001, 05:08 PM   #4
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Join Date: May 2001
Location: Denmark
Default I haven't solve the problem

I Have both some lm 3886 and some lm3876 and I already had cornect pin 5.
Im afraid that I have damage the chip. What about the pin that are not uset?

Is the circuit that linkwits made for lm3886 better?

I make up a stereo amp using lm1876 and it play very well.

When I have make the amp using lm3886 I think I will try to find out how to use them in parellel if it posible. to make a more powerfull amp that way.

jeppe c.
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