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Old 22nd July 2015, 07:46 AM   #1
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Default Crackling noise lm1875 amp

Greetings to everyone.

This is my first post in this forum, although i' ve been following it for a long time.

Recently I' ve finished my first serious diy project, a lm1875 based gainclone chipamp. Two amplifier boards made on stripboard (layout found somewhere in this forum), on transformer and suitable psu. I was amazed as everything fired up nicely, with better sound compared to my 2 commercial amplifiers.

All parts where mounted in an open wooden box as I wanted to swap different values for the components, just to see what improvements i could get.

As soon as I found what i liked most, I thought that it was time to move the amplifier to a closed, permanent wooden box.

After I had checked everything (or at least i thought that i did) i plugged in the power chord to the wall mains and i had a short circuit (I don't know the word, the fuse for the main electricity went down). I checked again, and found a forgotten ground cable from one board was loose and i supposed that it touched something it wasn't supposed to.

I fixed it, fired the amplifier again and this time only on channel came up, meaning that music was playing only from one loudspeaker. I did some swapping to see if the problem was in the speaker or not and i found that it was on one amplifier board, which keeps giving me the following sound:

popping

In case the above link is not working, the sound is a periodic one, like a waveform and the power led flashes silmutanuasly with the sound.

Just two images from my finished amplifier, the "broken" board is the right one.

https://drive.google.com/open?id=0B6...3lja2h6azlrdVk
https://drive.google.com/open?id=0B6...25uUnVteU5lZXc

Could it be a fried lm1875, or a grounding issue? Any ideas and suggestions would be helpful.
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Old 22nd July 2015, 02:21 PM   #2
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Your files will not open for me, it is saying I need permissions.

John
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Old 22nd July 2015, 02:53 PM   #3
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check the board again, and if no issued found swap the ic for a new one.
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Old 22nd July 2015, 07:35 PM   #4
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Wiggle test.
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Old 22nd July 2015, 08:09 PM   #5
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Quote:
Originally Posted by john blackburn View Post
Your files will not open for me, it is saying I need permissions.

John
Sorry for this John, I didn't know how to upload an audio file so I linked it to my google drive, hoping that anyone would have access to it. I' ve shared the file with you so hopefully you should be able to listen to it. If you know how to upload a music file here, please let me know.

Quote:
Originally Posted by Arty View Post
check the board again, and if no issued found swap the ic for a new one.
I checked the board, everything seems ok, I used a multimeter for continuity test and everything seems fine. I was ready to desolder the chip that is working and swap it with the damaged one to see if the board is working, but I did not want to risk the chip['s pins to break.

Do you think I could use a tda2050 as it is cheaper and much easier for me to find?

Quote:
Originally Posted by Fast Eddie D View Post
Wiggle test.
Is it necessary cince every connection is tested in continuity mode and seem ok?
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Old 22nd July 2015, 10:02 PM   #6
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Quote:
Originally Posted by yianemma View Post
Is it necessary cince every connection is tested in continuity mode and seem ok?
It should be part of the continuity test. I've been down this road many times before.

Have you measured voltages at the chip pins? I always power up a new circuit with series resistors in the supply legs, or else I use a 9 volt battery, before I power it up full power. Then I do a voltage test. Powering up a newly constructed circuit with full power can fry a chip if there's a problem with the assembly.
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Old 22nd July 2015, 10:08 PM   #7
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i suggest to not even consider tda2030/2040/2050 chips at all, as most of them are fakes.
i suggest ordering lm1875 directly from manufacturer.

lift one leg of passive components and check for values.
check the supply voltage too.

most probably the chip is all the way dead, but other components may got hurt too.
testing a component that is in a circuit can mislead.
that is why 1 leg has to be lifted for resistors/caps/diodes/etc...
so you can verify everything is awwwwright.
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Old 23rd July 2015, 06:33 AM   #8
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I couldn't resist and i used my working lm1875 chip to test the "broken" board. Good news is that both chips are ok, but something is wrong with the board.

I'll make a new one with new components as soon as i' ll get them.

Or maybe I' ll use the working board on my guitar amp and go for a tpa3116, as it is getting good reviews, or maybe a ready one lm1875 board from ebay.
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Old 24th July 2015, 05:52 AM   #9
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dunno man, if i went over the trouble of building them i would not give up on them.
there isin't that many components to make an 1875 amp, and you say the ic is good.
check the rest, it should not be all that difficult.
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Old 25th July 2015, 03:40 PM   #10
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You are absolutely right, and that i am planning to do some testing as soon as i get home. But i will order a tpa 3116 just for fun.
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