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Old 2nd April 2005, 02:44 PM   #1
DD_Davo is offline DD_Davo  United Kingdom
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Default Amp is intermittent

Hi, i posted about my amp about a month ago with problems regarding it generally not working and the problem seemed to be power, Well i know now it isn't just power. Its the Velleman K4003 i have built and its very intermittent. Once i power it up it tends to work fine for about a minute then the audio disapears and white noise replaces it (like an off-tuned radio station kind of noise) then it all dies.

However i have also found that sometimes before it fully dies the audio looses complete bass and goes very tinny and treble like. I am now very puzzled to what the fault is. Could it be the IC or can any of the capacitors including the electrolytic ones cuase this. The main problem is that it works for a short period of time then cuts out.

If you'd like to see the circuit http://www.velleman.be/Downloads/0/Manual_K4003.pdf there's the link with all the info. The IC is a phillips TDA1521

Thanks for any help you may offer
Dave
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Old 2nd April 2005, 06:21 PM   #2
Nuuk is offline Nuuk  United Kingdom
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Very difficult to say! Check all your solder joints and then check the voltages around the circuit.

How hot does the chip get?
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Old 2nd April 2005, 06:36 PM   #3
Sherman is offline Sherman  United States
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I'm with Nuuk on this one. It sounds as if a bad solder joint is warming up and then breaking contact. I would start checking all solder joints. Start with the ones closest to the chip and work methodically away.

Also as Nuuk said check the voltages around the circuit both at immediate power up (when the amp is working as it should) and then again when it stops working. If you find a significant change (and I think you will) you may be able to locate the bad connection by following the traces.
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Old 2nd April 2005, 06:38 PM   #4
DD_Davo is offline DD_Davo  United Kingdom
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well the solder joints seem fine when checked with a multi meter. The IC running on two Duracell M3's (18V total) gets 'luke' warm. If i use two 1A 12V PSU's it soon gets warm but not overly hot with the heatsink on.

Its a basic circuit anyway. The 4 diodes work as a rectifier for AC current but i'm using DC and they are correctly positioned so power is getting through, then theres the large 4700UF capactiors which i think are to smooth out any AC current then theres the other capactiors and 2 resisitors. Then the IC.

So its not like theres a great deal to go wrong but obviously something isn't right. I;m not sure what effect any other component would have on the amp if damaged (other than the IC)

Thanks for the reply
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Old 2nd April 2005, 06:40 PM   #5
DD_Davo is offline DD_Davo  United Kingdom
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Ah thanks, i didn't see your reply. Well i'll go all over the connections again, when checking voltage it seemed to be pretty close to either the 24V or 18V mark on the input side. I'll re check soldier joints. I suppose it will be that or a faulty component. Thanks
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Old 2nd April 2005, 06:47 PM   #6
Nuuk is offline Nuuk  United Kingdom
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Just to make quite sure - where are you feeding in the DC voltage from the batteries? Is it before or after the rectifier diodes?
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Old 2nd April 2005, 07:01 PM   #7
DD_Davo is offline DD_Davo  United Kingdom
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When i run it on batteries i run it before the rectifier, if you look in the link http://www.velleman.be/Downloads/0/Manual_K4003.pdf last page it shows the circuit diagram, and i feed DC current in before the rectifier. But shouldn't that still work, since the current is travelling through in the correct direction.

I also have rechecked solder joints, and they seem sound

Thanks
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Old 2nd April 2005, 07:11 PM   #8
Nuuk is offline Nuuk  United Kingdom
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I wouldn't put DC into a rectifier bridge. I'm not sure what it would or would not do but I'm sure that it would be better to connect it after the bridge!
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Old 2nd April 2005, 07:40 PM   #9
DD_Davo is offline DD_Davo  United Kingdom
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i shall try that now thanks....

Well i get a lot of popping and crackling when i place the wires after the diodes. Everynow and then i get a 1/10th of a second audio clip but thats it. The crackling is loud though so the amp is amplifying but there is definately a source into the amp as if you bridge the input and output pins audio travels to the speakers without being touched by the amp.
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Old 2nd April 2005, 08:07 PM   #10
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Quote:
Originally posted by Nuuk
I wouldn't put DC into a rectifier bridge. I'm not sure what it would or would not do but I'm sure that it would be better to connect it after the bridge!
Both this Velleman PS (http://www.partsexpress.com/pe/showd...number=320-216) and Tangent's new TREAD PS (http://www.tangentsoft.net/elec/tread/) allow using either AC or DC at the same input before the rectifier.

I don't think DC through a rectifier makes any difference.

-d
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