50W Stereo Kit amp runs for 1 min, clips then turns off. - diyAudio
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Old 3rd March 2012, 05:26 AM   #1
Al600 is offline Al600  Australia
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Default 50W Stereo Kit amp runs for 1 min, clips then turns off.

Hey guys.
I've recently bought and assembled an Altronics K5130 50W Stereo Amp (http://www.altronics.com.au/index.asp?area=item&id=K5130) powered by a 25+25 300VA Toroidal Transformer (http://www.altronics.com.au/index.asp?area=item&id=M5525).
After around 1 minute of run time the amp starts to clip and the sound becomes tinny for around 2 seconds. After this the speakers go quiet. The only way to get sound back is to turn off the amp for around 10-20secs and then the whole process repeats again.
Does anyone have any ideas as to why this is happening?
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Old 3rd March 2012, 06:00 AM   #2
Puffin is offline Puffin  United Kingdom
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The chips will go into protection mode with under or over voltage. Have you measured your power supply? Is it split rail or single supply?

EDIT: I have just looked at the Power Supply schematic you have photographed. This shows a supply of + / - 15v using voltage regs. The LM3886 needs at least +/-28v.

Last edited by Puffin; 3rd March 2012 at 06:04 AM.
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Old 3rd March 2012, 06:06 AM   #3
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How many ohms are the speakers
Did you measure power supply voltages (after bridge rectifier)
are the IC's isolated
are you pushing the amp to the limit
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Old 3rd March 2012, 06:10 AM   #4
Puffin is offline Puffin  United Kingdom
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Quote:
Originally Posted by lanchile View Post
are the IC's isolated
They look like the TF package
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Old 3rd March 2012, 06:12 AM   #5
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Correct me if I am wrong here, but I see the green wire going to the wrong voltage. one is V+ (from cap) and the other side goes to V-
one wire should be V- and the other V+...
ok I guess the voltage is good ...But if you see the smallest cap on the right...IT IS WRONG!!!!

Last edited by lanchile; 3rd March 2012 at 06:23 AM.
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Old 3rd March 2012, 06:14 AM   #6
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Quote:
Originally Posted by Puffin View Post
They look like the TF package
Got it, Thanks!
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Old 3rd March 2012, 06:19 AM   #7
Al600 is offline Al600  Australia
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I've measured the transformer output, the rails and the source voltage. Even after the amp stops producing sound, these values are all withing the values stated in the manual. It seems that some componant may be overheating but the power transistors are luke warm at most. 15V is only used if a pre-amp is to be connected. The rails are running at around 37V. Hope this helps.
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Old 3rd March 2012, 06:26 AM   #8
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22uf capacitor on the right is wrong (polarity)
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Old 3rd March 2012, 06:32 AM   #9
Al600 is offline Al600  Australia
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Dude! You're dead right. Let me go and fix it and I'll report back.
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Old 3rd March 2012, 06:41 AM   #10
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Quote:
Originally Posted by Al600 View Post
Dude! You're dead right. Let me go and fix it and I'll report back.
well, sometimes we rush too much to finish our projects that we do not pay attention to these things. We all make mistakes!
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