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Al600 3rd March 2012 05:26 AM

50W Stereo Kit amp runs for 1 min, clips then turns off.
5 Attachment(s)
Hey guys.
I've recently bought and assembled an Altronics K5130 50W Stereo Amp ( powered by a 25+25 300VA Toroidal Transformer (
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?

Puffin 3rd March 2012 06:00 AM

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.

lanchile 3rd March 2012 06:06 AM

How many ohms are the speakers:confused:
Did you measure power supply voltages (after bridge rectifier):confused:
are the IC's isolated:confused:
are you pushing the amp to the limit:confused:

Puffin 3rd March 2012 06:10 AM


Originally Posted by lanchile (
are the IC's isolated:confused:

They look like the TF package :)

lanchile 3rd March 2012 06:12 AM

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-:eek:
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!!!!

lanchile 3rd March 2012 06:14 AM


Originally Posted by Puffin (
They look like the TF package :)

Got it, Thanks!

Al600 3rd March 2012 06:19 AM

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.

lanchile 3rd March 2012 06:26 AM

22uf capacitor on the right is wrong (polarity):eek::eek::eek::eek::eek:

Al600 3rd March 2012 06:32 AM

Dude! You're dead right. Let me go and fix it and I'll report back.

lanchile 3rd March 2012 06:41 AM


Originally Posted by Al600 (
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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