50W Stereo Kit amp runs for 1 min, clips then turns off.

Al600 · 3rd March 2012, 05:26 AM

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?

Puffin · 06:04 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

Did you measure power supply voltages (after bridge rectifier)

are the IC's isolated

are you pushing the amp to the limit

Puffin · 3rd March 2012, 06:10 AM

Quote:

Originally Posted by lanchile

are the IC's isolated

They look like the TF package

lanchile · 06:23 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-

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

Quote:

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)

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

Quote:

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!

3rd March 2012, 06:00 AM	#2
Puffin diyAudio Member Join Date: Feb 2006 Location: U.K	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.

3rd March 2012, 06:12 AM	#5
lanchile diyAudio Member Join Date: Sep 2008 Location: AREA 51	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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3rd March 2012, 06:06 AM	#3
lanchile diyAudio Member Join Date: Sep 2008 Location: AREA 51	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

3rd March 2012, 06:19 AM	#7
Al600 diyAudio Member Join Date: Mar 2012	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.

3rd March 2012, 06:26 AM	#8
lanchile diyAudio Member Join Date: Sep 2008 Location: AREA 51	22uf capacitor on the right is wrong (polarity)

3rd March 2012, 06:32 AM	#9
Al600 diyAudio Member Join Date: Mar 2012	Dude! You're dead right. Let me go and fix it and I'll report back.