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Chip Amps Amplifiers based on integrated circuits

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Old 21st June 2012, 07:10 PM   #111
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Hello apexaudio!
I really appreciate all your work and research.
Thanks for posting your work on this forum!!

I have built this module according to your PCB and installed the correct parts on it.
The PSU is 24-0-24V/5A Trafo with 4700uF/50V Capacitors 85 degree types.
When I try to power up the circuit, there is only hum from the speakers... I am using the amp on a 8 ohm load.
I also checked for shorted PCB traces. But everything is fine.
I have used metal film resistors and box type capacitors for the build to induce the least noise.
But this is something else...! The IC gets hot as soon as I switch the amp on.
Is it that there are shorted traces? Or the IC is bad?

Regards
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Old 21st June 2012, 07:13 PM   #112
udailey is offline udailey  United States
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The back of the IC can not touch metal if that metal is grounded. If you have insulated the back of the chip then you need to also make sure that there is no bolt touching the tab of the chip. Turn it off and use your multimeter to see if you have any resistance/short between ground and chip tab.
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Old 21st June 2012, 07:17 PM   #113
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Quote:
Originally Posted by udailey View Post
The back of the IC can not touch metal if that metal is grounded. If you have insulated the back of the chip then you need to also make sure that there is no bolt touching the tab of the chip. Turn it off and use your multimeter to see if you have any resistance/short between ground and chip tab.
My IC is a full plastic one..
It does not have a tab!

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Old 21st June 2012, 08:41 PM   #114
udailey is offline udailey  United States
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Then get a wire and put an alligator clip on each end. Attach one end to earth ground and the other end should then touch signal ground, then speaker ground, then the 0V ground from the secondary side of the transformers. Listen while you do this. Often if its not a cold solder joint you can find the grounding problem this way. Also try one alligator on signal ground then touch all the other grounds then try one alligator 0V and one Earth.
Uriah
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Old 22nd June 2012, 06:09 AM   #115
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Tried doing that too....But there is no change in the output....only hum...And the IC gets really very hot within 3-4 seconds...I think thats a bad IC....
What say guys?
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Old 22nd June 2012, 12:39 PM   #116
AndrewT is online now AndrewT  Scotland
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Para,
did you test the wiring of your transformer?
Did you test your PSU?
Did you test the amplifier for output offset?
Did you just connect everything up to your speaker and hope for the best/worst?
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Old 22nd June 2012, 02:06 PM   #117
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Quote:
Originally Posted by AndrewT View Post
Para,
did you test the wiring of your transformer?
Did you test your PSU?
Did you test the amplifier for output offset?
Did you just connect everything up to your speaker and hope for the best/worst?
The transformer wiring seems to be fine according to me.
The signal ground, transformer's middle wire (ground) and the amplifier ground are soldered to each other.
I use a 35A Bridge. The power supply seems to be fine too.
I am just scared to check the DC Offset!! The IC turns so very hot as soon as it is connected even though it is on an heatsink! I just expect that it will burn!
So I'm kinda scared too!!

I still don't know what the problem is! I also checked for shorted traces.
But I din't find any!

I'm confused!!
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Old 22nd June 2012, 02:08 PM   #118
AndrewT is online now AndrewT  Scotland
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Looks like you are saying that you just banged it all together and hoped for the worst, "because it looked right" !!!!!
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Old 22nd June 2012, 02:08 PM   #119
udailey is offline udailey  United States
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Time for pictures.
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Old 22nd June 2012, 06:13 PM   #120
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Quote:
Originally Posted by AndrewT View Post
Looks like you are saying that you just banged it all together and hoped for the worst, "because it looked right" !!!!!
Quote:
Originally Posted by udailey View Post
Time for pictures.
The Layout of components does not match the schematic.
D2 has to be reversed on the component layout for it to match!
I realized it when I tried to troubleshoot the PCB to find any mismatch in traces and the schematic...

The amp's working smoothly once i reversed the diode!
Also I changed the 15K resistor to 33K to increase the gain...

Thanks for all your help guys!

Regards!
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