Problem with LM4780

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Dielkius

Member
Joined 2005
Hello,

I have a problem,
I found circuit in this forum:
www.e-ideja.com/dielkius/schematic.gif

And I made PCB for that:
www.e-ideja.com/dielkius/pcb.jpg
www.e-ideja.com/dielkius/pcb2.jpg

And there is a part schematic:
www.e-ideja.com/dielkius/parts.jpg

I have 2 transformers, one 33-0-33 and one 15-0-15 (there is values after diode bridges). I connected +33 G -33 then I conected +15 -15 and that transformer ground connected with PCB ground.

And a problem: When I turn it on nothing happens, LM's get warm, but speaker silent, no buzzz or etc. Whats wrong? Maybe you can help me..
 
Juergen Knoop

Juergen Knoop

Member
Joined 2007
probably impossible to tell you what went wrong.
It needs some troubleshooting with scope, signal generator and so on
at least there is one design error on the schematic...
a bias resistor at U4 is missing, you could try 47k from pin 3 to ground.
without a path for the bias current the operational amplifier could latch up. Maybe thats just your problem.
 
D

Dielkius

Member
Joined 2005
Second transformer is for bufer and driver (OPA134 and DRV134) I don't use that part of schematic where is LM317 and LM337, I use another transformer to power up that two micro's.. Now i'm going to try put resistro 47k...

Thank you juergenk,
And sorry for my bad english ;)
 
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