Problem with LM4780

Dielkius · 12th January 2007, 05:11 PM

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 · 12th January 2007, 05:40 PM

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.

Juergen Knoop · 12th January 2007, 06:09 PM

btw. are the inputs of U5/U6 shorted?

Quote:

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.

why a second transformer?
Regards
Juergen

Dielkius · 12th January 2007, 08:32 PM

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

Dielkius · 12th January 2007, 08:32 PM

Nop, 47k resistor not help...

halo0925 · 12th January 2007, 10:24 PM

Check your mute pins if the mute is alright bypass the ins on the 4780 inject the signal there without the buffer and DRV134

Dielkius · 13th January 2007, 09:14 AM

Hi halo0925,

Thank you for reply, i tryed to put signal without bufer and driver, first to one LM and it worked, and then to another LM, and it worked too..

So problem is driver or bufer..yes?

AndrewT · 13th January 2007, 12:47 PM

Hi,
I thought chipamps needed decoupling (electro + film/ceramic) right at the supply pins. Neither of these parallel pairs have any local decoupling.

Dielkius · 13th January 2007, 01:06 PM

I take another schematic without buffer, just driver (DRV134) and everything works OK..need another buffer, and new PCB

12th January 2007, 05:11 PM	#1
Dielkius diyAudio Member Join Date: Nov 2005 Location: ---	Problem with LM4780 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..

12th January 2007, 10:24 PM	#6
halo0925 diyAudio Member Join Date: Aug 2006	LM4780 Check your mute pins if the mute is alright bypass the ins on the 4780 inject the signal there without the buffer and DRV134

13th January 2007, 12:47 PM	#8
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, I thought chipamps needed decoupling (electro + film/ceramic) right at the supply pins. Neither of these parallel pairs have any local decoupling. __________________ regards Andrew T.

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12th January 2007, 05:40 PM	#2
Juergen Knoop diyAudio Member Join Date: Jan 2007 Blog Entries: 3	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.

12th January 2007, 08:32 PM	#4
Dielkius diyAudio Member Join Date: Nov 2005 Location: ---	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

13th January 2007, 09:14 AM	#7
Dielkius diyAudio Member Join Date: Nov 2005 Location: ---	Hi halo0925, Thank you for reply, i tryed to put signal without bufer and driver, first to one LM and it worked, and then to another LM, and it worked too.. So problem is driver or bufer..yes?

13th January 2007, 01:06 PM	#9
Dielkius diyAudio Member Join Date: Nov 2005 Location: ---	I take another schematic without buffer, just driver (DRV134) and everything works OK..need another buffer, and new PCB

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