LM3875 Gainclone Not Working and Stuck to Rail ...

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dannyjmf

dannyjmf

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Joined 2010
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Hi ...

Today just build a gainclone LM3875 amplifier and found that it is not working ... output stuck to rail ... the circuit i used is i followed from the NS datasheet ...

BTW , i found that in the feedback path there is a capacitor in the schematic By NS. But i refer to some of the DIY projects schematics they are not included ... is it the cause of my problem ... ?

I need serious help here ... any feedback and suggestions are much appreciated and welcomed ...
 
DUG

DUG

Member
Joined 2003
Fig 1 or Fig 3?
 

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JMFahey

JMFahey

Member
Joined 2009
Ok.
Measure and post voltage on all 5 legs shown (1/3/4/7/8)
Measure from PS ground to each leg, straight at the chip.
Be careful not to let the multimeter tip slip and short to another leg.

By the way: I hope the chip is mounted to a heatsink and that you insulated it with mica+grease (and a screw-insulating nipple if needed).
Also, with power off, measure resistance to ground from leg 4 .
 
dannyjmf

dannyjmf

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Joined 2010
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Hi everyone....
I have supply voltage of +-35V...
And i have +35V coming from output!!!!
How the hell is that possible?
Click to expand...

Do you had the star grounding of the amp connected? if not likely the problem ... and be sure to include the Ci(optional capacitor) as well ... last time i also had the same problem with my gainclone LM3875 ... hopes this helps ...

good luck
 
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