Hi Tai -

You've probably already checked the simple stuff, but sometimes thats what
will bite you.  Did you lay out the circuit board yourself?  Have you
checked the output of the power supply with a meter AC and DC...  have you
looked at it with a scope?

-  Remember the 7912 has a different pinout that the 7812 - Ground is not
on the middle on the 7912.
-  Have you checked the continuity and orientation of the diodes.
-  Is it a new transformer?  Have you checked it's output?
-  Have you checked the orientation of the caps?
-  Where is the audio portion of the circuit grounded?  If your op-amps use
+/- 12 volts is the circuit properly referenced to ground?

I hope this is helpful...   so please don't be offended.   Good luck.

-  Robert

>Hi 2 All
>
>Attach a quick schematic that I draw to explain my problem.
>The problem is a hum I can't rid of.
>I try to increase the 1000uf capacitors with larger ones (4700uf) but no
>change, only the hum sound changed to lower. I try to increase the output
>caps' from 100uf to 470uf but no change at all.
>what I can do more? maybe the bulky transformer that on the pcb can cause
>this hum problem?
>
>if you think the component placement is important I can send the pcb
>picture/drawing (even I put it in the way that unregulated / unfiltered
>traces will not be near the audio circuit)
>
>I really need your help!
>
>Tal
>
>Attachment converted: Blue Main:psu+-12.jpg (JPEG/JVWR) (0007FE5A)

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics