Was wondering if you received my last post. Where is your star point ground? The pcb drawing you just sent shows the worst case senario for grounding. The two 1000uf cap grounds are as far apart as you could make it. Why? Your ground return(s) on the regulator(s) go to the caps and share a common ground back to the transformer. All your grounds are sharing other grounds making it back to the star point ground. Think of your heavy ground traces as being 10 ohm resistors back to the transformer and you will see what I mean. To improve your layout, rotate your 1000uf caps with the hot sides pointing toward your opamp. Run your cap grounds together and make the center of that point your star point. Run the transformer common through the bridge ac pins to the star point. With as much current as you are consuming, your heavy traces don't have to be as wide as they are now. You don't really need the two 10U (10uf) caps near your regulators. Put those as close to your opamp power leads along with your U10 caps (.1uf) as possible. The common ground from these caps MUST go directly back to the star point between your bridge +/- without touching any other ground return. All your signal grounds can then be tied to the common ground of the opamp caps. Your hum will go away. Rick Tal Bejerano - AMC wrote: > To All > > I draw the pcb again :-) > > please give me your advice. > > Regards > > Tal Bejerano > AMC - ISRAEL > > -----Original Message----- > From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On > Behalf Of Stuart O'Reilly > Sent: Monday, June 24, 2002 8:12 AM > To: PICLIST@MITVMA.MIT.EDU > Subject: [EE]: Hum problem- draw it again > > >From where I stand it looks like you have your -9 volt regulator connected > incorrectly. You have it connected as 1 in, 2 gnd and 3 out. It should be 1 > gnd, 2 in and 3 out. It's > pinout is different to a positive voltage regulator. > Regards > Stuart > > 24/06/02 9:48:14 AM, Tal Bejerano - AMC wrote: > > >I draw again the PSU section. can you tell if all grounds ok? > >I didn't put all components (OPamp and it components) in place, cause I > need > >to know if the PSU is ok in this position. > >next, if it's ok, where I should connect the ground to the preamp? to the > >same 0V point? > >mind that I didn't connect the PSU's output caps yet. > >furthermore, do you think I need mains ground? > > > > > >Regards > > > >Tal Bejerano > >AMC - ISRAEL > > > > > >-----Original Message----- > >From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On > >Behalf Of Herbert Graf > >Sent: Sunday, June 23, 2002 9:13 PM > >To: PICLIST@MITVMA.MIT.EDU > >Subject: Re: [EE]: Hum problem > > > > > >> >I don't have a scope so I cant see what is going on, don't be offended I > >> >have to work "blind in the dark". > >> > >> Tal, it looks like you are just like me, "in development" ;o) > >> > >> I have a tip, that may or may not work for your problem > >> > >> Use a common speaker, with a resistor in series, in the > >> output of your power supply > >> > >> If you have ripple in your PSU, it can (or not) be > >> determined with this simple hack > >> > >> In my pinball repair times, when there wasn't a scope > >> avaiable (always), this was something that could find a shorted > >> diode or a dried cap on the psu. Dunno if it will be of use to > >> you, but here it is anyways ;o) > > > > Interesting trick. A trick I have used is to hook up a true RMS > >meter to > >the DC line, if there is ripple it shows up on the meter. It's not super > >accurate but it gives a qualitative result (ie. there is more ripple then > >before). TTYL > > > >-- > >http://www.piclist.com hint: The PICList is archived three different > >ways. See http://www.piclist.com/#archives for details. > > > > > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > ------------------------------------------------------------------------ > Name: psuII.jpg > psuII.jpg Type: JPEG Image (image/jpeg) > Encoding: base64 -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body