Yes and No. Mains ground can be tied to your chassis as ground for shielding,
but your power supply ground and application circuit ground should be floating
and not be connected to the chassis ANYWHERE except a single lead from mains
ground to the star point. This will eliminate any ground loop induced hum in
your application circuit which can be a real problem to fix. To test this,
remove this mains ground lead to the star point and measure the resistance from
the chassis to the application circuit ground. It should be infinite. (If you
get a reading of less than about 1 meg ohms, then you have a stray ground
getting into your circuit that needs to be removed). Then reconnect the lead.
Rick

Tal Bejerano - AMC wrote:

> when you are talking about "ground", do you mean physically connect to mains
> ground?
>
> Regards
>
> Tal Bejerano
> AMC - ISRAEL
>
> -----Original Message-----
> From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On
> Behalf Of rixy
> Sent: Sunday, June 23, 2002 3:33 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: Hum problem
>
> Hum can be an annoyance when designing high gain audio circuits. I assume
> this
> because your previous posts discusses high quality audio circuits. There is
> nothing wrong with your power supply schematic electrically. However, all
> ground returns MUST return to only ONE point in your power supply circuit.
> Each capacitor, regulator, transformer common must go to one point in the
> supply. In your application circuit you must adhere to the same rule. All
> grounds must return to one physical point. Even a ground plane isn't
> considered good audio ground if you enter the ground plane as much as 1 inch
> apart. Consider the ground trace as a continuous resistor. Then you may see
> that a lead going to any point on the ground isn't really getting to a clean
> audio ground. In the audio world we call this point a "star ground" or "star
> point". Also, it is not the thickness of the trace that determines its
> effectiveness of a clean ground, but rather its direct and untouched contact
> with another circuit on its way to star ground. Component placement doesn't
> necessarily aggravate the hum as much as a ground loop does.
> Rick
>
> Tal Bejerano - AMC wrote:
>
> > 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
> >
> >   ------------------------------------------------------------------------
> >                   Name: psu+-12.jpg
> >    psu+-12.jpg    Type: JPEG Image (image/jpeg)
> >               Encoding: base64
>
> --
> 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
>
> --
> 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

--
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