[sdiy] keeping signals seperate..avoiding noise

[Justin Owen]

> -----Original Message-----
> From: Laurie Biddulph [elby_designs at ozemail.com.au]
> Subject: Re: [sdiy] keeping signals seperate..avoiding noise
>
>> As a matter of good construction, the power supplies for each board should be run direct to the main power supply in
>> what is sometimes referred to as `star' fashion. 
>
> Would the same apply to pots wired as volume controls - i.e. where one pin goes to Earth/Ground?
>   
> For panel controls it may be better not to use star-earth if they are also earth-connected through a metal panel as you > could get ground loops (=hum). 

Sorry Seb (and Dan for hijacking your thread! - er, and/or anyone else...), just to clarify the whole ground, chassis earth, metal stake in the ground/earth thing!

If, for example, I had a circuit spread over three x PCBs - one is a 78XX power supply, one is - let's call it the 'motherboard' (a few op-amps) and one is just pots - let's say it's all volume controls, with one pin of each pot going to Ground - i.e. the middle pin of a 78XX VReg.

I have two separate leads, both running from VCC of the 78XX to the motherboard - one to power the op-amps and one to provide a reference voltage of VCC/2 via a voltage divider (2 x 10k resistors). There is also a lead running to the motherboard which is Ground (i.e. from the 78XX).

One pin on each of the volume pots on board 3 has to go to Ground (of the 78XX) - so should it

a) go via a separate lead from its own board to the 78XX/power supply board
b) go to same point on the motherboard where Ground from the power supply is connected, or...
c) in a small, single-supply circuit - it's not going to make much difference.

Some clues on this would take one more good solid unanswered question off my list!

Thanks

Justin