A daft question from a newbie

[salviablue]

Hi guys,
I have just returned to the DIY electronics world after 15 years or so and have just dived into the deep end only knowing how to swim w/armbands (I only knew some basics back then!). Basically i have started to build lots of music orientated circuits, most quite successfully but have started to come up against some confusing schematics. I have just started on some designs for studio units and am being slightly baffled by lots of little triangles going nowhere (usually where a ground symbol goes). Now in some of these circuits i have been treating them as `to ground` since there has`nt been the trad ground symbols, but in some of these circuits there are `to ground` symbols aswell as little triangles aswell as filled in triangles (not components i.e. diodes, opamps etc)?!?
One particular circuit is this on from Silonex for an expander:
http://www.silonex.com/audiohm/expgate.html#

What is the little off board bridge thing. The one with two little triangles linked together, one called A and the other called SC?
I figure +15 and -15 are to the power supply and V+SC and V-SC are the +ve and -ve rails for the circuit and SC is maybe the ground (earthing) but what is A? It cant also be ground, can it, would that cause a ground loop (+noise)?

I have been noticing these little triangles a bit now on the more complicated circuits i have been looking to build and it would be great if they cuold be explained to me. A little `quick` info would probably give me the jump start to properly research ground and earth effects in audio again (currently i keep getting side tracked, whiling away hours `learning` about all but what i wanted!).

Cheers. (A bit of an embarrassing 1st post though!)

 

[Papabravo]

It means the two grounds are connected together at a single point. The ostensible reason is that noise on one ground has to go all the way back to the single point to affect circuits on the "other" ground.

Remember the following piece of doggerel:
Ground is Ground the world around.

 

[Roff]

SC is presumably Signal Conditioner (?) GND, while A is maybe Amplifier GND. I could only find 5 A GNDs. The intent is probably to keep the two GNDs separate (planes, preferably), and to tie them together at only one point (the little "bridge"). This could be a wire jumper, or a narrow copper strip connecting the two planes. This keeps the SC current from flowing through the A plane, potentially contaminating the audio.
You don't need an earth connection.

 

[salviablue]

special ground principle i think (buss or star point)

Thankyou all very much for the replies. I actually found an article on a ground noise reduction and avoiding noise through ground loops called something like the "Star Point Ground" principle. Your replies has confirmed alot for me and i feel quite a bit more confident in taking on these projects, cheers guys!
I thyink you are right, they are signal ground and chassis ground connected through a buss ground. I think i will star point ground them though as i have a few modules/units to build and i want them all to run of the same power supply to eliminate transformer noise.
Cheers guys

 

[philba]

I believe star point is different from the above technique. it tries to keep the grounds at as close to the same value as possible. the bridge technique is designed to segregate the noise subsystems - like analog from digital. there is a pretty good article on this topic that I found via a google search but I didn't save a link. a quick look didn't turn it up. sorry.