Grounding input & output XLRs on SSL - a little question

Since the PCB only got one ground connection each for the input and output XLRs, are you guys just linking the two pin 1's of the input XLR pair and then just connect one of the pin 1 to the PCB?

Sometimes a pic says 1,000 words.



Jump both output pin 1s and take to PCB pad marked 0.

Jump both input pin 1s and take to PCB pad marked 0. Also input pin 1 (which are jumped together) to star ground.

PS - This was my first DIY... in 06/2004 :shock: . Doesn't really seem that long ago.

thanks alot

time flies

Ok. Seems like a good idea, simple too.

Is the PCB also connected to ground thru the PCB mount screws?

Because my REV#7 PCB has grounding connections to the chassi
when I use metal PCB mounting screws

[quote author="[email protected]"]Is the PCB also connected to ground thru the PCB mount screws?

Because my REV#7 PCB has grounding connections to the chassi
when I use metal PCB mounting screws[/quote]

Three of the four screws are grounded.

I just don't get one thing: Why not also connect the two Output Pin 1s also to chassis/earth (i.e. signal) ground?
Wouldn't this be necessary to guarantee a hum-free working environment for the device used AFTER the GSSL (or whatever)?

Because connecting the two Input Pin 1s to chassis/earth ground makes your device only hum-free because the output stage and shielding of the device used BEFORE your device are connected to the same ground. Or what did I get wrong?

Why not also connect the two Output Pin 1s also to chassis/earth (i.e. signal) ground?

Click to expand...

Just ground the input, because the pin1 of the input is the 0V of the PCB like the 0V of the Output

Yes, I thought the same way but in another thread here I read something like "it's the worst thing you can do wiring Pin 1s of Output and Pin 1s of Input together" - but in fact that's what happens, isn't it?

Another strange thing I came across: When I power plug the GSSL into a different power socket as where my amp is plugged in, I get a quite loud hum _even though_ all channels on the mixer are faded to zero (i.e. no signal is sent in any way). As soon as I wire Pin 1s of the Input to chassis/earth ground this gets even worse.
But as soon as I lift of the earth ground from the chassis it's quiet. Is that what you call "ground lift"?

As soon as I plug it into the same power outlet as my amp its dead silent.

I guess that's "normal" isn't it?

you must ground the input Pin 1 and the earth ground at the same point.
it's a 'star grounding', all grounds goes to the same point.(Audio, PSU & earth)

If your not connect the earth you got humm.@ 50/60hz

As A general rule for these analog only projects:
Have only ONE chassis ground point, with a good size, short wire from the power plug ground terminal to a star washered ground lug secured to the chassis (rack box)
From the chassis ground point, run ONE ground wire to the (or each) circuit board (including the power supply board, if there is one)
DO NOT connect any audio I/O cable ground wires to the circuit boards, connect only at the I/O connector, and run a wire from this to the chassis ground point.
If you want to be super flexible, take the audio connector grounds to ground lift switches on their way to the chassis ground.
Think about it....if there are noise currents on the audio ground cables that you are plugging in to your box, do you want them to flow through the entire audio circuit on their way to ground?
Mount the circuit boards with iso washers or plastic stand offs to be sure they do not short to ground.
This is a star ground, and elimanates ground loops
It will work very well on your GSSL
(yes, this has been stated here many times, but I hope it helps & bears repeating)

So, I'm sorry to ask again, but I just can't get rid of the hum in my SSL:
Are you suggesting to disconnect the two/four (I/O) cable ground wires from the SSL Board and plug them directly into a star ground, that means leaving out the two middle connectors in the 5-way I/O connector on the board?

I have wired my power ground to chassis and from there to the ground pin 1 of the input but I hear a quite loud hum in my SSL. When I switch it from bypass to on, it gets even louder... Can this also have something to do with me taking the power for the VU-Meter from the legs of the 7815 maybe?


The green/yellow one is ground...

Hi All,
I would suggest everybody to read - and try to put in practice - these two articles :

Designing for Interference-free Audio System Components @  http://www.compliance-club.com/archive/old_archive/020918.htm
and
Sound System Interconnection @ http://www.rane.com/note110.html

Best,
Guy

So, I'm sorry to ask again, but I just can't get rid of the hum in my SSL

Click to expand...

First of all, may I say some very nice neat GSSL construction shown here.

I found that it was impossible to get a completely hum free performance with the standard GSSL board.
This is mainly due to the fact that there are about 4 earth loops on the PCB.
I cut several tracks and re-routed some traces to get a 15dB improvement on the hum performance.
I endorce what has been said about isolating the PCB standoffs from 0v. on the board.

My preferred way is to connect the mains earth to chassis but not 0v.
Connect the XLR's to 0v. only at the PCB.
And to connect 0v. to mains earth through a 47 ohm resistor in parallel with a 0.1uF cap at the star point.
Works for me.

So are you grounding audio to chassis at one place only?
Remove this connection and use a multimeter to check to see if ground is getting to the chassis somewhere else.

I see you are joining all XLRs together. Are you then taking ground to the PCB in one place only?

How loud hum are we talking?

That picture confuses newbie  : me, the casing of the XLR's are already grounded to the bare metal of the case (from when you cut out the holes) so why ground one XLR to the case again? Is that creating another ground loop?

Also how is the PCB 0V grounded? Can't see chassis ground in that picture so where is IEC mains earth grounded to the case?