Grounding, grounding, grounding........ and... oh yeah, grounding

I may have a knack for stating the obvious, but good grounding is critical for optimum noise performance (never mind any safety issues caused by bad grounding).

A few days ago I finished (I had thought) two sets of S800 dual-channel eq's using Purusha's cases.  I connected the audio and psu grounds at the AC inlet, but neglected to connect to any part of the chassis.  So they worked fine, but I was getting some hum while mixing yesterday, and I'd get an occasional 'snap' in the signal when I'd touch the front panels.  Then it hit me that there was no chassis ground connection!

I'm a religious grounder (just ask my kids  ), but for whatever reason I totally neglected this part of the build this time around.  So last night I took them apart, used a dremel with sanding wheel to grind away some of the powder coat around enough holes in the panels to allow them to all conduct together when the chassis were reassembled, put them back together and ran a ground wire from the AC inlet ground pin to a single spot on the chassis. 

I resumed mixing with them today, and nothing but sweet silence (and nice eq with signal applied, of course).

Like I say, grounding is pretty obvious stuff, but I just missed it on this project for whatever reason, and thought it might be useful to send out a little reminder.

As you were.

JC

Perhaps you wouldn't mind fielding a grounding question?
I'm having a lot of trouble bench testing a pair of v676's...
I don't think the dc power jack has a ground lug, so I just have the shields of the i/o tied to the ground pin on the unit.  Things don't seem right, no signal just buzz, buzz changes if I touch the units.  How should I be doing this?

substitute said:

I don't think the dc power jack has a ground lug

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The dc power jack go to ground thru the case, check how is wired the Baby Animal at www.jlmaudio.com
Hope this help

How'd you know it was a JLM ps?
So as far as bench testing goes should I maybe mount the DC jack to a piece of aluminum or something and star ground the xlr's together?

hope I'm not high jacking your thread JC

V676... is that solid state class-A?  What kind of power does it use (+X dc only?)

Some of the class-A, single rail designs can be picky about grounding (i.e. Neve).

And are you, in fact, using a JLM AD/DC power supply?

JC

substitute said:

Perhaps you wouldn't mind fielding a grounding question?
I'm having a lot of trouble bench testing a pair of v676's...
I don't think the dc power jack has a ground lug, so I just have the shields of the i/o tied to the ground pin on the unit.  Things don't seem right, no signal just buzz, buzz changes if I touch the units.  How should I be doing this?

Click to expand...

If you are bench testing them make sure that you ground them to mains earth.  If you don't have this connection then the sheilding in the mic cable & the in the mic won't work properly & you can expect some buzz/hum.  I have a pair of these & they are very quiet.      It was 5 or so years ago that I racked them, so I can't remember exactly how I did it, but I know I just followed the data sheet, so chassis & audio earths are connected together on the socket without the 100R lift resistor.