Shielding enclosures and noise - best practices

[soggybag]

What's the best practice for shielding an enclosure? Should the enclosure be grounded, is it okay to not ground the enclosure?

I usually build with switchcraft jacks. These make contact to the enclosure at the ring. If you're also grounding the jack to your board it seems there is the possibility for a ground loop since the enclosure is now connected to ground at two points.

Recently I used some of those plastic Marshall style jacks and realized the enclosure would not be grounded at all.

If the enclosure is not grounded does that make a shield or does it turn the box into an antenna?

I'm not having any noise troubles with this recent build but was wonder what would be best practice. I could leave the box not connected to ground or I could run a wire from ground to one of the pots or switch?

[antonis]

Ground enclosure as close as posible to Power supply ground..

[iainpunk]

i generally use a plastic washer/shrink tube to isolate the output jack from the enclosure. the input jack is where i generally connect the battery/power jack [star ground].

If the enclosure is not grounded does that make a shield or does it turn the box into an antenna?

i believe a metal enclosure that is not grounded has a neutral effect on noise floor, but grounding it is generally good practice.

cheers, Iain

[PRR]

For "small" audio: It is better to connect box to signal common.

Boxes not much bigger than your hand and no external AC coming into the box, it may not matter "where" connection is made on box or common.

Yes, the plastic jax are a mixed blessing. On a large amplifier it avoids having multiple "chassis grounds" to manage. On a small box you may have to resort to a toothed washer to get a bond to box.

[MikeA]

i believe a metal enclosure that is not grounded has a neutral effect on noise floor, but grounding it is generally good practice.

A hopefully relevant anecdote: I got a Midnight Amplification Holy Mountain in for repair, if you're not familiar it's essentially a Green Citrus/Matamp GT120.  Had a really bad buzz.  In and out jacks were plastic/insulated, and there was no connection from signal common to the aluminum enclosure.  I ran a lead from power ground to the enclosure, which completely cleared the noise.

Another anecdote:  I have noticed when buying Hammond aluminum enclosures that are factory powder coated, that they have removed the powder coat from the countersink area of one of the holes in the back plate, so that one mounting screw connects the back plate electrically to the main enclosure.  It's not a Faraday cage by any means, too many holes and gaps, but I've still started ensuring that my enclosure backs make good electrical contact with the fronts.   

[EBK]

I always get a little preachy when talking about grounding and shielding.  This is probably because I remain convinced that grounding is part science, part religion (I've said this before).  While I won't try to convert you to my isolate-the-input-jack faith (very similar to Iain's isolate-the-output-jack approach mentioned above), I will say this:  Ground* your enclosures, and they will act as a shield. Don't, however, rely on your enclosure as a ground current conductor.  If someone tells you that you don't have to connect one of your jack sleeve terminals to anything when you are using a metal enclosure, please ignore them.  When that jack works its way loose during a gig, your audience will notice.

*I use the word "ground" very loosely, of course. There are some (of more orthodox faith) who say that you shouldn't use that word unless you are committed to driving a large metal rod into the earth.

[iainpunk]

i believe a metal enclosure that is not grounded has a neutral effect on noise floor, but grounding it is generally good practice.

A hopefully relevant anecdote: I got a Midnight Amplification Holy Mountain in for repair, if you're not familiar it's essentially a Green Citrus/Matamp GT120.  Had a really bad buzz.  In and out jacks were plastic/insulated, and there was no connection from signal common to the aluminum enclosure.  I ran a lead from power ground to the enclosure, which completely cleared the noise.

yes, of course, grounding eliminates noise but what i meant with my statement is that not grounding the enclosure is almost exactly as noisy as a plastic or no enclosure, it doesn't add noise like an antenna, like OP asks.

cheers, Iain

[duck_arse]

I usually build with switchcraft jacks. These make contact to the enclosure at the ring.

really at the ring, or do you mean the sleeve?

[soggybag]

I usually build with switchcraft jacks. These make contact to the enclosure at the ring.

really at the ring, or do you mean the sleeve?

Correct I meant the sleeve not the ring.