A few beginner questions regarding grounding

[SimonRichie]

Hey all,

New to this. Digging it. Have some questions that Googling hasn't answered.

1. Why would one want to isolate input and output jacks from a metal enclosure?

2. Does using metal jacks ground the guts, or do I need to run a wire to the enclosure as well?

3. I've seen a lot of gutshots where the output jack has nothing connected to the tip. What's up with that?

[IvIark]

You wouldn't want the input or output sockets isolating from the box apart from certain things like maybe a speaker output when you are told it requires isolation.  If you do isolate standard sockets from the box you will need to ground them both by wire and you'd still also want to ground the box some way.

Whereas with the open type sockets you only need to connect one because then the other is grounded through the box.

[Frank_NH]

Regarding (3), you need to make sure both of your jacks are wired with tip and sleeve connections.  Without a tip connection I'm not sure how you'd get a signal!  Here's the wiring diagram I used until I started using 3PDT boards to simplify the wiring a bit.

[Beaker]

1. Why would one want to isolate input and output jacks from a metal enclosure?

As Mark says, 99% of layouts DO NOT isolate the jacks from the enclosure. A common newbie (I've done it myself) - fault is poor mechanical (and therefore poor electrical) connection between jacks and the enclosure, due to paint / lacquer etc. around the hole. This can cause a whole load of grief. Remember all connections NEED  to be mechanically and electrically secure.


2. Does using metal jacks ground the guts, or do I need to run a wire to the enclosure as well?

To answer your second point first, there are a few builders who will screw a "Star Ground" point to the enclosure, but it's not really neccessary.

If you mean by the term "guts" - everything inside the enclosure, then if you think about it, everything in the enclosure - board, pots, jacks and switches, HAS TO BE connected to the sleeve connections of your input and output jacks (as it is the sleeve connections that carry the ground). By mounting the pots, jacks and switches into the enclosure, they are by definition, mechanically and therefore electrically connected to the aluminium enclosure. This forms a very effective Faradays cage around the "guts", helping to keep everything grounded, and to keep out stray electro-magnetic interference ( in my case usually taxi radios and German pop music stations for some strange reason).
 
Tip: After a couple of early defective builds I now ALWAYS do a continuity test between the enclosure and all switches, pots, jacks and ground, just to be sure that they really are electrically connected.


3. I've seen a lot of gutshots where the output jack has nothing connected to the tip. What's up with that?

I think you are slightly mistaken here. As already pointed out - no jack tip connection, no sound. I think what you have seen is builds with no jack RING connection, (usually on builds that do not use a battery), or no SLEEVE connection. If you have good mechanical and electrical connection between your jacks and the enclosure, you don't really need a sleeve connection, so some builders leave them out - it sure looks neater. The problem comes when the jack sockets work loose from the enclosure over time, and as a result you lose your ground connection between input and output. Not good. This is why most builders run a wire from input sleeve to output sleeve, it's just a "Belt and braces" thing.

Hope this helps.

p.s. Frank's diagram is a good one to use as a reference.