Hello, I'm almost done with my QTB shielding job and I'm wiring the output jack.
I don't have the 3 conductor shielded cable (2 inner conductors, 1 shield) that is recommended for this mod, but I have some 2 conductor shielded cable (1 inner conductor, 1 shield) from an amplifier build I completed recently.
I will admit to being a newbie on electronic theory and application, but I'm thinking of using the shielded cable I have with the inner conductor going from volume pot hot wiper to output jack hot. The shielding on this cable would be unattached at the volume pot (shrinkwrapped), but would be soldered to the output jack ground tab.
Separately I am planning on running a plain wire from volume pot ground tab to the output jack ground tab.
Does anybody see any ground loop or other problems in wiring the output jack in this way? An alternative would be to use another length of the 2 conductor shielded cable for the volume pot ground tab run to output jack, but I'm wondering how necessary it is to have a shielded run on that ground wire.
..... but I'm wondering how necessary it is to have a shielded run on that ground wire.
Hi David, and welcome!
I am an electronics newbie too, so I can't answer this - I think I'll leave it to the guys who really understand it - BUT ...
I did this mod last summer, and I found that - in my honest opinion - shielded wire was a big pain. I used plain old wire with a plastic casing for everything, and I do not believe anything suffered for it.
The cavities were well shielded, and the plain old wires to the capacitor provided the shock protection.
Again, I would wait for the input of others before you rely on my thoughts here, but I do wonder - on the same topic as part of your question asks - if it is necessary to have a shielded run at all.
If it isn't, then avoiding it may eliminate your ground loop concerns altogether? (I am totally guessing on that )
In the meantime, hang tight. Experienced opinions are on the way
You don't need to shield a ground wire, that's for certain. But you do need to have two wires running out to the output jack, so here's what I'd do:
Shield the jack's cavity (if it's separate), and let the jack mounting plate rest on that shielding foil (hidden from public view, of course). Run a twisted pair of wires from the volume pot's wiper and the ground lug/ring to the jack, and solder appropriately. Twist the pair such that one complete rotation occurs every inch or so - not too tightly, and not too loosely. Consistency is the name of the game here.
In effect, I'm suggesting that you not rely on the shielding foil/paint itself to carry the ground part of the signal over from the main cavity to the jack cavity, and thus to the jack - that's asking for potential problems, IMHO.
I don't think it's worth the effort and expense to use shielded wire for anything less than 6" of otherwise unshielded length. (Inside a shielded cavity doesn't count towards that six inches, I'm talking about the space between shielded cavities.)
You seem to be on the right track as far as avoiding ground loops is concerned, keep at it, and all should be well when you've finished your project. Good luck!
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