Using wire vs. sheilded cable

[MikeH]

I recently read something about building pedals, and it mentioned using shielded cable in certain parts of the wiring.  Does anyone know when you're supposed to use shielded cable instead of wire, and what difference it makes?

I'm assuming it decreases noise, but is it always necessary?  I used normal wire in all the builds I've done so far, and they're not excessively noisy, but could they end up producing unwanted noise in environments outside of my house?

[billings]

I would definitely want to use shielded wire for input and output in a high gain non-inverting distortion like the fuzz face to prevent the circuit from oscillating.

[John Lyons]

Usually I always do the input and output. I have pedals without either and they are fine.
With High Gain pedals it matters more. The input is the most important...

John

[bancika]

I use shielded wire all time for input/output leads and sometimes for few other leads...

[343 Salty Beans]

i often just use naked copper coil 

But then again, a few of my pedals were quite noisy and I had to do a few things to get them to shut up.

[formerMember1]

ive built quite a few fuzzfaces and never used shielded wire and have all the wires from the board together with a cable tie around them, and no problems. Never get osicallation with it, ever.  Even if I try.

[343 Salty Beans]

also, if you don't feel like using shielded wire, a ferrite on the V+ wire can tame noise. I found a load of them in a broken XBox, but I'm sure they're cheap.

[brett]

Hi
I use the "spaghetti don't oscillate" theory. 
Messy layouts have their advantages.
cheers

[Paul Perry (Frostwave)]

The input is the crucial one, if you are sheilding any.
But, to get it in proportion... the traces on the PCB aren't shielded, are they?
As for spaghetti, one day you will run out of luck. Remember, a circuit may not be oscillating, but it may be ALMOST oscillating, and a flattish battery push it over the edge. Plus, of course, an circuit that is ALMOST oscillating will sound differnt from one that doesn't have a mystery feedback path!
There is always the tale about the military gear that HAD to have the wires bound together, but always oscillated when it did..... but that's the example that proves the rule. Even there, judicious shielding would have fixed it.
In my own stuff, there is only one place in one box that I have shileded wire (low signal, high impedance points). But I don't have spaghetti anywhere either!

[lowstar]

one thing that hasn´t ben covered in this thread yet...modulation effects !
using shielded wire for the rate pot, in many cases, cures ticking. i also used shielded wire successfully for leds that blink in unison with the rate of a phaser, and it stopped ticking, too. basically, any fx that has a strong lfo somewhere in there can require one or more shielded connexions.

cheers,
lowstar

[MikeH]

also, if you don't feel like using shielded wire, a ferrite on the V+ wire can tame noise. I found a load of them in a broken XBox, but I'm sure they're cheap.

Hmmm... My diy vocab isn't up to snuff.  What do you mean by a Ferrite?  Magnetic?

[343 Salty Beans]

in a sense. It goes around the wire and in some magnetic sense or the other keeps the stray signals from getting all over the place.

Here's a thread on them:

http://www.diystompboxes.com/smfforum/index.php?topic=46614.0

[Gladmarr]

Here's what I've always wondered about in these threads about shielded/non-shielded wiring; what kind of shielded cable are people using?  I can't seem to find any coax or biax that would fit the bill.  Any suggestions?

thx

[petemoore]

  I betcha Small Bear has shielded wires.
  Tape Decks sometimes have nice lengths of shielded wire, one end nicely prepared for Gnd and center wire connection with heat shrink, the other end is easy enough to get a clean center wire out of.

[343 Salty Beans]

I know ratshack sells shielded wire, but like I said above, never needed to resort to it. I'm in the (long) process of finishing up a trem lune, may need to use shielded wire for the speed pots...but I hope not. I don't feel like buying it 

[Mark Hammer]

The cables used to connect CD/DVD drives to sound cards are generally 2 conductors (for left/right) and a shield.  They can work very nicely for folks wishing to provide shielding to pot leads, and have the added virtue of being able to plug into a header if you can stick one on your board.  They can often be gotten cheap, and turn corners VERY nicely.  One of those cables should be able to do you for 4 or 5 pots easily.

[idlechatterbox]

I realize that this thread has to do with shielding in stompboxes, so if I'm hijacking it, just tell me and I'll start a new thread in the Lounge, since my queston is about shielding in a tube amp, not a pedal.

That said, here's my questions. I've finished a project amp.

A jpg if anyone's interested:

http://s96.photobucket.com/albums/l164/idle_chatterbox/

The amp sounds glorious when it's stretched out on the workbench (aka kitchen table) and jumper wires are connecting the input jack, etc. As soon as I snug everything up and put the front cover on, it develops a hum. Did some trouble shooting and found out that the hum is due to the location/arrangment of the wires leading to the input jack. The wires aren't shielded, and with the amp chassis separated from the front panel (where the jack is mounted), I can vary the hum just by changing the bends in the jack wires, pushing them an inch to the left/right, and so on. If the wires are straight and pointed towards Mecca, there's no hum, but it's hard to keep them that way once I put everything back into place. So, in short, I've clearly got a shielding problem, as well as possibly a routing problem.

That said,
1. I have a bunch of unused rca cords, mostly from VCRs, etc. If I recall, the cables use a center wire, insulation, then a stranded wire for the ground wire. Would they work as "shielded" cable if I only ran signal through the center wire?

2. is there a way to deal with the source of the interference, rather than wait till it gets to the wire?

3. is it necessary to shield somehow the lugs on the input jack, or is that just overkill?

thanks for any suggestions 

[bancika]

1) yeah
2) well yes, but you should use shielded wire somewhere. Heater wires can induce hum so it's best to move them far from signal wires. Also, all other AC wires (from/to transformer) should be away from signal wires. Transformers also can induce hum. Signal leads should not go close to each other...
3) just an overkill, IMHO