Does shielded cable make a difference in all applications?

[spargo]

I've been doing some reading on the forum lately about shielded cable, particularly from the input to the switch and from the switch to the output.  What I've come across most is doing something like this in a Dr. Boogey because of its pickyness, and it should help to keep it quieter.

Would shielded cable make much of a difference in more "normal" applications, such as with your average overdrive or distortion pedal in terms of noise?  Would it help to keep things a bit quieter at high gain settings?

Can anyone recommend some quality shielded cable?  Single conductor only is necessary.

[deadastronaut]

hi spargo,

when i build a boogie i have the shielded wire from the switch to the pcb input only...never had a problem with noise/oscillation/radio etc...

i use bits of RCA leads as shielded wire...seems ok.

i get what your saying though, it would be interesting to see if there is any difference shielding other areas/ outs/pots etc...

edit: i would shield on any overdrive/distortion/...might be good practice to just do all pedals, maybe!...

[Mike Burgundy]

Some circuits seem a bit more picky than others, but usually it's directly coupled to the amount of gain the signal sees after that wire and the input impedance of that stage. More gain means everything else that is picked up by that wire connection is also amplified. If the signal is then clipped heavily, a stray RF signal, 50Hz cycle from fluorescent lighting, or even crosstalk from other bits of the circuit can be amplified to significant level compared to maximum output - you'll start to hear noise, or experience oscillation. Higher input impedance makes it more succeptible to stuff you don't want too.
The (Aluminium) box doesn't hold back everything, not as good as ferrous metal does. Shielding the input wires helps with this. You could shield *everything* but you'll run into the rule of diminishing returns quite quickly. Usually anything after the clipping stage doesn't add to noise reduction if you use shielding - it'll help but te difference will be so minute as to be unnoticable.
It won't help with thermal noise and other things that are caused by the circuit components themselves.
Circuits with clocks in them can cause trouble too (clock getting into the signal), shielding certain bits (close to the clock, or highly amplified afterwards) combined with good box layout (experiment!) can help here too.

[Mark Hammer]

If a box is well laid-out, then shielded leads inside may not make that much of an audible difference.  The concern is for high-gain units that are not especially well laid-out, where there is a risk of oscillation by teeny signals picked up from the output and fed back through a lot of amplification.  At the very least, one should use a shielded lead from the input jack thru switch to board, such that the input path is relatively immune to picking up stray signals.

Another recommended use is in pedals that have any sort of high-frequency clock in them, such as chorus, delay, and flanger pedals.  Again, the concern is for stray signals being picked up by wires passing near them; for example wires running to a blend/mix pot passing directly over the clock-generator chip.

[deadastronaut]

At the very least, one should use a shielded lead from the input jack thru switch to board, such that the input path is relatively immune to picking up stray signals.

ok i'll do that on this pedal, im building a double dr boogie at the moment, i did wonder about the shielding considering it has 2 volumes 2 gains and 2 footswitches...

so it should be ok with the jack to switch and to pcb in, shielded then do you think?...it has fairly long wires from the pots to the 3pdt...from gain and volumes...hmmmm...

cheers mark. rob.

[R.G.]

Shielded signal wire shields against capacitive signal pickup. It helps you almost not at all for magnetic pickup. For this shielding, you pay the price of the shield-to-conductor capacitance itself. If the advantage you get from shielding (in exclusion of hum or crosstalk) is worth the loss of treble you pay by the extra capacitance, then you should use shielding.

This is quite vague, I realize, and depends very strongly on the specifics of where the wires go in that one pedal and the impedances of the source driving each wire.

There is **nothing** that is an guaranteed panacea to "add tone".