Author Topic: Shielded wire question  (Read 13117 times)

lincolnic

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Shielded wire question
« on: September 01, 2011, 04:34:06 PM »
Hey guys,

I'm probably going to wire up my Poindexter build in the next day or two, and I'm a little unsure of where exactly I should be using shielded wire. Should it go between my in/out jacks and the switch, or between the switch and PCB? Every explanation I can find about how to use shielded wire makes me think it should be between the jacks and the switch, but I figured I should double check and ask before I start soldering.

One more question: if I shield the input and output, would it be okay to solder each wire's shield to its respective jack (i.e. input to the input sleeve, output to output sleeve) or should I have the shields wired to the same ground?

Thanks in advance.

druz15

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Re: Shielded wire question
« Reply #1 on: September 02, 2011, 06:48:04 AM »
I also would like to know I always found shielded wire confusing like when I had to use it in my plexi amp build that was the only thing i got my tech to do cause I couldn't find a single simple explanation of what to do with it in the amp

mgwhit

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Re: Shielded wire question
« Reply #2 on: September 02, 2011, 09:25:51 AM »
Shielded wire just surrounds your signal wire with a conductive layer that picks up electromagnetic interference and sends it to ground.  The best place to put shielded wire is on your input connections, as this signal will go through the most amplification within your circuit and any noise here will be amplified most. 

You must ground the shielding, and you must only do this at one end of each length of wire.  If I were going to use shielded wire I would run one length from the input jack to the footswitch, grounded at the jack, and another length from the footswitch to the board, grounded at the footswitch.

lincolnic

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Re: Shielded wire question
« Reply #3 on: September 02, 2011, 09:45:45 AM »
Shielded wire just surrounds your signal wire with a conductive layer that picks up electromagnetic interference and sends it to ground.  The best place to put shielded wire is on your input connections, as this signal will go through the most amplification within your circuit and any noise here will be amplified most. 

You must ground the shielding, and you must only do this at one end of each length of wire.  If I were going to use shielded wire I would run one length from the input jack to the footswitch, grounded at the jack, and another length from the footswitch to the board, grounded at the footswitch.

Thanks, this is exactly the info I was looking for.

druz15

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Re: Shielded wire question
« Reply #4 on: September 07, 2011, 02:31:41 AM »
so you can use guitar cable for shielded wire right? and just ground at one end?

raulduke

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Re: Shielded wire question
« Reply #5 on: September 07, 2011, 03:22:26 AM »
Guitar cable will work fine if you have the space in the enclosure and some to hand.

As someone mentioned earlier; just make sure you ground only one end of the shield.

A neat way to do it is to take the shield/braid wire that you want to connect to ground. Twist this end neatly with some standard single core wire and joint together.

You can then cover the jointed wires together with heatshrink to make a neat finish.

Hope this makes sense?

bigmufffuzzwizz

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Re: Shielded wire question
« Reply #6 on: September 07, 2011, 02:18:09 PM »
Thanks for a great explanation. I haven't encountered the need to use any yet but I'm sure I will one day.
Owner and operator of Magic Pedals

lincolnic

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Re: Shielded wire question
« Reply #7 on: September 07, 2011, 10:38:26 PM »
Having successfully used the shielded wire, let me tell you guys - I hope I don't have to use it again any time soon. I kept accidentally pulling the signal wire out of the entire package while trying to strip it, which became more of a pain when I'd accidentally pull the shielding along with it. Ah well...hopefully next time will be easier, whenever that ends up happening.

mgwhit

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Re: Shielded wire question
« Reply #8 on: September 08, 2011, 05:48:35 AM »
I built a Chunk Chunk (using lower gain 2n5457's) last week and didn't bother with shielded wire, even though the jack-to-switch runs are a few inches long (top-mounted jacks on a 1590BB).  There's some hiss when you crank the gain, which I assume is from the board components, but no hum at all.

I'll play with J201's later this week and see if any hum materializes, but if a Chunk Chunk doesn't need shielded wire I can't imagine where you would really need it.  Maybe I'm wrong, and shielded wire would fix the hiss.  Or maybe my lead dress is just too awesome....  ::)

raulduke

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Re: Shielded wire question
« Reply #9 on: September 08, 2011, 06:15:45 AM »
Shielded wire will reduce hiss and hum.

However, I think with leads at a few inches long it won't really make any difference (or a minimal difference anyway) as you say.

D*A*M pedals for example only seem to use shielded cable on runs that look around 4 inches or over from what I have seen in photos.

And those pedals are built like tanks.

I think using shielded wire is a bit like shielding guitars; in some environments it will make a noticeable difference and in others the effects will be negligible.

Rockhorst

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Re: Shielded wire question
« Reply #10 on: September 08, 2011, 07:10:19 AM »
I built a Grapevine with jacks on top, normal wire: dead quiet. I shielded my MIM Strat: same noise as any given factory Strat...I stopped bothering.

sgmezei

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Re: Shielded wire question
« Reply #11 on: September 08, 2011, 09:40:23 AM »
I am glad to read everyones thoughts on this. I have seen a ton of builds with shielded wire going from the input to footswitch and from the footswitch to the output. This never really made sense why these two places. I understand the input, but wouldn't the signal be shielded by the metal enclosure?

I have used it in some builds but it is hard to AB the two types of wiring. I hope people keep posting their results/experiences.

mgwhit

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Re: Shielded wire question
« Reply #12 on: September 08, 2011, 12:13:23 PM »
A properly grounded aluminum enclosure should take care of most electromagnetic interference coming from outside the pedal, and -- unlike a guitar amplifier -- there shouldn't be any significant power supply AC inside the enclosure.  That being said, almost all builds have large electrolytic caps on the 9VDC input anticipating residual ripple from cheap power supplies, and the circuit board and wiring certainly have the potential to introduce noise through improper layout.

I think the rationale behind shielding the input and output wires is that they are potentially the longest off-board signal paths in the pedal.  The input is of primary concern because any noise on that wire will receive the full amplification of the pedal.  And remember, even if your pedal isn't a volume monster or you're running it at unity gain, almost all pedals have to amplify at some point to make up for gain loss elsewhere in the circuit.  The output wire might be of less concern, but its signal will be amplified again by at least your amp and possibly other pedals in your chain.

If your input/output wires are short and nowhere near the board, shielding them is probably a waste of time, but I can understand the concern if they run the full length of the pedal and/or run parallel to other parts of the circuit (*cough* like mine *cough*).  I'll poke around the input/output wires on my Chunk Chunk and see if it affects the hiss at all.  I assumed (perhaps incorrectly) that the hiss was just the product of four noisy transistor gain stages.  If it does seem to be being picked up by the wires, I'll certainly experiment with shielding them.
« Last Edit: September 08, 2011, 12:15:25 PM by mgwhit »