Author Topic: Shielded wires necessary for true bypass looper?  (Read 379 times)

dave999z

Shielded wires necessary for true bypass looper?
« on: February 09, 2018, 03:15:35 PM »
Hey all -

I’m building a 14-loop true bypass looper in an aluminum enclosure.

There will be 14 3PDT footswitches, 28 associated TS send+return jacks, a pair of TS jacks for a passive (always on) loop to go to the preamp, a pair of TS jacks for input+output, and a 9v power in for the LEDs.

Due to the locations of the switches & jacks, there will be some rather longish (maybe like 12”) wire runs inside the case.

When wiring guitar harnesses, I’ve used RG174 shielded wire for the (relatively long) wire run to the output jack (and grounded the shield only at the jack end), which seems to work well at limiting hum.

I’m wondering, inside this aluminum enclosure, will that be necessary for the longer wire runs?  I wouldn’t think the antenna effect hum would happen inside a metal enclosure.  But maybe shielded cable is still needed to prevent crosstalk or oscillation?  I will try to route input/output and send/return wires away from each other, avoid long parallel runs, and try to cross wires at 90 degress, though there are limits to all that.

Coax is expensive, more work to ground the shield, and thicker so more unwieldy to route.  So I’d like to avoid it if possible.  If necessary though, I’ll use it (or a twisted grounded wire as a shield) for each long signal wire.  I want this to come out right.

Any thoughts prople have about the necessity of shielding these longer wire runs would be much appreciated.  Thanks in advance.

Dave
« Last Edit: February 09, 2018, 03:22:03 PM by dave999z »

GibsonGM

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Re: Shielded wires necessary for true bypass looper?
« Reply #1 on: February 09, 2018, 10:16:45 PM »
As long as the routing is good, I would ASSUME you are ok not shielding,  being inside the grounded enclosure.

But I am only assuming, which could make an ass out of you and me  :)   

Now, devil's advocate...couldn't you just use a lightweight, shielded wire (is the 174 light?  I've seen some pretty light stuff that still has shield, doesn't need to be coax...I'm thinking the wire good RCA cables are made of) would give you insurance (and assurance?) that you'd only do the job once...I'm assuming you'll be sending to a recording *device* and returning, etc....so levels will be changing, and be higher than what you input...insurance is nice.  I don't do shielding for basic stomp boxes, but with 'two in one' effects, or bigger preamps, I do - it seems to avoid trouble and is little bother...

Just my 2 cents.  Welcome to the forum, Dave!
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dave999z

Re: Shielded wires necessary for true bypass looper?
« Reply #2 on: February 11, 2018, 11:05:31 AM »
Thanks for your thoughts.

I donít have rca cables laying around, so rather than spend any $ on those, Iíll just use rg174.  Itís actually only like $20-25 for the amount I need from Small Bear.  Thought it would be more than that.

Iíll just solder the shield to ground at the jack end of every cable.  Will be annoying to wire up, but should prevent problems later.

GibsonGM

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Re: Shielded wires necessary for true bypass looper?
« Reply #3 on: February 11, 2018, 11:10:34 AM »
Sounds like a plan.  I haven't used 174; don't know how flexible it is.  Probably really good stuff, tho.   

A little overkill in the shielding dept. never hurt anything :)
MXR Dist +, TS9/808, Easyvibe, Big Muff Pi, Blues Breaker, Guv'nor.  MOSFace, MOS Boost,  BJT boosts - LPB-2, buffers, Phuncgnosis, FF, Orange Sunshine & others, Bazz Fuss, Tonemender, Little Gem, Orange Squeezer, Ruby Tuby, filters, octaves, trems...

amptramp

Re: Shielded wires necessary for true bypass looper?
« Reply #4 on: February 12, 2018, 06:15:19 PM »
It's quite convenient that the outer diameter of RG-174 is 0.100 inches so you can wire a row of cables to a piece of vero or a pre-patterned board.  If you have 12 inch runs like you say, I think Shielded cable would be a good idea.  You may have an application where you could get away without shielding but you can guarantee if it is shielded, it will work regardless of what you have connected to it.  The inner wire is 0.019 inches / 0.483 mm so it is easy to solder to a lot of standard board types (if you get the cable from Allied Wire and Cable - other manufacturers may have slight differences).

PRR

Re: Shielded wires necessary for true bypass looper?
« Reply #5 on: February 12, 2018, 10:47:31 PM »
14 similar clean sane signals in a box, I would not shield.

But here you could have Mega-Dupa-FUZZ!'s raucous output, while you are working a very clean sound, and the FUZZ!'s hash will leak into the clean signal.

Or not, if all input is cut from the FUZZ! and it doesn't go nuts just talking to itself.

So it is situation dependent.

Anyway: mock up TWO loops in some old box, put your nastiest distorter and your Ivory-clean buffer through, and listen hard.