Building a Junction/Input box...
Jul 30, 2008 at 9:14 PM Thread Starter Post #1 of 18

guitarman19853

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Okay I've asked this on a guitar forum with no responses... So now I'm going to turn to the real audio experts. Really (I think) this is more a question of grounding and isolation.

I need to build an input/junction box for a guitar pedalboard.

Its really simple, 5 in's on one side going directly to 5 outs on the other.

I built one with radio shack parts. non-isolated jacks and a plastic enclosure. Regular hook up wire. It hummed like crazy when i hooked it up. Quick fix was to shield the box with aluminum foil but even that didnt work too well. So I bought parts to rebuild the box with good parts. Switchcraft isolated jacks (with the 3rd closed circuit pin) and an aluminum enclosure. Still same hook up wire. Much better, but still hums.

Clearly I don't know how to properly hook these up so before I go into detail of the way i have it now, how should it be wired?

Thanks! I should've come to head-fi from the beginning for this question.
 
Jul 31, 2008 at 3:15 AM Post #2 of 18

guitarman19853

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This is really a simple question:

How do you wire up a pass through box (1/4 mono in 1/4 mono out, but with 5 of them completely separate).

I just connected + to + and ground to ground as if it was just another length of cable but this isn't working. Still bad hum.
 
Jul 31, 2008 at 4:43 AM Post #4 of 18

akione

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You'll need to use screened lead for each 'pass-through'. Normal hook-up wire won't do.

Perhaps you should have tried the non-isolated sockets on the metal enclosure.
smily_headphones1.gif


You need to have the cable screens grounding to the case and all the sockets grounded on the case.
 
Jul 31, 2008 at 8:13 AM Post #6 of 18

ruZZ.il

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That really depends on the nature of all the grounds of the devices that are connected to it. Some may be floating, some may be tied somehow to the wall AC, who knows. I think it may be fine to share the ground between 2 devices, specially if one floats.. but 10 may be problematic all funky current loops and the such... I'd probably, as suggested, just use shielded cabling to shielded/isolated jacks.. Mogami/Canare cabling?
 
Jul 31, 2008 at 10:12 AM Post #7 of 18

guitarman19853

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Not all of the wires are to the same signal chain. 4 of the 5 are for my electric signal chain and the 5th one is used for 2 things depending on the way my board is configured, either acoustic signal or footswitch for electric.

My biggest problem is that I don't understand the whole ground concept. When I originally made it, i thought + to + and - to - and that should do it. I guess this isn't the case. Guess I should start looking for shielded cable...

Should i do anything with the closed circuit terminal on these jacks? They're just unconnected at the moment.
 
Jul 31, 2008 at 11:11 AM Post #8 of 18

akione

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Quote:

Originally Posted by guitarman19853 /img/forum/go_quote.gif
.....Should i do anything with the closed circuit terminal on these jacks? They're just unconnected at the moment.


I think you need to be careful here. It's tempting to think the jack should short when nothing is plugged in, but you need to
protect the other end in case whatever it's connected to doesn't like being shorted. In other words, for the moment play safe
and just wire it straight through with screened cable. You could use an old guitar lead if you have one for the internal wiring.

Alternatively, If you twist the signal and grounds together, that should also get rid of the hum, if you want to try with your existing wiring.
 
Jul 31, 2008 at 11:15 AM Post #9 of 18

akione

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Quote:

Originally Posted by guitarman19853 /img/forum/go_quote.gif
......My biggest problem is that I don't understand the whole ground concept. When I originally made it,
i thought + to + and - to - and that should do it. I guess this isn't the case. Guess I should start looking for shielded cable...



Nothing wrong with your thinking.
smily_headphones1.gif


You just need to bear in mind that unshielded wires will pick up hum. You need to counter it in some way.
Either by using screened leads or twisting the signal and grounds together to shield the signal wires.
 
Jul 31, 2008 at 1:03 PM Post #10 of 18

guitarman19853

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where can I buy shielded cable? At the most I need only about 2 ft and thats probably going to leave a bunch left over.

I thought that the ground carried signal too, which is why i thought they had to be connected. I know my amp footswitch uses both the signal and the ground wire because it manages to use a mono cable for a two button footswitch. But my most recent addition to the pedalboard required me to remove the amp footswitch for an acoustic setup.



Those interested in guitar gear, my pedalboard goes:
Electric in -> Boss GT-10 -> BBE Sonic Stomp Sonic Maximizer -> Boss Foot Volume -> Power Amp in on Fender Hot Rod Deluxe

GT-10 has a 2 button footswitch connected to act as CTRL 3 & 4. and the Hot Rod Deluxe preamp is connected in the GT-10's FX loop, also known as the 4 cable method.

The acoustic runs in to a BBE Acoustimax which is a pre-amp, sonic maximizer (can you tell I like these things?), and DI box directly to the board.

Both the electric and acoustic rig have a tuner output running to a Y cable into a Peterson Strobe Stomp II virtual strobe tuner.

Also in the pedalboard is a Sennheiser wireless unit for wireless in-ear monitors, which I use my ER-6i's (see, I related this back to headphones after all!). Theres room for a wireless guitar receiver but that can wait as I don't have a need for it at the moment.

I will take a picture of this monster tonight, and it really is a monster, with the new Acoustimax, the weight has to be in the 50-80 lb range.
 
Jul 31, 2008 at 1:37 PM Post #11 of 18

BrianDonegan

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Quote:

where can I buy shielded cable?


.

Buy/find a short RCA patch cable and cut it up. Use the center connector for the + connections and the shield for - connections. It's that simple.
 
Jul 31, 2008 at 2:12 PM Post #12 of 18

guitarman19853

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Actually if anyone is familiar with George L's cable, I have enough left over to wire this box with it. It's shielded as it's a guitar cable. That should work, right?
 
Jul 31, 2008 at 5:04 PM Post #14 of 18

guitarman19853

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Okay so I'll have shielded wire, I have shielded jacks, should I go the last step and put something to cover the solder terminals on the jack? I don't think I can get heat shrink large enough, but maybe there is something else I can use. If I'm going to shield everything else, might as well cover the last exposed point.... Electrical tape?
 

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