VERY NOISY "SORT-OF" A/B BOX (HOMEMADE CONTENT)

D

darnright

RepententRodentologist
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It's basically an A/B box w/o a switch. But is has a lot of hum...much worse when any distortion is added.. This is present with 2 amps connected and a guitar connected. Same brand of amps and cords are all good. I have checked continuity on all circuits and they are great. Do I need some type of noise suppressor?
Very little (normal amount of) noise when I connect a guitar with any of the three cords to either of the amps

I appreciate the help guys!!

Thanks, Dave
 
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Re: VERY NOISY "SORT-OF" A/B BOX (HOMEMADE CONTENT)

2 things... First... Very cool you were able to make one!!!!
second.. Im not ANY kind of wiring guru, so not sure I can help. But, looking at the wiring, Im wondering if you need some kind of ground??
 
Re: VERY NOISY "SORT-OF" A/B BOX (HOMEMADE CONTENT)

BloodRose said:
2 things... First... Very cool you were able to make one!!!!
second.. Im not ANY kind of wiring guru, so not sure I can help. But, looking at the wiring, Im wondering if you need some kind of ground??
Click to expand...

My thought exactly. I’m also far from a wiring expert but a metal fx box where a ground connection could be made seems like a possible solution.
Plus those boxes are fairly cheap.
 
Re: VERY NOISY "SORT-OF" A/B BOX (HOMEMADE CONTENT)

Gtrjunior said:
My thought exactly. I’m also far from a wiring expert but a metal fx box where a ground connection could be made seems like a possible solution.
Plus those boxes are fairly cheap.
Click to expand...

Yep.

I'm sure metal box would fix the issue: It's basically antenna without it. You want grounded metal box around it for shielding.
 
Re: VERY NOISY "SORT-OF" A/B BOX (HOMEMADE CONTENT)

Isn't it grounded already with the cables? It's literally like a y cable.

Even if it gets "grounded" what he described are the typical issues of any passive a/b box. Not sure they will be gone.
 
Re: VERY NOISY "SORT-OF" A/B BOX (HOMEMADE CONTENT)

Would a switch that disconnects one of the grounds after the split work out as a ground lift?

Sent from my SM-G930U using Tapatalk
 
Re: VERY NOISY "SORT-OF" A/B BOX (HOMEMADE CONTENT)

Yes, the grounds are connected (the ring connection on the jacks), but the wires are no longer shielded. If you put it in a metal box the grounds on the jacks will connect to the box when you install them, no need to run a separate ground wire, and it will shield the wires. It's also assuming that you connected all the rings together and all the tips together, you didn't "cross the streams" (it looks correct).

FuseG4 said:
Would a switch that disconnects one of the grounds after the split work out as a ground lift?
Click to expand...

The shield/ground in a guitar cable is the return path for the signal, if you lift it, there is not signal. It's not like a low impedance signal with 3 conductors.
 
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Re: VERY NOISY "SORT-OF" A/B BOX (HOMEMADE CONTENT)

darnright said:
View attachment 96407

It's basically an A/B box w/o a switch. But is has a lot of hum...much worse when any distortion is added.. This is present with 2 amps connected and a guitar connected. Same brand of amps and cords are all good. I have checked continuity on all circuits and they are great. Do I need some type of noise suppressor?
Very little (normal amount of) noise when I connect a guitar with any of the three cords to either of the amps

I appreciate the help guys!!

Thanks, Dave
Click to expand...
Maybe rewire it with shielded cable.
WB1508-single-core-ofc-screened-audio-cable-sold-per-metreImageMain-515.jpg
 
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Re: VERY NOISY "SORT-OF" A/B BOX (HOMEMADE CONTENT)

The shielding issue aside, any kind of passive Y connector like this would connect the signal input hots together and the signal input grounds together, and I reckon some amplifiers don’t take kindly to that sort of thing. A good active box should solve the problems you’re encountering. I don’t know enough to design one, but I know enough to trust Radial to build one.
 
Re: VERY NOISY "SORT-OF" A/B BOX (HOMEMADE CONTENT)

devastone said:
The shield/ground in a guitar cable is the return path for the signal, if you lift it, there is not signal. It's not like a low impedance signal with 3 conductors.
Click to expand...

Actually, if both amps are grounded through their power cords, then breaking one of the "sleeve" (gray) connections in this box with mini-toggle switch will kill the ground loop hum. The signal path will be completed by the amp chassis and ground wires. It's not the best way to kill a ground loop but it will work, better if the power cords are short and plugged into the same outlet.

The lack of shielding by the plastic box is another concern. Problem is, if the OP switches to a metal box, the jacks he used provide no way to isolate the sleeve from the metal box. Then there's no way to kill the ground loop.

I needed a similar Y-connector box to split my guitar out to my pedalboard on one side, and a small amp powering a talkbox on the other. I didn't want to invest in a transformer-isolated A/B/Y box (like a Radial) just for one gig, so I built this:

Y-Box.jpg

The metal jacks on both ends are solidly grounded to the box, which shields the connecting wires inside. The plastic jack on the side has its sleeve connected to the box through the switch, so it can be grounded or not. Guitar goes in one end, main amp comes out the other end, and the second amp connects on the side. Then I just select whichever switch position is quieter.
 
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Re: VERY NOISY "SORT-OF" A/B BOX (HOMEMADE CONTENT)

I'm going to guess the quieter setting for the switch is to ground the ring to the box about 90% of the time, otherwise your return path for the signal is to go through the building wiring. If the ground is lifted on the 2nd amp, you won't have any signal at all, or it will be very low, it could theoretically still come through the neutral wire after making a trip out to the fuse box.
 
Re: VERY NOISY "SORT-OF" A/B BOX (HOMEMADE CONTENT)

The signal only has to go as far as the outlet, where the two amps' ground pins are tied together. In my setup, if I used my Champ head (typical tube amp with grounded 3-conductor power cord) I got bad ground loop hum with the switch closed. Opening the switch to lift the ground off the Champ's input killed the loop and gave me a signal that was not noticeably weak. There's certainly no signal loss that can't be compensated for with a slight increase in either the volume or tone controls.

My Vox MV50, on the other hand, uses a PC-style power supply with no ground conduction between the power supply and the amp head. When I use the MV50 to power my talkbox, I have to close the mini-toggle to provided a return path through the plastic jack's shield.

Here's the whole rig, which I used for my 40th high school reunion. The wah pedal and talkbox are not part of my usual "thang", but we were playing '70s rock and were deemed necessary for the show.

G8TDXQA.jpg
 
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