New Ground Loop..Effect Gizmo, Pedalboard and Amp head. Help needed

luca9583

Well-Known Member
Hi Ron

I'm experiencing a new ground loop in my setup.

Pedalboard (GT 16, Switchblade 8F, bunch of pedals, Kenton Midi Thru, Pedal Power 4x4)
Effect Gizmo (1-4 in front of amp, 5-8 in amp's loop) on a rack.
Mini Line Mixer
Marshall 410H

So when i run the pedalboard direct into the amp without the Gizmo connected to anything there is no hum.

When i hook up the Gizmo to the Marshall for both pre and post effects there is no hum.

As soon as i put the pedalboard into the Gizmo's front input i get hum.

The Gizmo is in a rack that has 3 other pieces of gear (Drawmer DS201, ISP Pro Rack G, Digitech Quad) that are currently not connected to the Gizmo and powered down for troubleshooting purposes...all rack units including the Gizmo are mounted with humfrees.

If i run the Gizmo only into the front of the Marshall (without the amp's loop for post fx) and the pedalboard into Gizmo front input..i still get the hum.

I also noticed something strange...the hum is slightly reduced (tiny amount) if i power the GT 16 from the Pedal Power 4x4 (surprised this was enough to power the GT) instead of it's own laptop style power supply, and also if i remove the Kenton Midi box's power..but the hum is still there.

Everything is powered from the same outlet.

Is it possible that the Effect Gizmo doesn't like the signal coming out of the Switchblade 8F?
 
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I would look at the MIDI connections first - I have to wonder if there's a ground in there that shouldn't be there.

Try these tests:

- Disconnect the MIDI cable from the pedalboard to the rack
- Reconnect the above, then disconnect the MIDI cable from the Switchblade
- Reconnect the above, then disconnect the MIDI connection from GT to Kenton
- Leave the GT to Kenton connection disconnected, connect GT directly to Rack

Do any of those things get rid of the hum?

Also, try using an isolation transformer on the audio connection from the pedalboard to rack. It's not the best long term solution, but is also a good test to pinpoint the location of the ground loop.
 
Thanks a lot Ron. All my tests so fare were done without midi connections.

Isolation transformer between board and rack didn't work either
 
What does the pedalboard sound like when it's plugged directly into the amp's input?
 
No for the first test that gave hum it was just board into rack into front of amp. I'm wondering if, despite the humfrees, that something in the rack itself is causing the hum (the rack case itself or something insides one of the other rack units)

I guess i would need to run the Effect Gizmo outside of the rack as a further test.
 
Removed rack Gizmo from rack.
Board into Gizmo into amp still gets hum.

I also noticed that with no power going to the Gizmo, if i put an isolation transformer between board and Gizmo then the hum goes away. If i then power up the Gizmo and keep the iso transformer in line, i get a very loud buzz
 
Are you using the buffer in the Effect Gizmo? If not, try using it. Also, check the ground lift switch, try it in both positions.
 
Yep Buffer is in line as i'm going into Effect Gizmo's front input normalled to Inputs 1-4.

Tried ground lift switch and it doesn't change anything.

It seems that removing the power supplies from the GT and Kenton on the board improves the noise (these power supplies aren't a problem when board goes direct to amp). Powering the Kenton from the PP 4x4 removes any noise created by the Kenton.

At this point i'm thinking i would need to power all units on the board from a single box.

Would the Cioks Ciokolate be able to power the GT using a y cable from the 400 and 800ma DC outputs?
 
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As long as the Cioks supply allows connecting outputs together in parallel, then yes, 1200mA will be enough for a GT/16
 
Yes, it needs 1000, so the 800 or 400mA outputs will not be enough by themselves. The 1200mA combined output will be more than enough.
 
Good news in ground loop land...i moved all the pedals and Switchblade to the rack. Now the whole rack including the Effect Gizmo is powered by an N-Audio Power Box Pro and i've pretty much got rid of the hum that was happening when the Swithblade was going into the Effect Gizmo (with both units originally powered by their respective wall wart and a Pedal Power 4x4 ). The Power Box Pro also got rid of the noise caused by the Kenton's original power supply :)

Ron! I now have another question! All of the original ground loops i got rid of in this 4CM system occur between all connections between the Axe II and the Effect Gizmo & Mini Line Mixer. I used several Behringer isolation boxes to get rid of the ground loops. I have the Gizmo set up so that 1-4 are pre fx, and 5-8 are dry send and post fx send..

My question is...instead of using the isolation boxes, what kind of ground lift cables could it try? The first ground loop i get is when i take a send from Gizmo loop 2 to Axe II's Input 1 (without anything else plugged into the Axe). Should i be going for a TRS to TS with the ground chopped off on one end? Or just a gorund lifted TS to TS? I already have Humbuster cables but these don't do anything for any of the Axe's Inputs that are causing the ground loops.
 
You should just use TS to TS cables with the ground disconnected at one end. Use one in each place you had an isolation transformer.
 
Sorry to be really thick but I don't understand how a TS - TS cable with the ground lifted at one end works. I though I would need both the tip and sleeve connected to actually carry signal as the sleeve functions as -signal and ground. What am I missing?
 
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