Ground Loops

E

EZP

New member
Hi all,
This is my first message on your forum and I hope you guys can help me.
I recently bought a G-Major (a guitar multi effect proccesor) which I connect directly into my mixer. As both devices are earthed, I heared ground loop hums. This was fixed by cutting the earth wire from my G-Major. But this device is installed in a 19" rack along with my headphone amp. This amp is connected to the mixer thru 6 channels. When I plug in the amp, the hum returns.
Should I cut the earth wire of the amp aswell? Or should I use 8 DI boxes? Are there any cheap and good audiotransformers to isolate the grounds from eachother?
Al Ground loop fixing ideas are welcome!! Thanks!
 
All equipment (G-Major, mixer, headphone amp, PA amp) come from the same socket (thru extension cables and splitters). Is this helpfull in any way?
 
Saw simular problem recently where I was getting some hum and shocking mics.

All were plugged into the same plug expander into one socket.

I replaced the plug expander with a product called

The Isolater from CompUSA. ~$69US

It has much better ground and power circuitry and isolates crosstalk between devices.

I think CUSA has a 14 day return policy. Might be worth a shot.

I assume you have tried different plug to ensure your plug is properly grounded.
 
I don't think it's in any of the mains cables. I used an old Zoom 9030 (don't buy it if you want reverbs, arg!) with exatly the same cables, both audio and mains and I never had a problem. I think it's becasuse my Zoom uses a wall wart adapter for his DC power, while the G-Major (you've gotta buy this if you want reverbs, hmmm) has an internal power supply with 3 lead going in. So if think I can solve it using transformers, uncouple-ing the output from my G-Major and the input of my mixer. Is www.Lundahl.se any good? Does anyone know where to get these on-line (just for a price check).

Thanks again!

Ezp
 
PUT THAT GROUND BACK ASAP.... you're gonna electrocute yourself that way!

Ground problems are tricky to sort out, because you need to find out if its a true ground loop issue, or if the hum is inducted into the cables somewhere....

The worst thing to do is yank the ground -- if there's a problem, YOU'LL become the path the electricity decides to flow thru (since YOU'LL be the easiest path for the flow to travel) BUT... if you want tinged hair and a funky new hairstyle, forget what I said.

Disconnect your unit from everything.... determine if it has a hum without being connected to any other gear (via headphone outs!).

If it's clean, then the source of the ground loop is in the combination of your rig...

Good practice tries to tie all the grounds to a common point.... if you don't have too much gear, try powering it from all the same source (up to 15 amps or gear on a circuit.)

You may need to disconnect each peice of gear and reconnect it one by one, in an effort to see which unit causes the hum.

Once you find one or more culprits, use a audio isolation transformer (such as EbTech's Hum Eliminator) to isolate the audio line.

Use nylon 10-32 screws and rubber O-rings to mount your rack gear and isolate their chassis' from the rack rails.........

Like I said, deducing a hum issue is pain, and is time-consuming, but you can lick it given patience.

Also, mixing balanced and unbalanced cables/gear without paying attention to proper interfacing of this gear will cause issues. Some balanced gear electronically accepts unbalanced connections, others do not...

Good luck.......

Bruce
 
Thanks for your input Blue Bear Sound!

Not to put you off or anything, but I know what I am doing with the grounding of the individual devices (I don't want to be showy, but I'm an educated eletrotechnical engineer, in 6 months). True, it isn't the safest way to improve the sound, but it worked (not anymore, that's why I'm here).

I double checked the manual, and it states that the outputs (as well as the inputs) are balanced, but work properly with unbalanced cables.
This is from the manual:
Note!
The analog Input and Output connectors on the G•Major
are balanced 1/4” jacks. Optimal connection to balanced
equipment is achieved using balanced cables.
However most guitar equipment is NOT balanced and
you will generally have no problems using standard
mono-to-mono cables as illustrated below.
Click to expand...
My mixer doesn't have balanced line inputs anyway.

I'm allready getting all my power (for the effect, mixer and amp) from one outlet, so that shouldn't be it.

I don't think it's my rig, because with my old Zoom 9030 it had no problems (the 9030 used a non-earthed power supply, which fed normal 0 and 12 (?) volts into the device).
But at home, I don't have anything earthed. That results in humming even when only the mixer is connected to a mic and a headphone, BUT when I earth any device in the chain with my finger, the hum is gone! Conclusion: at least ONE device should be earthed.

So the only thing left is those EbTech's Hum Eliminators. But these babies are $74.95 each! Are there any cheaper alternatives?

Again, I DO appreciate any input in this thread!! It's just that I am working on this problem for a while now, trying everything without purchasing anything (I am only a poor student, and I had to save up far to long for the G-Major).

Thanks!!
EZP

ps. I AM getting those nylon screws!
 
EZP... I hear ya - but if you do cut the ground, the electricity won't look at your electrical engineer diploma before it chooses to flow through you instead of the gear in the event of a problem! ;)

Cutting the ground is a dangerous practice - period, no matter what credentials anyone has!
There are better and safer ways to deal with ground problems.

Cheers,
Bruce
 
In terms of isolating rack gear - in addition to nylon screws and rubber O-rings to isolate the units - I also forgot to mention putting thin rubber matting between devices so that their chassis' are not physically contacting each other.

Bruce
 
Good idea! Any tips on the best stuff I can use for this? CAn I simply cut open an old bicycle inner tire, what do you use?
About the rings, should I use 2 per screw (one in the front, one at the back) or is one (at the back of the frontplate) sufficient?
 
ps. My 'hottest' device is a heaphoneamp consuming 40 watts, so my rack shouldn't get verry hot inside...

EZP
 
Before I bought a pair of Furman Isolation Transformers (IT-1210s) I used to use the anti-static workspace sheets available at electronic component shops in between each piece of gear (of course, not if there's ventilation holes at the top!).

Whatever you use needs to be thin, otherwise you will have spacing problems fitting the gear in the rackspace.......

With the Isolation Xformers, my rig is silent so I don't need to worry about it! (BTW, that's a $2K solution...)

Bruce
 
Bruce,
Thanks for the tips, but you realize that if I were to buy such a Furman IT-1210, that I would double the value of my entire rack? I think the IP2B would be a more suitable sollution, and I'll save $5 compared to the humeliminator!
 
Follow up question:

My G-Major has balanced line-outs, but my mixer does not. Can I connect the two using such a cable:

G-Major Output------------------------Mixer Input

Signal + -------------------------------- Signal (+)
Signal - --------------------------------- Ground
Ground ------ Unconnected

I can easily convert the output range of my G-Major, so a 4 dB increase is not a problem and can be delt with.

EZP
 
To wire a balanced to unbalanced cable:

Tie neg- and shield together, pos+ stays as is...
You will get a 6db (at +4dbU) drop in signal level doing this (since you are losing half the balanced signal)...

See this link for more info....... they spell out all connection configurations.

http://www.rane.com/note110.html


Bruce
 
Blue Bear Sound said:
In terms of isolating rack gear - in addition to nylon screws and rubber O-rings to isolate the units - I also forgot to mention putting thin rubber matting between devices so that their chassis' are not physically contacting each other.

....I used to use the anti-static workspace sheets available at electronic component shops in between each piece of gear
Click to expand...
Bruce,

This is very good advice to isolate all of your chassis, but anti-static sheets are about the worst thing to use. Anti-static material is specifically designed to be CONDUCTIVE. But it's not usually highly conductive, so it would be like connecting your chassis together with resistors of few 100 to a few 1000 Ohms. Not a good thing.

Better to use any light colored plastic. Black plastic sometimes contains graphite which makes it somewhat conductive. Paper is also a good insulator.

Reminder to all - Always be on the lookout for Fire hazards in your studio as well.:)

barefoot
 
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