Ground Loop Problem

I'm having some problems with a contant hum through my rig and an engineer friend of mine said it was probably a ground loop. It's not the guitar(s) or anything else in the room.

I'm running three US rack units and two UK ones so there are two step down power convertors in the mix (the US gear uses high wattage so the cables are grounded ((has the third cylindrical pin)) - I'm in Ireland so we have the same power supply as the UK. I'm pretty sure all of the UK cables are also grounded.

I've been told that I should only have one unit grounded in the rig... is this true? If so, is it safe for me to use ungrounded cables for particular units when the manufacturers specify grounding for safety?? If so, which unit should be grounded???

Here's the setup...
Triaxis (US)
Eventide Harmonizer (UK)
Noise reducer (UK)
Mesa Simul-Class poweramp (US)
Delta 1010 soundcard rack (US)

I know nothing of electronics or power supply jargon so if you know how to solve the problem, pretend you are talking to a child!
Cheers,

Get a power conditioner. It "cleans" the electricity coming out of the wall and effectivly eliminates ground loop problems. It is essentially a rack unit that looks like a power strip on the back. I don't think they are too expensive but you'll get what you pay for.

http://www.musiciansfriend.com/srs7/g=home/navigation?q=Power+Conditioners

Are the step-downs for that US gear autotransformers, or are the windings isolated?

Your system must have a single-point ground, or else there will be lots of noise problems. You've got all sorts of series/parallel ground paths caused by the interconnections between components that are running off diferent power lines. Get your engineer friend to show you how to clean up your grounding.

Not sure what 'windings isolated' means... they look like transforers, black boxes with a US plug in on one side and a UK plug out on the other... my knowledge of things electrical is pretty bad.
As far as getting a Power Conditioner goes, would that solve the problem of having combined US and UK power supplies? I emailed Furman a bunch of times but I've yet to get a reply on whether any of their products would suit the bill...

An autotransformer is a single coil of wire wound on a core. The high voltage is applied to the entire coil, and the low voltage is tapped off between one end of the coil and a point near the mid-point of the coil. This can be dangerous, because there is a direct connection between the input and the output.

A proper transformer will have two coils wound on the same core. One coil will have roughly half of the number of turns as the other coil. With the high voltage applied to the bigger coil, the smaller coil will have a smaller voltage available at its terminals. This is a safer system, because the coils have no direct connection between them. They are isolated from each other.

As far as I know, most 'power conditioners' only have surge suppressors in them, to prevent voltage spikes from damaging equipment plugged into their outlets. Isolation transformers with step-up or step-down voltage selection would be quite expensive.

This is what one of the more costly conditioners said it could do.

The quality of AC power has been so poor for so long, most musicians have no idea how great their amplifiers could really sound. When the AC power factor is poor, amplifiers sound muddy because their power supplies can't deliver when pushed. The scream and cry from a guitar loses bite and harmonics, basses lose their punch and weight, keyboards sound nasal, losing clarity, attack, and extension. The answer is Furman's Power Factor Pro.

The Power Factor Pro's Clear Tone Technology actually lowers the AC line impedance supplied by your wall outlet, while storing energy for peak current demands. In fact, there are over 45 amps of instantaneous current reserve in the Power Factor Pro. Additionally, Linear Filtering TechnologyTM dramatically lowers AC line noise to unprecedented levels in the critical audio frequency band. What does this mean? Just plug in your current starved amplifier, crank up the volume, and listen to the dynamics, harmonics, and clarity you've been missing!

Additionally, the Power Factor Pro is the most comprehensive power conditioner ever created for the serious musician. Maintenance free - Series Mode Protection guards your equipment from voltage spikes that can damage your clamps at 188 Vpk, 133 VAC RMS even when tested with multiple 6000 VAC - 3000 amp surges! The pro level over-voltage auto shutdown circuit assures you will never see your prized amplifier go up in flames due to a sustained voltage overload.

The Power Factor Pro R has a generous 12 amp RMS capacity, a convenient 20-segment AC voltmeter, one front and 8 rear AC outlets. Rear BNC connector allows connection of standard 12V gooseneck lamp for rear-panel illumination, all in a single-rackspace design.


Now as for the Euro and American plugs. That is beyond me. I guess I could say get a Euro conditioner and an American on and wire accordingly but I can't say with any certainty if this would work. It seems to me that maybe you could find a some step downs with the same capability as these conditioners but again I don't know.

That's something I would very much like to test in my lab.

I really would like to research the efficiency of some of these conditioners myself. We used a couple at a studio a while back and they seemed to work ok. They were used for the rack recording stuff more than the guitar rack so who knows.