Hope this helps!
Dealing with Hum in Counterpoint Gear
Lose the Ground Loop
All Counterpoint gear was manufactured with three-prong AC cords. This is for safety: if something were to fail in a piece of gear, potentially dangerous currents would go to the AC receptacle's ground, and not into a person touching the equipment. Few manufacturers took this step. Counterpoint did it not because Counterpoint gear was particularly prone to faults like this -- the truth is, that in nearly 20 years of manufacturing, no piece of Counterpoint gear ever failed in such a way that could result in a "live" chassis -- Counterpoint did it for customer safety.
The safety benefit of having even one component earthed extends to all the other components in the system because they are all connected toether by the interconnects. So if one component faults, the dangerous currents would travel through the interconnects to the earthed component, and drain safely away through its AC cord.
But if more than one component has a three-prong AC Mains cord, there's a risk of creating a system hum or buzz audible from the speakers. Earthing more than one component causes a ground loop -- a condition where there is more than route whereby the grounds of the components are connected together. Your components are already connected together through their interconnects. If you also connect them together through the third prong of their AC cords, you get a hum. Its usually not very loud, but it is also usually quite audible, and an indication that ground currents are flowing around where they needn't be.
The solution? No, not a line conditioner -- they clean up your power but don't break ground loops. And it doesn't matter how many dedicated lines you had your electrician bring in, or whether you have hospital-grade outlets in the wall! What you need is to have only one component three-wire connected to the AC receptacle or line conditioner. All other components should be two-wire connected only.
All the other components with three-wire AC Mains plugs need to have ground adaptors ("cheaters") installed on their AC plugs. These useful
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Use a grounding adaptor on every three-prong AC cord except for one.
little gadgets can be found at hardware stores and places like Radio Shack. Put them on every three-prong AC cord except for one. Let that one earthed component provide the system ground and lift all the other grounds. Don't connect the little green wire or green lug on the adaptors -- that'll defeat the purpose.
Once you've eliminated the ground loop you'll have a safe and quiet system.
(I think that the reason that other manufacturers don't routinely install three-prong AC Mains plugs was for their convenience: they didn't want to deal with customers calling to ask why they have a hum in their system.)
If You've Done All That But Still Have A Problem . . .
. . . do you have a TV cable hooked to your system?
Perhaps through a VCR? That's another, second, ground. That TV cable is also grounded, but it's not a real safety ground. You wouldn't want to count on it in the event of a power fault.
If you have cheated all but one of the AC plugs and you still have a hum, you can disconnect the TV cable and see if the hum goes away. If it does, then you'll need to isolate that cable ground. There are a few ways you can go about isolating the system from the cable TV ground:
Mondial makes a cable isolating device call the "M.A.G.I.C." - Modial Antenna Ground Isolating Circuit. It's available from the Audio Advisor at www.audioadvisor.com, catalog number MONMAGIC. This device also adds lightening power surge protection to your incoming cable. It is pretty expensive for what it is.
Or use the VR-1FF "Iso-Max" cable TV isolator by Jensen Transformer ( see http://www.jensen-transformers.com/vr1ff.html).
The electrically-clever can make their own by connecting two 75-ohm-to-300-ohm transformers back-to-back.
. . . or do you have your equipment in a metal rack?
If more than one component is in electrical contact with a metal rack, you are providing a second ground path between the components -- the rack itself. You need to insulate the components from the rack so that the only ground connections between components is through the interconnects.Professional musicians and recordists use racks a lot and they have to deal with this problem all the time.
You can check for this condition by using an ohmmeter to see if the chassis and the rack are electrically connected: If you remove your interconnects but still measure continuity (low resistance, under 10 ohms) between your components, your components are probably still connected through the metal rack. The connection is probably through the screws that are being used to fasten the unit's front panel to the rack. You must isolate the chassis from the rack.
One easy way to take care of this problem is to use "Humfrees Rack Isolation Tabs" from www.musiciansfriend.com.
As they say, "Kill those ground loop hums by using Humfrees to electrically isolate rack unit cabinets from each other and from the rack. Easily installed without removing units from the rack."
