I could use some help with a "mystery" humm

I’m hoping to get some ideas on eliminating a hum in my system. It is an unusual situation, so I will try to be as specific as possible, without being to long winded

I have recently been replacing all of my single ended IC’s with XLR’s. My last component to switch over to balanced was my McIntosh MEN 220 room correction unit, to ARC pre-amp. I powered up, after switching over, and my previously quite rig now has a nasty hum, that is unacceptable. I tried various different XLR’s, to no avail. Once I switch back to RCA’s between these two components, all is good once again. I spoke with McIntosh, and some earlier models of the MEN had similar issues, but the problem has been rectified with the later models. I was asked to bring it to my local McIntosh service depot for inspection/testing. All checked out fine. The tech suggested I try a ground lift on the power line out of the MEN. I did this and it worked!! I proceeded to take every power cable out and check each one out for correct phase, as McIntosh told me that they have seen power cables miss wired quite often.

I am running 2 dedicated 20 amp circuits, each one delivering to separate Furman Elite 20PFi conditioners. I won’t bother listing all other components, as I don’t think it matters, but if anyone thinks it might, you can check on "My System" Bye the way, I have no television in my house, and my room is a dedicated listening room, so no other non audio electrical devices are present there. If anybody can suggest options, I’m all ears. I do not like the idea of keeping the ground lift in place. I should also mention that the amplitude of the hum remains constant, regardless of where the volume control is set, and the hum is gone when the MEN is removed completely. from the chain


Are you certain the hum comes from the MEN unit?

Have you tried the MEN ac into the other 20Pfi? 
Well, at this point I can't really be certain about anything. I have tried it plugged into the other Furman, and no difference. All my experimenting so far points to the MEN, but I'll explore any reasonable advice given. What is certain though, is that no hum exist with the MEN out of the loop, or with it in the loop with a ground lift plug no hum exists.
Crazyeddie - A few years back I experienced a hum when I connected a component that utilized a two pin plug.

When used with my amp, which which had a three pin plug, a loud hum was present.

I disconnected the component and powered it up without connecting it to the system. I then measured the differential between the neutral side of the output jacks and the mains outlet ground using a digital multi-meter .

I  found there was "noise"  i.e. a voltage could be measured.

A note about meters - depending on their design, an analogue meter may not show any reading whereas the digital meter has a high input impedance, which allows it to more accurately record even the slightest amount of noise.

The simple cure in my case was to attach a drain wire to the chassis of the component and attach the other end to the ground of the mains outlet.

However - If the component in question uses a power cable that has a ground pin - there may well be some problem that should be addressed by a qualified technician.

Like you, I tried various noise defeating devices without success,

I do not consider lifting the ground of any component a wise move - it's there for your safety in the even of component failure.

Not sure if it will help, but its something else to try - good luck

@williewonka  Thanks for the reply. My power cord IS a 3 pin, But you have given me an idea to try. It will be quite easy for me to try a ground line from the chassis, to earth, as my house main water supply line is in a cabinet directly behind my audio gear. I'll give it a shot when I get home tonight and let you know.


crazyeddie - I prefer to use ground on the mains outlet, but If there is a differential between the mains outlet ground pin and the water line - you have a more serious mains problem that should be rectified.
Have you tried swapping out the XLRs you've used for the MEN? I would assume so, but didn't see it up there.

@toddverrone Yes I have tried a few different cables. No change at all in the hum. All is quite when I switch back to RCA's though.

Even though the  MEN has been "checked out",  when it is connected via XLR it presents problems

Perhaps you could verify it's OK by doing the following using a digital multi meter
- disconnect the MEN from the system 
- power it up
- for each XLR input and output measure the differential (AC and DC) between the mains ground and the ground pin on each XLR socket 
- if there is any voltage there is a problem

Perhaps when it was "checked out" the techie only used RCA?