Installing RB-1080 and getting hum

[will1066]

Hi everyone,

I'm in the process of installing the RB-1080 in my system and after getting the line-level and speaker connections done and hitting power, I am getting a loud hum in both of my main speakers. Playing a CD, I got music so my guess is there's nothing wrong with the amp and that I'm getting a ground loop hum(?). I have not had this hum before at all when powering all of my five channels via the RMB-1075. All my stuff is plugged into a TrippLite Isobar: CD player, universal player, old tube TV, analog cable box, etc. I turn on the 1080, and the hum starts and when I turn it off, the hum slowly fades away as the protection light slowly dims. Does it matter if I have the 1080 on the floor and directly under my A/V rack (I don't have a rack slot for it)? Can you folks lead me in the right direction? Thanks so much.

[art vandeleigh]

why dont you try and isolate the power supply for the 1080. try and plug the 1080 directly into the wall outlet and see if that solves your problem. being under your av rack should not cause this problem, but try and move it to a different location. is this unit new? i have heard of the 1095 huming but never the 1080. good luck

[will1066]

Art,

Yup, it's new. I moved it from the floor under my rack to a shelf on the rack and the elevation made no difference. I was thinking what you suggested - plugging it directly into the wall outlet but the way my system's set up in my room, I need a much longer power cord than the supplied one to go from wall to my gear nest. My TrippLite serves as a multi-outlet extension piece from my wall in addition to surge protection and filtering.

To everyone else, do you have any other suggestions or ideas? Thanks.

[Andrew Pratt]

Try running a long extension cord and see if that fix's it. If it does the only real solution is to run another properly grounded power cable to the gear rack. While you're at it you should likely make it a 20 amp line and run both the 1075 and 1080 on it.

[will1066]

Andrew, I don't have a grounded extension cord so I plugged my PS Audio Ultimate Outlet directly into the wall outlet and then plugged the 1080 in there while the rest of the gear was plugged into the TrippLite, which was plugged to the wall outlet. So I isolated the 1080. Still a lot of hum. I unplugged the TrippLite and left only the UO plugged into the wall outlet; still hum. Some time earlier, when I was still experimenting and playing around (read: panicking), by pure luck, I was just wiggling some wire and cable and the hum went from soft to none. But my amp wasn't in place so as soon as I tried to move the amp, I guess I shook the wire and cable out of their "magic spot" and the hum resumed. Since then, I've unplugged everything and started over, trying to keep all power cords away from interconnects and speaker cable. The wiring is now all neat and tidy but as long as the 1080 is on, the hum is omnipresent.

[Aussie Geoff]

Will,

I too had a RB-1080 with hum. Now there are many and varied causes of hum (mostly ground loops), however once these are eliminated there can remain certain situations where any of the Rotel RMB-1095, RB-1090 or RB-1080 amplifies (all have balanced inputs and 3 pin plugs) can produce annoying hum. The test for this is to unplug everything from the amplifier except the speakers and have the amplifier plugged straight into the wall. If with no input and plugged straight into the wall the hum goes away, then you have ground loop hum from somewhere (usually coming in thorough the RCA leads from the pre-pro from somewhere like a satellite or TV or cable antenna (Sometimes coming in through the ground pin itself in the mains from another component). In which case follow the normal (well documented) ground loop isolation techniques.

However if you get hum, with no inputs then the amplifier is picking up noise from the mains. In which case you firstly need an electrician to check that you don't have a ground current flowing through the earth in your house or apartment (faulty earth in your house or a neighbours. If the electrical says "no ground current" then try a cheater plug (available from USA hardware stores – it’s a 3 pin socket plug with a 2 pin plug). 99% of the time that will make the hum go away. If it doesn't you have a faulty amplifier. Now if the hum goes away with a cheater plug you have a dilemma – most people are happy and just go back to listening to the difference a great amplifer makes to their system, however some are concerned over disabling the ground, in which case you need to return your amplifier and try sample or another band.

Now, there are lots of different ways of doing a ground plane in an amplifier. Rotel did it a certain way in all there 3 amplifiers with balanced inputs (RMB-1095, RB-1090 and RB-1080). This way is susceptible to certain types of noise / current imbalances in the mains and can (in a small % of cases) drive people mad trying to track down a ground loop that isn't there.

Some other amp manufactures with balanced inputs had the same issues (e.g. some earlier Byston amps) and they changed their ground plane scheme to address it. I suspect that Rotel is in the process of doing the same thing. I had an intractable problem with RB-1080 hum (just like yours sounds) that only a cheater plug would fix (swapping 1080's from my very helpful dealer didn't make any difference). Now Rotel have just come out with a newer model 1080 (recognisable by the dual speaker terminals for each channel. This has a different grounding scheme than the older models, and I've tried one in my set-up and NO HUM - YES YES YES )

I'd be interested to know if your 1080 is one of the newer ones with the changed ground plane. If it is I'd be surprised if you haven't got just the normal ground loop hum in through the RCA leads problem!! If it’s an older one and you are getting hum with no inputs etc, then ask your dealer for a new model and I think your problem will be solved.

Regards

Geoff Costello

[ejfiii]

Will,

Just for giggles, remove the cable coax from the cable box and get it as far from the 1080 as you can.

I bet dollars to doughnuts that it will go away and you have an improperly grounded main cable feed at the side of your house. It is possible that it was never bad enough to cause a problem before, but the addition of the 1080 may have ben the proverbial straw that broke the camels back and started the hum feedback. I spent almost 3 months chasing a hum problem in my system that I KNEW the whole time was the cable line. It still took me almost 3 months to finally fix it.

I may be wrong, but don't know what else it can be. Unless you just got a faulty 1080.

Good luck,

E. J.

Edit: Geoff and my posts crossed and his seems like a much more reasoned and scientific explanation. I too agree with trying the cheater plug first and see if that does it. At any rate, good luck.




My HT

[will1066]

Geoff and E.J., thanks for your help.

Geoff, I guess I got an older version of the 1080. I unplugged the interconnects from the 1080 and left only the speaker connections on and the hum became minimal. I then followed E.J.'s advice and disconnected the coax cable line from the cable box. As soon as I disconnected the cable line, the hum was completely gone. I didn't even need to move the line away from the A/V area.

So how should I proceed? Address the cable line (w/ cable operator?) or exchange to the new-version 1080? I don't wish to use a cheater plug because of disabling the ground and its dangers.

[aud19]

I'd take the 1080 back to your dealer and get the newer version to start with. Hopefully that will fix the problem. If the cable feed still causes a problem with the new amp...go find that tall building...lol. Seriously though, I've heard that pulling your cable feed out of the jack slightly so that the centre pin is still connected but the outer shield (ground) is not, that it disconnects the ground loop (..obviously :roll: ...lol). The only problem with this solution is that your cable feed might have a tendency to wiggle loose if any of your equipment gets moved . Maybe some of you other kind folks have better suggestions..? You could also try calling your cable provider and see if they have any solutions (though we know how helpful they tend to be). (I can say that because I used to work for one )

Jason




Need a new display? Questions about new display technologies? Visit RPTVs, plasmas, and other monitors @ HTguide

[Azeke]

Will,

I would definitely request the newer version, after all it's your money.

This must be most disappointing, you have my sentiments . I haven't received my RB-1080 yet, but when I do I will ensure it is the latest version (thanks all of you).

Now I feel somewhat apprehensive with running the RMB-1095 with the RB-1080. I guess I'll find out soon enough.

Well now that you have isolated the problem, is it worth the upgrade for stereo, (excluding the hum issue of course)?

Awaiting your opinion and good luck,

Azeke

[jimmyp58]

Will:

Please respond to the e-mail I sent you.

Thanks...

Jim

[will1066]

Thanks again for the replies. Jason, I did as you told, making a minimal-contact connection with the cable feed and that prevented the hum. The picture is a little weaker, of course, but it's great as a temporary stopgap. So, thanks for that suggestion. I got a recommendation for a product called ISO-LinQ from MIT that is supposed to break the circuit in the cable line that causes the ground loops. I'm going to try this first before I return the 1080.

As you can understand, I've only listened to one song (that I'm really familiar with) on the new amp. Based on that, I heard nice improvements in clarity, bass, and imaging.

[Aussie Geoff]

Will,

If disconnecting the Cable feed makes the hum go away completely then you do not have the problem with noisy mains. (People with this problem get hum even with nothing connected to their 1080 / 1090 / 1095 RCA inputs.) Your hum is coming in via the earth shield on your cable which hasn’t been properly grounded either in your house or somewhere nearby. Once in the system (your cable box) it will spread either through the RCA lead into your pre-processor and then down the RCA leads into the 1080. With some cable boxes it can also spread into the mains (the earth wire normally) creating a milder hum (which could well be what you have left when you unplug the RCA lead from the 1080 and still get some hum). Basically the 1080 being earthed allows the ground from the cable to finally leak away, unfortunately coming in through the RCA leads means you hear it first! This will apply even to the latest 1080 (it will apply to ANY grounded amplifier since the ground provides somewhere for the earth leak to go to)

There are some good cable ground loop isolators from Radio Shack that you can self install in the cable box OR as you have ordered a line isolator transformer. This will fix the problem once and for all and is the best way to go. Only if you still have a residual hum after all this would I then consider the mains noise issue and trying a cheater plug or new model 1080 (i.e. the new model won't fix the ground loop problem from your cable).

Try these links for more information:

http://www.epanorama.net/documents/groundloop/index.html

and

http://www.smr-home-theatre.org/Ground-Loops/

Regards

Geoff Costello

[espo]

The dedicated 20amp circuits for my A/V components as well as my cable TV are properly grounded to a common grounding stake. I still got a hum when I added a new amp with a grounded plug.

With multiple paths to ground, even the same ground, there is always the potential(no pun intended) for a ground loop.

I solved the problem by adding a ground isolator to my cable TV before it connects to the A/V. I used the Jensen VRD-1FF, since it has a broad range for digital channels- 5-1300. I purchased it from Markertek for about $50.

[will1066]

Thanks again. You've all been the most helpful. Geoff, I'm going to read up on the links you provided. Actually, I had that bookmarked long ago because I knew I'd run into a ground loop problem eventually.

[ejfiii]

Hey Will, when are you going to send the doughnuts?

Seriously, you should be able to fix this the way I did by either yourself or the cable company coming out and fixing the ground. It was simple once I knew I what to look for, but each house wiring system is different.

If you dont want to spend any money, then go out to the cable box on the side of your house where the cable first comes into the house. There should be a splitter there. On that splitter should be a single stand wire connected to a screw terminal. That is the ground wire. It looks different than the coax wires. Anyway, trace that wire out to the other end and see whats it connected to. In my case, it was connected with a screw on bracket to the main house earth ground next to the main electrical panel. I wiggled that fitting, and it fell off. I tightned that fitting to the house ground wire, in addition to tightening the screw terminal on the outisde splitter, and bye bye hum. It is really that easy.

Now, your cable installer could have been a lazy lump and not installed the ground wire at all. If thats the case, then either you should install one as I described above (another popular place to connect the ground wire is the cold water pipe), or call the cable company back and bitch until an installer comes out that knows what he is doing.

As far as an isolation transformer is concerned, I have one in my pile of HT crap in my basement. This was the first thing I tried and yes it cured the hum, but it also cured me of the nice HD picture I had. So be careful with signal loss on anything you are going to add to the system. This is why I went back and fixed the ground the right way myself.

If you want, I would be happy to send you a christmas present so you don't have to buy one and since mine is just sitting in a pile of wires in the basement.

If you want it, feel free to email me at: internet@feulner.us.

Hope this helps.

E. J.

PS - as others have pointed out, your amp is probably fine, I would leave it alone.




My HT

[will1066]

E.J., do you prefer Dunkin Donuts or Krispy Kreme? :LOL:

I took a look at my cable line outside and it appears to be properly and tightly grounded (to a water pipe). I am waiting for the line isolator from MIT to come in the mail. I hope it will be the remedy but I will look out for a softening of my cable TV picture. But to be honest, I'm not very picky about my picture but I guess I will change when I graduate to HDTV. E.J., if the MIT product doesn't work out, I'll give you a buzz (pun intended, haha).

[will1066]

Just want to say that I went with the Jensen VRD-1FF and it eliminated the ground loop from the cable TV line.

Silence is golden.