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Rotel RB-1080 humm

Has anyone experienced a speaker Humm with the rotel rb-1080 amp as part of their audio/video setup? I recently upgraded my amp from the rb-1070(130w/per)to the rb-1080(200 w/per), and once the system was connected I noticed a loud humming noise from both speakers. Evidently, The Humm only occurs when the video (S-video or composite) is connected? Once the video cable(tested both S-video and composite) is disconnected from the DVD to PRE amp the humm goes away. As a test, I tried a swapping Dvd players and interconnects and the problem continued. At this point, I believe the cause of the problem is with the rb-1080 amplifier, because when I re-introduced the rb-1070 amp into my setup the Humming problem went away....any ideas? Thank you

My setup:
MF AC3r pre amp
Rb-1080 amp
Rotel 971 CD player
Rotel Line conditioner
Signal cable interconnects, power cables, speaker cables

rudd
7 responses Add your response
rwwear
2,846 posts
 
It is a ground loop caused by the video connection. Does the 1080 have a three prong plug while the 1070 does not? If this is the case a cheater plug should relieve the problem.
darrylhifi
498 posts
 
Yes , Their are some questions about the saftey of cheater plugs, however I used to own a Rotel and used a cheater plug for about two years because of this issue without a problem. The other possible solution is disconnect your cable tv connection and if the the hum goes away than a ground loop isolator is a safer way to go.
rudd OP
51 posts
 
As it turns out the RB-1070 has 2 prong's and the rb-1080 has 3 prongs? I will test the cable option as Darrylhifi suggested and If that doesn't work then I will try the cheater plug and post the results of both tests. Is there a specific cheater Plug that I should look for and where would I pick one up? ...thanks for all your responses guys!
darrylhifi
498 posts
 
Any cheater plug will do , available at most hardware stores and Radio Shack.
rudd OP
51 posts
 
I managed to speak to a Rotel tech and he confirmed that due to the 3rd prong in the rb-1080, that more current was drawn and in part can cause speaker humm. He Also mentioned that ultimately , my Cable TV may be root cause... so I removed my TV cable from my television set and the humm disappeared. It appears that the problem is directly related to the cable television. The recommendation to resolve the humm was to purchase an isolation transformer. I'm not sure how expensive they are but my ultimate goal is to get rid my speakers of the humm at a minimal expense without sacrificing audio quality. Would the cheater plugs still work given the problem is with my cable TV? if so, would
this negate the effects of my after market power cords?
nrenter's avatar
nrenter
765 posts
 
I had a similar problem when I owned a RMB-1095. The solution was to get a cheap filter for the coax TV cable (I used a power strip that had a coax filter built in). Worked like a champ.
darrylhifi
498 posts
 
Their are companies like Mondial that sell them for around $100.00, but if you search, you can get similar products for much less , try MCM Electronics for starters, type in the search , ground loop , it is a device that goes on your coaxial line between the cable coming out of the wall and your cable box. Cheater plugs are always a last resort {for saftey reasons } , however you can use one for a couple of weeks till you get a CATV ground loop isolator . The cheater plugs are ususally only 2 or 3 dollars.
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