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How to eliminate system hum?

I have the following
Rotel 1090 amp
Hovland Pre-amp
Sony 777 CD player
Shahinian Speakers
I have this irritating hum/hiss when I turn on the pre-amp. The sound comes from the speakers when the pre-amp is turned on. If the pre-amp is off and the amp is on, the system is totally silent. It seems as if the amplifier is ok. It seems to be doing its job and is amplifying the crappy signal it is receiving.
Thinking my home electric was poorly configured, I had my electrician install a panel and dedicated lines for my system. The problem is now worse!
I don't think the pre-amp is to blame as I had the same problem with my previous pre-amp. I also have a new cd player.
I have read about "floating" the system ground by using 3 to 2 prong adapters on all system power cords. Is that what I should try?
If anyone has any ideas, I'd be very appreciative. Having $20k worth of stuff that sounds bad is no fun!
holzhauer
12 responses Add your response
judit
217 posts
 
If this is a ground loop hum created within your own system, it should go away if you float all plugs in your system EXCEPT one. You should have one component connected to ground; your interconnects ensure that there is a path back to ground for your remaining components.

If this doesn't do it, then your problem lies elsewhere. Is your system tied to video that includes cable? Cable boxes are notorious for introducing ground loop hum into audio circuits, if they are on the same line.

A final thought - flourescent lighting, electric motors, radio transmitters will create strong interference fields that will be picked up by unshielded wire and interconnects acting like antennas.
holzhauer OP
201 posts
 
Thanks Judit. I now have 3 to 2 adapters on everything but the preamp and the hum is totally gone! Ah sweet music again!
I guess this is a fairly common problem. But in 22 years of stereo ownership, I haven't had it. I'm thinking the 380 watt/ channel Rotel exacerbated the problem as it amplifies the living day lights out of everything that comes its way.
foreverhifi
229 posts
 
YOu only need to float the ground on one of the components to break this hum problem Just try the 3/2 plug addaptor on 1 different component at a time until the hum goes away...no need to "unground" all the plugs with 3/2 addaptors. The fact that all the components are connected, and at least one is grounded, this will keep your system safe and grounded throughout. No problem...
sean
6,231 posts
 
Try reading this thread and see if it helps. There are GOBS of other similar threads in the archives also. Sean
>

Noise, Hum and AC Polarity
a1126lin
70 posts
 
hi this is probably a dumb question. what does it mean to float the ground and what's a 3/2 adaptor.
i have two system. when i use system 1( mark levinson 336/380s) no hum but system 2 nak pa7 nad nak ca 7, big time humming. all ancillary equipments are the same ( speaker , sources ...etc ) why is that?
holzhauer OP
201 posts
 
Sean:
I read your entire noise hum and polarity post. You receive an A+ in my grade book. I think you qualify for the honorary Phd in hi-fi. How long have you been doing this?
P.S. The owners manual for the CAT SL1 ultimate had a similar discourse. Just not as detailed. I bought a VOM today.

A1126lin: 3/2 adapter is a $0.39 hi-fi component at Ace hardware! The female end takes the 3 prongs from your power cord. The male end eliminates the ground and has only two prongs.
Floating refers to having only one of your components hard grounded to the outlet. The others have 3/2 adaptors and ground via the interconnects.
sean
6,231 posts
 
Holzhauer: I'd like to take credit for the info in that post, but i can't. This info has been available via several different sources and i simply made it available here on Agon for those that may have never run across or heard of such things. While doing so, i tried to take into account that many people that frequent these forums are not technically inclined, so i tried to break it down step by step. Hopefully, doing so has made it easier to follow along with and might help others to solve a problem.

As to how long i've been into "hi-fi", i had my first "real" system when i was 13 years old and am now going on 39. I grew up with a Father that had owned a component audio system for as long as i can remember. As such, i had a bit of a head start and the fact that i'm technically inclined hasn't hurt one bit either : ) Sean
>
a1126lin
70 posts
 
thanks for the advice
i try the 3/2 adaptor on my nak ca7 preamp and it reduce the humming at least 50%. there is no humming coming from the amp. what else can i do to eliminate the humming completely.
holzhauer OP
201 posts
 
A1126lin:
Try 3/2 adapter on all 3 prong components except the pre-amp.
a1126lin
70 posts
 
thanks for the advice , it took care of the humming completely.
arcalim
1 posts
 
I checked all the plugs connected to the surge protector and there's only one with 3 prongs, yet I get the hum. Since the proctector has 3prongs and is the one connected to the wall outlet, can I use an adapter for the only one that's 3 pronged and will the system still be safely grounded?
holzhauer OP
201 posts
 
I was able to eliminate the hum and still have one ground path. The pre-amp is a good component to ground as it is centrally located. If the surge protector is the only path to ground then you could float all but one plug going into it. If the preamp went straight to the wall outlet,the surge protector can be be floated at the outlet without doing each input individually. I'm not an electrical engineer so I can't tell you if there might be a safety compromise. I can say the technique eliminated all hum from my system and I have had no problems.
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