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What to use for amp hum.

post #1 of 17
11/28/05 at 4:18pm
Thread Starter 
Recently bi-amped my system, and have a moderate to slight ammount of hum. Was wondering what everyone throught was the most effective for eliminating 60hz hum? I've done a lot of research, and found that there are several (Hum-X, Ebtech, DCI, Roll, etc.) small units to insert either in the interconnect path, or the power cord. Any suggestions as to what anyone else uses or thinks is best would be appreciated.
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post #2 of 17
11/28/05 at 5:01pm
Check here and see if that helps.
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post #3 of 17
11/28/05 at 6:08pm
Whoa! Good info there, John. And how'd you know I needed that, too?

I've had a minor hum that's showed up in my system ever since I rearranged my components and recabled everything. Only shows up in the center channel and only when
cable STB -> TiVo -> TV
..................-> AVR
paths are active. Based on that and the info linked out of that article I wonder if I've got a cable ground loop which was indicated as a real common one. Interestingly, the 60hz hum is in only the center channel in all 5.1 modes but is in both channels if stereo output is selected. Have to experiment and see if I can isolate the problem with that info as a help.
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post #4 of 17
11/29/05 at 5:49am
Do you have a CRT monitor within 10 feet?
That could make a difference. I eliminated mine with a sheet of metal for about $3 between my CRT and my amps
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post #5 of 17
11/29/05 at 7:09am
In addition to the very good link that John Garcia provided, there are similar products to the Jensen such as some from Calrad that perform the same function when it comes to your incoming cable for a bit less money. If you do a search under my name and the word 'Calrad' something ought to come up. I'd recommend installing that first. For hum induced as a result of your having connected additional amps, there are several approaches you can look into before you spend additional money. For example, you can try plugging everything into the same outlet or perhaps your surge protector. Some people have had varying degrees of success by attaching grounding wires between their equipment. It's very much a hit or miss proposition though. Finally, if you've got a 'Guitar Center' by you (most do), they've got a product made by EbTech called the Hum Eliminator. Money back and all that.
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post #6 of 17
11/29/05 at 8:50am
You can find a less expensive inline isolation transformer at www.partsexpress.com, which is similar to what Calrad offers.
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post #7 of 17
12/1/05 at 5:48pm
Okay guys. After reading the info here and elsewhere and some investigation I'm guessing that the cable ground loop issue is exactly what's going on. Here's the quick version of what I did in troubleshooting and the results:

situation:
coax--> cable box --(RCAaudio)-->TiVo---(RCA)--->AVR
........cable box --(s-video)---->TiVo--(S-vid)-->TV

-- only if the audio path that starts with the cable box is selected at the receiver is the hum audible
-- trying various things with what was plugged in where made no difference
-- disconnecting the cable coax from the set top box kills the hum
-- (here's one I didn't expect) disconnecting the S-video cable between the cable box and TiVo kills the hum
-- swapping to a different S-vid cable still had hum
-- swapping the S-vid for a composite cable still had hum

Sanity check please
To me this points pretty definitely to a ground loop involving the cable TV coax.

Did I miss anything or jump at the wrong conclusion?

Thanks in advance!
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post #8 of 17
12/1/05 at 6:05pm
Seems to me I've heard of isolation transformers that you can install on the incoming cable feed (before the cable box) that might resolve your issues. Other than that, I'd recommend a big, ugly switch that actually physically breaks the connection on both the cable signal and ground.

Leo
(Not, by the by, that I actually have cable. Never did, probably never will. The iso-transformer'll let you leave it connected, and also limit (or eliminate) the hum while you're actually using the cable feed.)

(Leo)
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post #9 of 17
12/2/05 at 7:35am
Actually the question in my case is whether the diagnosis seems correct so that I can order an inline isolation transformer and have reasonable expectation that it will cure the hum. I'm thinking (hoping!) it will but wonder if there's anything in my troubleshooting that indicates some other source of the hum is more likely.
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post #10 of 17
12/2/05 at 9:20am
There are two potential fixes. You seem to have determined that it is the cable, which would suggest the cable coming into the house is not properly grounded. When I had this same issue, I first ordered the isolation x-former and used it (worked), but I also called the cable company and told them what was going on and they *eventually* came out and fixed it.
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post #11 of 17
12/2/05 at 10:39am
Yeah, John, I thought of that too. But my experience with the Cox folks is not good at all. I would be a major challenge just getting to someone who will understand that a ground problem isn't a complaint about the soil in my yard!
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post #12 of 17
12/8/05 at 1:02pm
(To recreate the followup to this)

I'm pleased to report that the isolation transformer did the trick. Thanks to John G's link and a quick order:

http://www.partsexpress.com/pe/showd...number=180-075

Solved the problem. And silence is indeed golden.
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post #13 of 17
12/8/05 at 2:30pm
Congrats! yeah, tell me about it with the cable company...first they said it wasn't their problem then it took them over 4 months to fix the problem once they realized it was!
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post #14 of 17
6/17/08 at 8:19pm

Re: What to use for amp hum.

Hey Guys, I have a hum. . I had one right after I bought a used 3 channel Acurus amp a few months ago (200x3). After some searching I identified the hum to be within my comcast hd box. Still, there was no hum before the amp arrived. Regardless, I bought an isolation transformer from partsexpress.com and that solved that baby.

BUT...I have relocated my gear and no longer have Comcast HD. So it's not even hooked up at all. Hum is back. Arggh. I seem to remember that these Acurus amps, while excellent, are prone to this.

Seems like most of what I googled was for cable type issues like the one I had. Thoughts on what might be a solution. One thing, it's certainly the amp. I unhooked the cables/wire etc...and hooked them back to my AVR and the hum wasn't audible.

Thanks for any suggestions.
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post #15 of 17
6/20/08 at 10:03pm

Re: What to use for amp hum.

I solved my amp hum issue in a way that would probably make the bizarre audiophiles cringe...but it worked.
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post #16 of 17
7/1/08 at 5:22pm

Re: What to use for amp hum.

If the cable company doesn't fix the ground problem soon enough. Just ground the cable splitter that the incoming coax is connected to. problem solved!
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post #17 of 17
7/1/08 at 8:54pm

Re: What to use for amp hum.

I don't think I saw this in any of the replies, I may be wrong, but I thought I would mention it for future reference. This might not be as cheap of an alternative to a isolation transformer, but might do a similar job, if one would look into a power conditioner, which are use a lot in professional audio recording to eliminate hum. The most often occurrence is in buildings or houses with older wiring. I'm not sure how a isolation transformer works, but the use of a power conditioner is one of the many things I've learned in my schooling in audio and TV production. One may find these at most any Pro audio/video store.
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