Speaker Hum Revisited (Again!) (1 Viewer)

[Wayne_T]

I simply used a cheater plug and for the amp and now the hum is gone.

That's a good troubleshooting technique to confirm that there is a ground loop problem, but please don't recommend it as a permanent solution to the problem. Removing the chassis ground connection on power supplies with three prong plugs exposes the user to potential electric shock hazard. Yes, its a quick and easy way to fix the problem, but all too easy to forget that way, and a future malfunction could result in a "hot" chassis.

Just call me "Elmo" today.

Cheers

 

[Paul Clarke]

Guys, guys,
You need to chill. I know you are well intentioned but PLEEAASSEE! There ARE OTHER ways of affecting a ground situation without the three prong, especially in this case...AV equipment which is not likely to be moved around a great deal. Hell, you can ground your whole D**n rack if you want to...and not use a single three prong. For sure, the ground plug is the simplest means to this end...but sometimes you just have to improvise.
You're right though on the brevity of my answer. I was perhaps assuming too much of Vlad. I'd be willing to bet he knows what the adapter is...just never heard that specific nickname applied to it. There I go assuming again.:b

 

[Vlad D]

Anyway, if the hum is unaltered by the volume setting it suggests to me that the hum is introduced after the amp stage. I would first check all connections for frayed wires. I would also swap around cables just in case one of them is bad. A bad wire could have unpredictable results.

Mike, I'll re-check all my connections when I get home. But I don't think that's the problem. My speaker cables are relatively new (6 months old) and my RCA connections b/t receiver and amp are brand new. But, it never hurts to re-check.

Thanks guys.

 

[Vlad D]

Update. Still have the hum! I changed my interconnects today. Bought some shorter cables. The other ones were too long and crossed some power cords. I figured maybe that was the problem.....nope. The problem has to be b/t the receiver and the amp. If I turn the receiver off and leave only the amp on the hum is gone. Turn receiver back on and its back. And this is with all sources turned off.

 

[Mike Veroukis]

Vlad,

Have you tried this test: connect the receiver and amp like normal but disconnect absolutely everything else from the receiver including any other speakers (that is, any speakers you have connected to the receiver, keep the ones on the amp). Keep both the amp and receiver on, does it still hum? If yes, I would consider trying a different amp. What happens when you use the receiver's internal amps? Does that cause a hum???

Have you tried a different receiver or amp?

I remember when I was trying to diagnose a hum problem I used a discman as a pre-pro and fed it straight into an amp's input. The hum went away of course as a walkman could not possibly introduce a ground or phase hum. Not sure this would be useful to you, but something to think about.

- Mike

 

[Vlad D]

Mike,

The receiver's internal amps did not hum. This is the first separate amp that I've tried. Just recently bought it. I thought just turning off the sources would be enough. I'll disconnect them all and see what happens.

 

[Mike Veroukis]

Vlad,

Turning them off may not (in fact, should not) make a difference. For example, I had a hum when my computer audio outputs were connected to the receiver. Why the computer? Well, I have a cable modem which is copnnected to the cpmputer. Even though the cable modem is not connected to my receiver directly, the ground loop hum went through all the computer and ended up at the receiver. Basically, if anything at all connects the two units it could cause a hum, even if that's just you touching the two units. So yeah, it's important to physically disconect everything.

So yeah, try disconecting everything from the receiver (except the amp of course) and see what happens. If that doesn't fix it we atleast eliminate a bunch of possible causes.

- Mike

 

[Steve Zimmerman]

Listen carefully... USE THE CHEATER PLUG FOR TROUBLESHOOTING to find out if you have a hum caused by a ground-loop problem. If you *do* have a grounding problem then you won't waste your time replacing cables, amps, etc. Not all grounding problems are caused by cable TV.

The cheater plug is about one cubic inch in size. It is a small adapter available at just about any hardware store that has holes for a three prong plug on one end and a two prong plug on the other.

Again, USE THE CHEATER PLUG FOR TROUBLESHOOTING.

And if it sounds like I'm yelling... Well, I am.

--Steve

 

[Mike Veroukis]

Yeah, Steve's right, but HE DOESN'T HAVE TO YELL!
You don't NEED a cheater plug, but it makes it easier. I solved my hum problems without one.
- Mike

 

[Gilles Cyr]

Hi Vlad.
I had hum in my system a while back and could not figure it out.
So I grounded the casing of all the units in turn to an AC box with a zip chord until I found the culprit. Worked fine.
Oddly enough, the same system, configured differently, produces no hum.
Home this helps.
Regards

 

[Vlad D]

Update. I disconnected everything from the receiver. Only thing connected are the pre-outs to the amp and subwoofer. Hum is gone. But now I hear a tiny hiss. It was probably there before but just didn't hear it over the hum.
So now I'll connect each device one at a time to find the culprit.
Also, I'm going to buy and USE THE CHEATER PLUG FOR TROUBLESHOOTING.

 

[Vlad D]

Update. I found the culprit!!! It's my stinking VCR! I connected each device separately: STB - OK, DVD - OK, TV - OK, VCR - HUM!!! So, I really don't use it very much and don't need to watch recorded TV shows in surround. If I connect the VCR straight to the TV and not through the receiver should that eliminate the hum?

Also, the hiss is present during the hum. And, I think I may have had it before I got the amp. I'll have to disconnect my speaker from the amp and reconnect to the receiver to check. Just don't have the time now, have to get ready for work.

 

[Mike Veroukis]

Vlad,
Good job! So it seems it was a cable ground loop after all. This is usually fixed by using a ground loop block. This is how I fixed my hum problem. You can buy one of these at radioshack for about $5. It's like an adapter that you "splice" into the coaxial cable as it enters the house. The ground loop block will need to be connected via wire (any wire will do) to a proper ground (breaker, fuse box or any pipes connecting to ground).
You can find tons of into on this if you do a search on "ground loop block" as this topic pops up every few weeks or so.
Take care.
- Mike

 

[Marvin]

I also got a Parasound 855 from Ubid. I received it last week but haven't set it up yet since I need to finish putting my new rack together first.

But I tried it out last nite and got the same hum that Vlad described. When I disconnected the TV cable from the cable outlet, the hum went away though I was left with a lower hiss, as others have described. I don't know if this is because there are other cable outlets in the house that I didn't disconnect or if it always happens with amps, or this model amp or whatever.

So I guess I'll pick up a cheater plug before I officially set up the amp.

This is how I fixed my hum problem. You can buy one of these at radioshack for about $5. It's like an adapter that you "splice" into the coaxial cable as it enters the house. The ground loop block will need to be connected via wire (any wire will do) to a proper ground (breaker, fuse box or any pipes connecting to ground).

Actually, I checked the cables on the outside of my house and there's a little piece that's attached to the cable coupler on one end and the breaker box on the other end. WOuld a ground loop block be any different? The wires are all painted over but I figure this shouldn't affect the connections. Could it be that the ground wire or pole or whatever isn't buried deeply enough? Is there anything I should check or adjust on this connection?

 

[Lee-c]

If the cable ground is causing the problem, Mondial (I think it's Mondial) makes something they
call the "magic box" that gets rid of all hum caused by the cable in your stereo system.
You connect this little black box between your cable as it comes out of the wall and your VCR.
It cuts off the hum before it can even get into your VCR, and so it never makes it to your
stereo system. Problem solved. No wires to ground or anything, very neat and tidy solution.
As a bonus, I think Mondial says that the cable picture may even improve some after passing
through their box.
I think you can find one for maybe $50 or $60, if you check around. I plan to get one
myself, since my cable causes some hum, as well.

 

[Mike Veroukis]

Hiss is rather normal for receivers and many amps. A good high end amp will have much less (or no) hiss. You should only hear the hiss when you crank the volume. If the hiss is noticeable at low volume it could be your source. For example, if you just have your receiver on you will hear some hiss. You then set the input to CD player and turn your CD player on, you might hear some more hiss as the CD player will add some noise to the mix. Then when you hit play you might hear even more hiss, but that's probably just hiss in the recording.

As for your ground loop, is it very noticeable at all volumes? If you can hear the hum only at very high volumes then I wouldn't worry too much about it. On my setup the hum (before the fix) was loud at all volumes. After I installed the ground loop block still get a hum but it's very faint and I have to really crank the volume to hear it. In other words, its un-noticable under normal conditions and so it doesn't bother me.

The strange thing about my ground loop hum was that it hummed ONLY when I set the receiver's input to a source that carried the hum. What I mean is, my VCR was one source of hum, but I only heard the hum when I set the receiver to VCR. When I set it to CD player the hum was completely gone. It must have something to do with how the receiver switches inputs as others describe a hum regardless of input.

Marvin, Check to make sure that the connections are clean and secure. Sometimes badly crimped ends on the cable can introduce unwanted noise. Not sure what else to suggest at this point.

- Mike

 

[Vlad D]

What I mean is, my VCR was one source of hum, but I only heard the hum when I set the receiver to VCR. When I set it to CD player the hum was completely gone.

In my case it didn't matter what my input was set to. The VCR was the culprit, but I heard the hum even with the receiver set to DVD. I could hear it about a foot away from the speaker, unlike my hiss. It also disappeared when music was playing, or at least I couldn't hear it over the music. It was not volume dependent. Anyway, the VCR is no longer connected to my receiver - problem solved.

Just want to say thanks to everyone who helped my diagnose and fix the problem.

Now to fix the hiss, if possible.

 

[Marvin]

Would a line conditioner have any effect on hiss? I read somewhere that it may be due to other appliances, e.g. lamps, that are plugged in along the same circuit as the amp, somehow "polluting" the current. (I have no idea.)

 

[Marvin]

Just wondering if anyone has or knows anything about this item (first item on the page):
http://www.elect-spec.com/video.htm
This is more reasonably priced than the Mondial gadget that someone mentioned and I'm hoping it provides an alternative to using a cheater or disconnecting my cable/VCR, assuming I can't get rid of the hum any other way when I set up my amp.

 

[Bruce Chang]

I had the same problem and I figured it out. My sherbourn was making a bunch of noise and it was my AH! cd player causing the problem. I broke off the ground plug(used and aftermarket power cable) and all the hum went away. If you have any ground on the cables, just break it off.