New amp, annoying buzz, need elec help (1 Viewer)

[Eric_Singer]

Hi,

I recently replaced my H/K AVR70 with separates - an H/K PA5800 with a PT2500 preamp. It works fine, but there is an audible background buzz that comes through the speakers now. It comes through each speaker equally loud, and changing the volume level of the preamp does not change the volume of the buzz. This, combined with the fact that there was no buzz before, leads me to believe that there is a problem with the amp's electrical connection. The amp uses a 2-prong plug with no ground, so I presume it would be safe to flip it around, but it only fits in the outlet one way. Would it be ok to use a cheater plug to flip it around, and would this likely solve the problem? Is there anything I am missing here? Any other possible sources of the buzz, or any other possible ways to fix it?

Thanks for your help,

Eric

 

[Han]

I could be wrong, but I always thought people who had three pronged plugs from their amps went the way of a cheater to get rid of humming. Not the other way around.

Try this:
unplug the pre-amp connections from the amp, and turn everything off except the amp. If there's no buzzing or whatever, try turning on various devices (TV, DVD player, Preamp) to see if it has something to do with too many things in that circuit. Still no buzzing, then plug the pre-amp outs back into the amp.

I'm plagued by a faint humming too, and have pretty much chalked it up to the electricity, since this wasn't a problem before I moved to my current house. Plus, only having the amp on still produces the humming.

 

[mike_decock]

I had a really bud buzzing sound when I dropped in a pair of tube monoblocks. Two hours of troubleshooting later I found out it was the TV Cable polluting the entire ground loop. Go figure!

-Mike...

 

[Marvin]

Eric,
You might also want to check out this thread if you haven't already:
http://www.hometheaterforum.com/htfo...threadid=72559

 

[Mike Veroukis]

Eric,

The link provided by Marvin should contain a lot of useful info in tracking down and eliminating the "buzz" or hum.

This is a very common problem and I have suffered from it too. To summarize quickly, the most common source of hum is what we call the ground loop problem. If you do a search for "ground loop" on these forums you'll find a lot of threads on this. The easiest way to diagnose this is to simply disconnect your cable TV cable at the point where it enters the house. If you have a sat. system you can disconnect this as well. If this makes the hum go away then the quickest and cheapest way to solve it is to go to RadioShack and buy a ground loop block. You will "splice" this adapter into the cable where it enters the house. You will then connect a cable (any cable will do, eg 12 ga speaker wire) from the block itself to a secure ground in your home (fuse box, pipes, etc). The hum should be gone or severely reduced. If you're uncomfortable doing this yourself the cable company should do it for you (free of charge if you're lucky).

Why this works; Basically, the ground potential of your home and the cable company does not match perfectly. Therefore there may be a small amount of current between your house and the cable company. This causes the hum. Since your receiver is grounded (or one of your components hooked up to it might be grounded) a current will flow from the cable company through the cable tv cable and through one of your A/V units. This will cause a hum. A cheater plug works by eliminating the ground prong and thus blocking any current that could result, thus no hum. Placing the ground loop block at the point of entry into your home will ground the cable tv cable and the ground potential will be equalized. Anything in your home now should be hum free if the source of the hum was the cable TV cable.

Btw, if your amp does not have a ground plug then you can assume it's not the cause. It's probably getting the hum from the pre-amp. I'm gonna venture a guess and say your pre-amp has a ground prong. It gets the hum from being physically connected to something like a TV or VCR or even a computer if you're using a cable modem. Disconnecting all of those from your pre-amp should also eliminate the hum.

Make sense?

- Mike

 

[Eric_Singer]

All,

Thanks for the tips. I will certainly try disconnecting my cable when I get back home. However, could this be the problem even though there was no buzz with my old receiver? My preamp doesn't have a ground plug either, actually. I figured that since changing the volume on it doesn't change the volume of the buzz, it must be in the amp, but I guess this isn't necessarily the case. I was considering the cheater plug because I've read that reversing a 2-prong plug in the socket sometimes helps and the current plug only fits in one way. It looks like I'll have to do a better job of narrowing the source down tonight.

Eric

 

[Mike Veroukis]

Eric,

Yeah, tracking down the ground loop can be confusing. It's never an obvious solution. I first noticed my hum when I hooked up my computer to my receiver. Funny thing is I got my receiver and cable modem at the same time, so it never occured to me it could be the cable modem. So I replaced cables, adapters you name it... I even thought the sound card was fried. I was ready to return my receiver! Then I found a thread on a forum about a hum and after reading more about it I realized it might not be any defective equipment. I disconnected the cable at the point of entry into the house and all the hum was gone. I still couldn't figure out why my computer would hum. It made sense for the VCR. And then it occured to me that the cable modem that was connected to my computer via standard network cable was the problem. So it seems to me that even a digital connection can cause a hum. Which makes me wonder what else can cause a hum... Perhaps a computer connected to a phone line via modem? Who knows, but you really have to disconnect everything and reconnect back one at a time and test it out. The results can often surprise you. Good luck!

- Mike

 

[mike_decock]

could this be the problem even though there was no buzz with my old receiver?

Yup, don't know why, but there was nothing wrong with my monoblocks. The problem just surfaced when I added them to the system.

-Mike...

 

[Greg_R]

could this be the problem even though there was no buzz with my old receiver?

Yes, certain components are more sensitive to noise. If the humming sound is coming from your amp (not your speakers) then it could be a loose transformer or other electrical issue inside the amplifier.

 

[Mike Veroukis]

Eric,

I should also point out that noise can be introduced through the electrical circuit as well. For example, halogen lamps or dimmers can cause unpredictable results when they are plugged into a cicruit along with your A/V gear. Just another thing to consider.

- Mike

 

[mike_decock]

I did notice in my troubleshooting efforts that running the TV cable through my Panamax 4300 resulted in about a 90% reduction in the buzzing sound. I think that power filtration/condition is a good investment to clean up the power/ground and give yourself a little piece of mind.

-Mike...

 

[Eric_Singer]

All,

Ok, I found the source of the buzz, but I'm now more confused than ever! When I unplugged the subwoofer interconnect cable from my preamp, the buzzing stopped. At first this made some sense to me, because the sub does have a grounded power cord, and since it is on the other side of the room, it appears to be on a different circuit. I then plugged the interconnect back into the preamp and unplugged the sub from the power outlet. The buzz remained. To make sure it wasn't the sub cable itself, I left it plugged into the preamp and unplugged the other end from the sub. Buzzing stopped. So the sub seems to be generating the buzz even when it is not receiving power. What gives? How is the buzz being generated from the sub, and how do I possibly get rid of it?

Thanks for your help,

Eric

 

[Mike Veroukis]

Hmmm... Yeah, that's confusing. I've never heard of that before. Perhaps you don't have a ground loop hum at all.
I wouldn't rule out the sub cable just yet though. If you unhooked the sub from the sub cable that would leave an open circuit and no current would flow. In other words the cable hasn't really been tested. You'd need to hook it up to something like a different sub or speaker to close the circuit. I think it needs some load so don't just short it (unless someone more knowledgeable the I says otherwise). Of course an easier way to check the cable is to simply use a different cable and hook it up to your components.
If it's not the cable then you should try a different sub. If it's not the sub try a different receiver or pre-amp. If that doesn't work try kicking it (just kidding).
Oh btw, does the sub buz at all? If so, under what conditions?
- Mike

 

[Eric_Singer]

The thing is that the sub never buzzes and the same sub and the same cable didn't cause any buzz when hooked up to my old receiver. I am just completely confused here. I will try to use a different interconnect to hook it up, though.

Eric

 

[Andrew_Ballew]

The ONLY component in my theater that has a 3 prong cord is the Monster HTPS 7000 Power Center. EVERYTHING else is two prong- my Carver amp, Rotel pre-amp, both powered subs, dvd player, etc. etc. My cable is grounded properly as well, so it is not the source.

I still have a slight hum or buzz from my speakers, even with everything off but the amp. So, I can only assume my hum comes from its internals, or the hum is introduced after the amplification stage in the speaker wiring. The hum still exists even when I unplug all input wiring to the amp.

Would everyone agree with my assessment? If so great- thank goodness the hum is so slight only the most critical of listeners would even notice it. Ignorance really IS bliss.


Cheers

Andrew B.

 

[Mike Veroukis]

Andrew,
I've read that other applicances or even light dimmers on the same circuit as your a/v gear can cause a hum. If the hum exists when your pre-pro/amp isn't connected to anything I would consider checking out what else is on that circuit. I would even consider plugging your gear straight into the wall socket by-passing the Monster power center.
When tracking down a hum the strategy is to simply strip things down to their most basic form to eliminate the hum. Once that is done you start adding things back one at a time until you get the hum, thus identifying the source.
Of course, in your case it could be that there's simply something wrong with your receiver. I would only conclude this once all other tests have been exhausted. Is this a new pre-pro/amp? Perhaps it's time to dig up it's warranty?
- Mike