Speaker Hum Revisited (Again!) (1 Viewer)

[Chris Ryan]

OK, I just rewired my home theater to clean up the wire monster back there.

It is a dedicated room with in-wall 14-4 ga. speaker wire and an in-wall equipment rack. However, I'm STILL having a problem with low-level hum whenever my amp is on. I tested it with nothing hooked up except Monster Interlink III's between my Denon 5800 & my Sunfire Cinema Grand. The front three speakers and the side surrounds are hooked up to the amp. The back surrounds (3) are hooked up to the Denon. Of course, I got hum through the speakers on the CG. All my components are on a seperate 20 amp circuit and are plugged into a Monster HTPS 7000. My TV (Pioneer Elite 610) and subs (Infinity Intermezzo 1.2s & Def Tech. BP2000 TL's) are on a seperate 20-amp circuit plugged into a Monster Power 3500. None of the sub amps were plugged in for the test. If you are thinking cable ground, I have a Dish Network setup.

The minute the amp turns itself off, the hum is gone. I have called Sunfire and they insist that there is no way it could be the amp. I do have a 2nd breaker box.

By the way, I never had hum when I had the system hooked up upstairs.

Any ideas? Do you think it the inwall speaker wire? I also have RG6 coax terminated with F to RCA connector inwall for component.

Chris

 

[Steve Zimmerman]

I agree. It's NOT the amp itself.

(1) Have you temporarily used a cheater plug to see if that causes the hum to go away? My guess is that it will.

(2) Do you have dimming lights? I had some three-way lamps that made my amp go hummmm. I also have an iScan Pro line doubler that appears to cause my amps to hum when it's in the signal path.

(3) Have you tried disconnecting *EVERYTHING* except the signal processor (i.e. receiver or preamp), the amp, and the speakers? In other words, no video, no CD, no DVD, no monster HTPS, no nothing.

--Steve

 

[brucek]

Chris,

If you are thinking cable ground, I have a Dish Network setup.

Satellite systems are just as likely as cable TV to cause a ground loop. The shield of the RG6 coax from the DSS system is introducing another ground potential into your system and can easily cause a ground loop. DSS systems are notoriously incorrectly grounded.

Try removing the RG6 wire into your DSS receiver and see if is the culprit...

brucek

 

[Chris Ryan]

Thanks for the replies!

The cinema grand does not use a grounded plug. I'm certain it's between my Denon and my amp at the interconnects because the hum was present with just the interconnects being plugged in (along with the speaker wire). What is the easiest way to fix that?

Thanks,
Chris

 

[brucek]

Chris,

So you're saying that the Sunfire and Denon are plugged into the same AC circuit, and the Denon has "absolutely" no sources hooked into it, and you only have the interconnects between the Denon and Sunfire connected....

If so, you likely have an open shield in one of your interconnects. This can be solved by disconnecting them all and then connecting them one by one to determine which one is faulty.
Not likely the Sunfire, although easily determined by hooking it up standalone with speakers only and no inputs.
Not likely your AC circuit, although easily solved by powering your amp with an extension cord to another circuit temporarily.
Not likely your preamp, although easily solved by running it standalone using its internal power amplifiers.

brucek

 

[Chris Ryan]

My rack components have a dedicated 20A circuit. 1 outlet inside the rack. The only thing plugged into the outlet is my Monster 7000. All others are of course plugged into the Monster (including my amp). If I plug the amp directly into the outlet, it still hums.

I disconnected the interconnects from the Denon going to the amp - no hum. But, when I touched the end of each disconnected cable (one at a time), the hum was back.

My rear surround speakers are powered by my Denon alone. No hum when playing a CD through them.

Unfortunately, I can't plug the amp into another circuit because the back of my rack is in my utility room and no other outlet is close.

So, what is the easiest way to ground the two units? A piece of copper between the Denon and the amp?

 

[brucek]

Chris,

when I touched the end of each disconnected cable (one at a time), the hum was back

I wonder if you could explain this statement further? Touched the end?

brucek

 

[Chris Ryan]

One end of each cable was still plugged into the amp, the other ends were unplugged from the Denon and hanging free. I touched each RCA end (the part that plugs in to the inputs, the gold tip of the cables) of the Monster interconnects, one at a time, and the hum was back with every one.

 

[brucek]

Chris,

Yes, that's normal. If you plug an interconnect into an amplifier and touch the free ends' tip, it will hum. You are a introducing a signal into the amplifier from your body - you make a nice antenna. This is not what I was indicating for you to do.

Here's what I wanted you to do:

Unplug all interconnect cables from the Sunfire amplifier. The amp should now be hum free....

Now connect one interconnect from the Denon to the amplifier (i.e LeftFront). The Denon should have no source interconnects (analog or digital) hooked to it for this test. With this single interconnect from the Denon to the Sunfire, does it hum from the LF speaker? If so, is it volume dependant? Does substituting another interconnect cable in place of this one cable exhibit the same hum?

brucek

 

[Chris Ryan]

Thanks Bruce! Yes, it hums from the LF speaker. No, it's not volume dependent. The hum occurs with a different interconnect as well.

 

[brucek]

Chris,
Well, if you have both the Sunfire amp and Denon preamp/receiver plugged into the same power (and not using the conditioner), and no sources (digital or analog) are hooked into the preamp/receiver, while using a single interconnect from the preamp/receiver to the amp - and it still hums (without volume control dependancy), but does not hum from the receivers built in power amps, then it would initially indicate you must have a small difference in potential between the preamp/receivers' case ground and the amps DC ground at its RCA plugs (since you've stated that it is a two prong device).
This would seem very strange because usually with two prong devices, the DC ground is basically not referenced to AC ground at the device. The DC ground is developed after the power transformer and rectifier and is considered floating with reference to AC ground. Sometimes they'll isolate the RCA connectors on a two prong device and leave the case disconnected for possible grounding with an external screw, or they'll couple the DC ground to case with a small resistor or simply bolt the RCA connectors directly to the case. Either way, there is no path to AC ground to produce a conventional ground loop and subsequent hum.
This would indicate a low frequency signal (hum) coming from the Denon on its line level signal, that is simply being amplified by the Sunfire. This also seems quite strange because you indicate that when using the Denons' own internal amplifiers, that there is no hum. It also seems strange, because a hum produced internally in the Denon or by a source would very likely be volume sensitive, since the volume controllers are at the end of the preamp chain.
As a temporary test it would be interesting to "cheat" the Denon (if it's a three prong device) and see if this cleared the problem.
I also wonder if the Sunfire's case is somewhere "contacting" the in wall equipment rack, which may be safety grounded. This would be providing an unwanted connection between the Denons case (at DC ground) to the safety grounds potential.
I also wonder how long your interconnects are between the Denon and Sunfire and whether they are crossing some noisy source.
Other than that I'm afraid with the information I have and the inability to "mess" with your system myself - you've stumped me.........
brucek

 

[ChrisB]

FWIW- I just got home from work and had a hum from my amp. I had never had one before and this was a wiered one. When the telephone rang it got worse. I checked everything in back, pluged the amp into the surge supressor, still a humm. I then went out side and took my screwdriver and tightned up my ground where my cable(TV) enters the house. Presto, fixed!!! I guess with the changing weather we are having here, the wire had contracted and expanded(wires do this) and made itself loose. I am not sure if you checked this yet, but it worked for me!

 

[Vlad D]

Chris,

Did you ever find the cause of the "hum?" And if so, how did you solve it? I ask because I have a Denon 2802 and recently connected it to a Parasound amp, and I also have a "hum." Same as in your case it is a low level "hum," not volume dependent, and was not there when I used the Denon's internal amps.

 

[RichardMA]

Believe it or not, your television can induce periodic
and varying levels of hum in speakers if it's in close
proximity or plugged into the same circuit as your
other equipment. I've even heard the hum change as the
picture changes.

 

[Doug_NHT]

What is your volume setting when you hear this hum??? Can you hear it when you have your volume set to say, -60db??? Do you hear the hum at all volume levels???

 

[Vlad D]

Yes, I hear at all volumes. The hum does not get louder or lower as I raise or lower the volume.

 

[Paul Clarke]

Vlad,

The same thing happened to me with my 510/855A setup. It did not happen with the 310/855A. I simply used a cheater plug and for the amp and now the hum is gone.

 

[Vlad D]

Thanks Paul. What's a "cheater plug?" :b

 

[Paul Clarke]

Hi Vlad,

Go to the hardware store, electrical supply, hell, even some grocery stores have 'em. They are usually grey in color and simply convert a three prong plug as on your 855A into a two prong. They work like a charm. And you can still ground it using a screw.

 

[Mike Veroukis]

Using a cheater plug for a permanent solution is risky business. The cheater plug is like a plug adapter. You plug your receiver in one end and then plug the cheater plug into the wall outlet. The catch is that the cheater plug does not have a ground prong. This means that your receiver (or whatever) is no longer grounded and if something weird happens internally and you touch the receiver at that time you can act as the ground and fry yourself. The risk is a calculated one as most people tend to use remotes more often these days anyways, but you should be aware of the dangers. The ground prong is there for a reason.
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