Hum problem

I have a hum problem with my home theatre system.

I have a Carver TFM-55X for my front left and right speaker systems, a Carver TFM-35X in mono mode for my subwoofer and a Carver AV-705X 5-channel for the 4 surround speakers and the center channel speaker. I use a B&K Reference 30 surround processor/preamp.

I use a Directv H20 satellite receiver and a Mitsubishi WD-57734 television.

The Carver AV-705X and the Mitsubishi TV do not have 3-wire grounded AC cords. The Carver TFM-55X, TFM-35X, the B&K and the Directv receiver DO have 3-wire grounded AC cords.

I am assuming the hum problem, which manifests itself in the center channel speaker system when I have the B&K in the surround mode, is an AC ground loop hum problem.

Would there be any danger in connecting the chasses of the ungrounded components to ground?

I have a hum problem with my home theatre system.

I have a Carver TFM-55X for my front left and right speaker systems, a Carver TFM-35X in mono mode for my subwoofer and a Carver AV-705X 5-channel for the 4 surround speakers and the center channel speaker. I use a B&K Reference 30 surround processor/preamp.

I use a Directv H20 satellite receiver and a Mitsubishi WD-57734 television.

The Carver AV-705X and the Mitsubishi TV do not have 3-wire grounded AC cords. The Carver TFM-55X, TFM-35X, the B&K and the Directv receiver DO have 3-wire grounded AC cords.

I am assuming the hum problem, which manifests itself in the center channel speaker system when I have the B&K in the surround mode, is an AC ground loop hum problem.

Would there be any danger in connecting the chasses of the ungrounded components to ground?

Lets start by assuming that you have separate electrical circuits involved with all the equipment. Are you sure that they are all properly connected, true 3 wire circuits or, if you have an older home, were some of the original circuits "converted" to 3 wire along the way? You can easily check thsi out by getting a ground fault electrical tester at your local hardware store (looks like a large 3 wire electrical plug with 3 colored LEDs on it) and testing each circuit for proper ground before calling in an electrician.

Second thing to check, before even attempting to attach a ground wire to all the chassis, use a simple electrical tester to make sure that each chassis is a proper ground to a known good ground, that each chassis shows zero resistance to each other and that there is no voltatge differential between each chassis.

Third thing to check is that those pieces of equipment have polarized plugs on them. May sound stupid, but a non polarized plug can be inserted in either direction into both a polarized or non-polarized wall outlet. If you have a non-polarized plug on the AV-705X (not supposed to, but you never know) or if the electrical circuit it is plugged into is wrongly wired, then simply reversing the way the plug goes into the wall could resolve your hum problem. If reversing the plug corrects your problem, call in an electrician to correct the problem with the house wiring.

Next step would probably be to check out all the interconnect wiring to ensure that its integrity is good.

If after all this you still have the hum problem, then it may be time to call in the big guns on here; the guys who really know what they are talking about. they may recomment power conditionners, ground fault isolators or all sorts of other solutions, so doing the simple checks I outlined above are the easy, low cost steps that you would have to do before shelling out a lot of money anyways. Just be methodical and thorough in your testing.

Over the years I've found that I have been able to resolve every ground induced hum problem with these simple steps for litterally hundreds of clients (mostly back when I was in electronics sales). We all take for granted that just because there is a 3 pronged socket on the wall that it is hooked up right. You'd be surprised at how often newly added on electrical circuits can be out of phase with the existing electrical circuitry, especially when they were not installed by a certified electrician.

Hope this helps.

Thanks for the input.

I checked all the outlets in question with an outlet checker and all are wired properly.

All outlets are 3 wire outlets so there is no question that the components are plugged in correctly including the ones without 3-prong plugs. Those with 2 prong plugs all have polarized plugs with one prong wider than the other so they can't be plugged in improperly.

I checked the chasses of all components and all are grounded.

I didn't detect any voltage differences between any of the chasses although my meter's smallest range is 0-2.5V so there could possibly be a minute voltage present that the meter doesn't register.

I have seen advertised several "hum eliminators" priced between $20 and $60 that are to be placed in the audio circuit between components and one that goes between the outlet and the AC cord. Do you have any experience with these devices?

Thanks again for your response.

Thanks for the input.

I checked all the outlets in question with an outlet checker and all are wired properly.

All outlets are 3 wire outlets so there is no question that the components are plugged in correctly including the ones without 3-prong plugs. Those with 2 prong plugs all have polarized plugs with one prong wider than the other so they can't be plugged in improperly.

I checked the chasses of all components and all are grounded.

I didn't detect any voltage differences between any of the chasses although my meter's smallest range is 0-2.5V so there could possibly be a minute voltage present that the meter doesn't register.

I have seen advertised several "hum eliminators" priced between $20 and $60 that are to be placed in the audio circuit between components and one that goes between the outlet and the AC cord. Do you have any experience with these devices?

Thanks again for your response.

Just trying to get the obvious out of the way first before getting on to more involved solutions. Thing is most people "assume" that the electrical part of the equation just HAS to be right.

Now its time for the experts on here to bring their solutions to this problem. I know that there is a string somewhere on here that addresses specific devices that might help out. Do a search or hum or on ground isolators and see whaere that leads you.

Good luck and please keep us posted on your progress and eventual resolution.

I think I'd first try to connect the amp to the preamp and see what happens. Hum might go away or get louder. Have you tried changing channels on the 705 to see if the hum moves around to other speakers. If so, it might not be a ground loop problem at all - just an amp problem.

-mr billd; please don't say an amp problem[$$$+TIME] DRATTS

-i'm think'in a ground 'loop' problem or ic's[patchcord or connection]

-a 'tech', just mentioned a ground 'isolator' ??, of sorts in the 'audio' section..made sence to me

-all of the sugestions were good 'start tactics'

You check out the stuff that costs nothing or next to nothing first before throwing money at a problem like hum. Interconnects and the sequence in which equipment is plugged in are good follow-up steps I had forgotten to suggest. One bad interconnect ground is all it takes.

Problem solved!

It was indeed a ground loop AC hum problem and I tracked it down to the television set.

I disconnected all components from the preamp/processor and re-connected them one by one. When all audio inputs were disconnected, the hum problem disappeared. This eliminated any problem with the amplifiers. I then re-connected the components to the preamp/processor one by one to see where the hum came from. It was the TV set. Fortunately, the set has a digital optical audio output so there is no ground to the preamp/processor when it's connected to the preamp/processor's digital optical audio input. No ground, no ground loop. When connected to the preamp/processor using a digital optical cable, there was no hum.

The hum came back when I connected the VCR to the preamp/processor's input. This was because the VCR's video output was connected to the TV by standard RCA cables, again creating a ground loop hum problem since the audio output of the VCR was connected to the preamp/processor's input also by RCA cables. The VCR does not have an optical digital audio output (I'm not aware of any VCR that does) so I acquired a Behringer HD400 2-channel Hum Destroyer from Zzounds.com for $19.99 and connected the VCR's audio output through it to the preamp/processor. Hum gone.

Thanks to all for the input.

It would be simple if all components had balanced inputs and outputs but we don't live in that world. Next best is digital optical when available.

System consists of: B&K Reference 30 preamp/processor, Sony TC-K620 cassette deck, Toshiba SD-5205N CD/DVD changer, Carver C-1 preamp (using as a phono preamp only), Mitsubishi LT-22 turntable, Shure V15 Type IV cartridge, Carver TFM-35X in mono mode for subwoofer, Carver TFM-55X for left and right front speakers, Carver AV-705X for center channel and four surround speakers, Magnavox MVR650 VCR (playback only), Sony DVPNS77H DVD player, Directv H20 satellite receiver, Dynaudio Contour T2.5 left and right front speakers, Dayton 18" subwoofer, Sony SS-MB150H side surround speakers, JBL Control 1C rear surround speakers.

Great to see that you finally resolved your problem. Just goes to show that being systematic and thourough is the only way to eliminate weird problems.

That hum destroyer sounds like a great solution that we now have documented for anyone in the future.

Thanks for bringing us all a new solution for hum problems when you were the one asking for help.

Ain't forums great!!!

I found this in a Subwoofer User manual. Might be helpful for other hum problems.

If you have any electrical (50/60Hz) hum in your system you’re going to hear it clearly as soon as you hook up your subwoofer. Most hum problems are caused by “ground loops.â€

hmmmmm hm hm hm hmmmmmmmmmmmm

60 CYCLES/SECOND Check out EBTECH's HUM-X.

I've had both these situations occur in my rig--VCR causing hum and subwoofer causing ground loop. The VCR was an easy fix--I just took it out of my system...

I originally hooked up the sub between the preamp and the main amps with splitters on the RCA cables. The pre ran long RCA cables to the amps, and the ICs were connected to my monoblocks with splitters, and then a second set of long RCA cables went to the sub. It was 60Hz Hum City in the main speakers hooked up like this. I tried putting a "cheater plug" on the preamp. I tried plugging the subwoofer into a different outlet. I tried using a line conditioner on the subwoofer. Still major HUM. I finally ended up taking the sub off the main ICs, and plugging it into my surround processor. Not the ideal setup as far as integration with the main speakers when listening to 2-channel, but it got rid of the hum, which was, I guess not so much a ground loop through the power connectors, but a ground loop through the RCA connectors....

Glad to hear you got your problem resolved. Ground loop issues can drive you completely bonkers, and are usually resolved by a LOT of trial and error, cable switching, and a sprinkle of good luck...
--Richard

Isolation transformers (ie line level between subwoofer and amp) are pretty cheap if your problem is 60Hz hum. That is pretty easy to determine by trial-and-error. Switching out components until you've eliminated everything. But you've got stuff that isn't grounded to earth.
And, these inline devices filter and can possibly degrade the audio signal itself.

Just because most or even all of your components aren't earth grounded doesn't mean that loop noise is not the culprit! Look into this on the web and you will learn some important things.

Here's something to think about: if you test for voltage between the ground and either of the terminals of a standard household AC outlet, the meter should read zero, right? Try this and it may yield a little insight into how or why a circuit grounded to the earth has no 'potential difference' - it is "dead" - but that is not to say that it doesn't affect your power and thus your signal.


A company called Ebtech has answered a lot of people's prayers with their invention of a device called the Hum X. This device is plugged right into your 120V power outlet and effectively "floats" the earth ground of anything plugged in to it.

This is revolutionary! This thing is not in the audio signal path and does not affect your music by one iota. People spend jillions of dollars on power isolation transformers and even megawatt dedicated power sources
for huge, mobile PA systems. This thing eliminates some of the fortune people have to spend on things that interrupt signal paths and can compromise reproduction.

I can't testify personally to it's effectiveness but I have a strong feeling I am going to get one for my little home studio because things like guitars and amps generate insane 60-cycle hum.

They are only about $80 !

I did not read all the possible solutions, but do you have Dimmer switch anywhere in that end of the house ??
My Lightstar hums if I dim the lights in the livingroom...

For a budget sub-woofer audio isolation transformer see:
http://www.audioxpress.com/magsdirx/ax/ ... en2775.pdf