Hum FAQ - Page 3

I have humming or buzzing coming from all my speakers that is quite loud. It only occurs upon start up of the system and each time works its way out after maybe four minutes. I have been researching this and have not heard of a similar situation, so I was wondering if anyone here might have an idea of what is going on. I do not think it could be a ground loop issue as I have everything going through a power conditioner. I just find it odd that the loud buzzing suddenly works its way out after only a few minutes and is only every present during power up. Any help would be really great.

My system consists of: Various B&W speakers, Denon AVR 3300, Bryston 4BSST, SA8300HD, Toshiba HD-A1, etc.

I have a puzzling one also, at least to me. I read this thread with interest as I do have a noise issue. I would call it a hiss and not a buzz or hum. In any case, I ran through the process on page one; I disconnected everything from the receiver (NAD T773) except for the speakers. No change. So apparently it's not a ground loop, which I suspected from the nature of the sound.

Ok, so what to do. No easy solutions apparent. But then I started playing around and found something interesting. After hooking the DVD player backup (Denon 3910) I realized that if the receiver is on any digital source from the DVD, optical or coax, I have the hiss. If I use the 5.1 analog inputs as the source....the his is almost non existent.

Anyone ever seen this or is there an explanation? Any and all input appreciated.

I have a Sony 5.1 receiver with Sony sub. The humming noise occurs when I connect a 1/8th to stereo phono plug from my computer to any of the RCA inputs on my receiver. The other plug that needs to be connected is the digital coax from my HD-DVR Cable box (Motorola brand from Comcast). When both are connected to the receiver, the hum occurs. I have switched to Optical for the time being from my cable box, and the hum is gone. However I would like to know what I could do to stop this hum from occuring when the coax is connected as I would prefer to use coax.

If the optical works I would just use that, but if you want to use the coax audio connection, try one of the DC blockers, or ground breakers like the ones found towards the bottom of the linked page below. You can find them at Radio Shack as well. It will need to be placed on the cable just before it feeds the cable TV STB.

http://www.hometech.com/video/atten.html
RF Attenuators, Filters, & DC Blockers - HomeTech Solutions

Theoretically, if the cable feed is grounded properly you shouldn't have the problem, but it's an extremely common problem, and the above devices should fix it.

Greetings,

Could someone who Knows compare/contrast the Xantech ground blocker referenced in that link to the, rather more expensive, Jensen Transformers VRD-1FF (http://www.jensentransformers.com/iso_vid.html)?

Thanks.

(Don't know if these have already been mentioned in this thread...)

A friend of mine had a hum that seemed to be pervasive in his system. No matter what he did, no matter which component was the source his front speakers always hummed. It was driving him nuts for weeks.

When I went over, I saw he had about 20' of speaker wire coiled up and tied together laying on top of all the other wires in and out of his receiver. We cut down his speaker wire to minimum length required and that did the trick. Even though all of his cables were shielded, the current running through the coils of speaker wire was apparently creating an inductor (or whatever the AC equivalent is) and interfering with the currents in his other wires.

Another source of hum can be the room itself. I've heard listening rooms where the studs in the wall resonate, and the sheets of drywall on either side act as drum skins. This is usually only noticable at higher volumes.

Test

Interesting. Any chance have you had experiences with more of a "hiss" or a "crack/pop" from speakers? I auditioned a pre/pro recently and you could hear a hiss from about 4' away (my ref receiver was dead silent). Also, (perhaps not related), as I passed DirectTV through it, it would "crack/pop" every time I changed channels. I returned it to the owner and the problems went away.

Unfortunately for me, most of this thread is above my head, but I have what I think is an easy hum question...

7.1 setup, Denon 2807, 2 amps (for front & surround), Yamaha DVD. My hum obviously is associated with CATV, because when I unhook the cable for music listening, no more hum.

I believe there are enough plugs on my power conditioner (or whatever it's called) for everything, though I may have the sub plugged separately into same wall outlet. There are also CATV in/outs on the conditioner I recall (I'm not home at the moment).

Can I plug the CATV into the conditioner, and then from there into the TV? Will that do the trick, or am I way off base?

Thanks!

Some power conditioners have surge suppressors for cable (could be antenna, dish, or cable TV). But those do nothing to stop hum. Very few power conditioners include a cable surge suppressor that also "breaks" (interrupts) the ground/shield (the Furman 20i does have isolated ground AND surge suppression, other models of theirs may have the same feature, and other brands might have it too, but if they don't SAY it isolates the ground, it doesn't.

So let's assume you don't have one of the power conditioners that DOES isolate the cable ground... what should you do? There's a company called Jensen Transformers who makes an EXCELLENT quality ground loop breaker. You need a second piece of cable to use it. You plug 1 end of the existing cable into the isolator, then plug the new length of cable into the other end of the isolator and then to wherever you need it to be connected. Now the ground for the cable (the shield) is 'broken' and you have isolated the cable ground from the ground from the rest of your system.

Why does the system hum when you connect the cable now? The place the cable is grounded is different than the place your house wiring is grounded. The cable may be grounded to a bar driven into the ground somewhere outside of your house or possibly to a water pipe inside your house somewhere. If the cable installer had run a ground wire from the cable where it comes into your house to the ground rod for your home's entire electrical system, chances are, that would also stop your hum.

When grounds exist in 2 different physical locations, you end up with a real electrical current flowing between those 2 grounds and THAT current flow produces the hum you hear.

If you have Cable TV (not satellite) you want Jensen's Iso-Max VRD-1FF... $60 MSRP. It doesn't appear that they have a product that will work with a satellite feed which can have the same problem. In that case, trying to relocate the ground for the satellite feed to the home's electrical system ground could stop the problem too. Or perhaps some other company that makes these sort of devices has one that works with satellite systems.

When you have this sort of ground loop (different physical ground locations), you may notice that when the ground is wet, the hum is not quite as bad as when the ground is really dry! The moisture affects the conductivity of the earth/ground and that changes the amount of hum you hear in the system.

You probably CAN'T fix the hum by running a wire between 2 different ground rods. You have to physically disconnect from one ground rod (or water pipe) and ground everything to the home's ground rod (often a crow-bar looking thing sticking out of the basement or slab floor or out of the foundation somewhere, or beside the home somewhere not too far from the electrical panel (ours goes through the slab in the garage and the electrical panel is not far from the ground rod). Some fairly beefy wires will be clamped to that ground rod. You can clamp another wire to that rod (don't disturb the existing ground, get a new clamp and add it to the rod, Lowes and Home Depot have them in the electrical department) and run that wire to where the cable or satellite ground had been located before (sometimes to a splitter or a fitting in the cable with a ground screw and hole coming off one side with a bare wire held into the hole by the screw).

Ground loops are fun! Especially when you fix one!

I have a hum problem on my TV speaker audio. The audio source is the analog audio output from a STB via RCA cables. My HD STB has an digital audio output, but the TV doesn't have a digital audio input. Are there HD TV's that do have digital audio inputs?

Try using a DC-blocker on the cable feed to the STB like the one's listed in the linked page in post No. 64 above.

Anyone know of any Ground Breakers for use with Digital Cable? (all the ones I've found are not compatible with digital cable)

http://jensentransformers.com/

You want the VRD-1FF $59.95 - compatible with analog and digital cable.

Not compatible with satellite installations.

Thanks for the link!

I have a low hum that can only be heard with my ear up to the device. It is coming from a Onkyo 390 CD changer when it is off.

Is this normal or just floor noise from the player?

thanks...

I have a strange ground loop. I did what was recommended and disconnected everything from my prepro. The hum occurs when I put my Scientific Atlanta 4250HD cable box back in the circuit, but does not go away when I disconnect the cable input to the box. But if I disconnect the HDMI cable from the cable box to the prepro, or pull out the electrical cord from the cable box, the hum goes away. The hum is only heard when I use the Tv input on the prepro, not if I am watching a DVD or anything else. I tried bringing the cable box back to Cablevision, but a replacment cable box has the same problem. The box has a 2 prong plug, so I assume a ground lifting plug won't work.

I thought if the ground loop is coming from your cable, it would go away if you disconnect the cable feed from the cable box?

Any suggestions?

It's POSSIBLE the box would be quiet with a good ground from the cable - or not. Hard to know for sure.

Does your prepro have an AC convenience outlet on the back? If so, try plugging the cable box into that and see if the hum is still present. If it is not, you can either leave the box plugged in there, or you can plug the cable box into the same AC outlet as the prepro. Be sure when you connect the cable box to the prepro, the CABLE is not connected but do connect the HDMI cable to the monitor. You want to know if the box/monitor/prepro can be hum-free before introducing the cable. If you are hum-free without the CABLE and hum starts when you connect the cable, you'll need a cable isolator to break the ground loop.

Ground lifting plugs are dangerous and should be illegal - they can lead to electrocution if the product they are used with has a fault that allows AC to reach the chassis. Nobody should ever use a ground lifting plug unless you have a meter and can verify that the chassis is not floating at some potential that could electrocute you under the right conditions. But you said it was a 2-wire plug anyway - the ground is the 3rd wire so no-3rd wire, no ground is there to lift anyway. Products like that have to be manufactured a specific way to keep them from becoming an electrical shock hazard.

so I disconnected the cable wire from the cable box and turned it on, the hum is still there. But it goes away if I disconnect either the HDMI cable or the electrical plug from the cable box. There are no extra outlets on the back of my prepro, but I have it plugged into the same outlet. The HDMI cable is the better Blue Jeans cable, which should be pretty heavily shielded, so I don't think that's the issue. I tried plugging the HDMI cable into a different input on the back of the prepro, so I don't think it's a broken HDMI input on the prepro either.

1) Have I ruled out cable ground as being the source of the problem?
2) Any other suggestions?

Is the cable ruled out? Maybe, maybe not. It all depends on where else the cable goes. If it goes to a cable modem and you have an ethernet connection to a PC that's connected to the system somewhere - or an ethernet cable connected to a disc player that's connected to the pre-pro - the cable could still be implicated in a system hum problem. If the cable doesn't connect directly or indirectly to the system anywhere else, it sounds like you need an isolated HDMI interface - and I'm not sure if that's even possible, let alone available.

Try disconnecting all other components from the pre-pro and repeat your experiment with the cable box and hdmi cable to see if there's a hum issue without all the other components connected. If the hum is gone, you can connect other components 1-at-a-time to see if there's 1 component that brings the hum back. When you know what component that is, you can check where the connections come from and where that component is plugged in - moving the plug may help. Isolating the connections to the component may help.

I've read this thread and can't find the exact answer I'm looking for. I'll start with some set-up info and then explain my problem.

I'm using a Pioneer Vsx-80tx receiver. All of my speakers wires are routed through the walls and terminate at a speaker panel behind the receiver. I have a Klipsch RW-10d sub. The sub is digital, so I run pre-amp level signal wires (right and left) to the sub. This was set up and running for almost a year. Recently, I noticed a loud hum coming from the sub only. Here's the wierd part. When the receiver is on, I can't really hear anything, and when you turn it off, there is no hum. BUT, in about 90 seconds, the sub starts humming loud enough that I can hear it anywhere in the house. If I unplug the receiver (power cord) and plug it back in, the hum stops and then picks up in 90 seconds again. So, being an engineer, I assumed ground loop. I went through all the trouble shooting (unplug this and that) and determined that if I unplugg the phono plugs from the back of the sub, the hum stops. Plug them in and unplug the phono jacks from the receiver and the hum is literally deafening! So the problem is somewhere in the signal wires to the sub. I took a length of wire and attached it to the shield of the signal wires and then grounded it, and presto! Hum is gone. Even with everything plugged back together and the receiver turned off.

So my question is two parts. First, why did this suddenly start humming when the system is unchanged in anyway? Second, am I asking for trouble by grounding the signal shield to earth seperately from the internal grounding that should occur in the receiver or sub amp? I don't want to burn out my receiver.

I don't know why it would start now if it hadn't always been there. I have exactly the same issue in my system from time to time - configuration changes frequently though, so it comes and goes. But one AVR or another is always present when the problem happens and it's always the subwoofer connected to the LFE output on the receiver that hums. My sub has a ground post on the amplifier module. I connected a 16 gauge stranded copper wire from the ground post on the subwoofer to the ground post on the recever (normally would be used for a record player, you remember those? LPs? 45s? vinyl?) and that stopped 60% of my hum problem. The remainder of the hum problem was stopped by running a 10 gauge power-tool extension cord from the same power conditioner the receiver is plugged into all the way to the back of the room where the LFE subwoofer is located. That stopped the remaining 40% of the hum when the receiver was turned off.

Hope this helps!

PS - If you have no ground post on the subwoofer amp module, scrape some paint from around one of the mounting screws and put the ground wire under that mounting screw (assuming you have a metal plate on the back of the subwoofer).

I don't know what they heck they have done to these receivers to make the hum start like that when you turn off the receiver - it is really odd. Almost like they put a voltage on the shield/return of the line level outputs.

I have the problem with my cable tv not being properly grounded. When I disconnect the coax cable from the box, the hum goes away. I have digital cable, would one of those RF attenuators from Radioshack work just as well as one of those jensen transformers?

No, you have to isolate the ground - that's the whole point of an isolation device and it also accounts for why they are expensive compared to a simple attenuator that just reduces signal strength and nothing else. A resistor in a housing is all an attenuator is. An isolator has to have transformers that allow the signal to "jump" across from one side of the transformer to the other without having a physical connection.

Ok. Well how about those monster cable surge protectors? I know that they have hook ups for coax. Would one of those work? I ask, because I need a surge protector and that I way I don't have to pay for the transformer only and I'll get more use out of the surge protector.

Monster's coax connections don't isolate the ground on the cable connectors. They and everybody else I've checked so far don't go to the expense of isolating the cable ground... with 1 exception. Some Furman products with cable connections DO isolate the cable ground... the $3000 20i does, for example. Not sure how far down their product line you can go and still get the isolated cable ground though.

I have a ground loop issue between my computer and the receiver. Since the computer and receiver are on the same electrical circuit but different outlets, I end up with a group loop issue. The audio between the computer and receiver are connected via stranded copper wire with mini RCA 3.5mm and RCA jack ends. Though they both share the same ground wire, they're at different outlets which according to this thread creates two different ground potentials and therefore a ground loop. So I'm wondering, how can I alleviate this issue? This problem is different from the cable since all you have to do is use the same ground as the house wiring. Also how come my reciever doesn't have a 3 prog electrical plug? How exactly is it grounded?

Also btw, I was wondering if this was normal but when I turn up the volume to the max, along with the hum, I can actually hear the audio from another input that isn't selected.

You're problem would most likely be fixable with a stereo audio isolator inserted between the computer and receiver so there is no direct electrical connection between the receiver and computer -- the audio signal gets through across an isolation transformer.

However, if the computer is generating audio hum rather than an actual ground loop hum... that won't be stopped since that would be part of the signal. If you connect GOOD headphones to the computer... headphones that can produce actual bass frequencies below 50Hz, and you hear hum in the headphones, the computer is creating that and it's not a ground loop. If there's no hum in the headphones, you probably do have a ground loop. Do the headphone test with the computer disconnected from the receiver.

www.jensentransformers.com sells an excellent quality stereo audio isolator. There may be other sources with lower prices and lower audio quality. the quality of the transformers in these isolators has a pretty significant effect on audio quality. It won't bother compressed MP3 much, but if you are trying to play uncompressed sources and want good sound, the Jensen product is the way to go.

I'm getting a strange hum issue: my Kef 5005 (old model) powered sub hums only when my AV receiver (Onkyo 705) is off. When I turn the Onkyo on the hum goes away. Any pointers or is this a hum issue I shouldn't be worried about?

Something odd happens in many AVRs or processors with 2-wire power cords. I have the same thing happen with Onkyo and Pioneer AVRs of recent vintage and I suspect other brands are doing the same thing, whatever it is. If your sub has an external ground post, you can try running an extra ground wire from the sub to the AVR chassis, but that's not likely to solve the problem - those ground wires tend to be more effective when the AVR is powered-up.

If the AVR and sub aren't connected to the same power outlet or power conditioner, you could try an extension cord on the sub to see if it stops humming when plugged in to the same place the AVR is plugged in. But I wouldn't run out and get a big fancy extension cord right away, because this may not help either, try it with any old cord you have around the house first to see if that does any good. It should be a 3-wire cord if your sub has a 3-prong AC plug.