AAARRRGGGHHH! Please make the buzz stop!

[TLS Guy]

Well drats, I got the wrong kind of switch. The light is controlled from two different places and therefore needs a 3 way switch. But the bad news is - even with the dimmer switch completely out of the picture (circuit) I still have the buzz. This is getting really frustrating. I think next I’m going to have to physically separate power cords from inter-connects from speaker cable. One thing I did notice - with no power going to the pre-amp, and with just the amp on, the buzz is 99% gone.

That is making it sound like an old fashioned ground loop. Generally it is a bad idea and not necessary to use a ground to both an amp and a preamp.

I would ground the preamp only, and lift the ground to the amp. Do this first with just the preamp and amp connected and see if the buzz goes away.

Then load up the preamp inputs one by one, in case there is another ground loop set up by ancillary equipment.

The reason is that your balanced cables will ground the preamp and amp together soundly.

The the grounding plugs of the both the amp and preamp plugged in at the same time, just create the ground loop.

 

[CraigV]

Well, the news is not good. After replacing the dimmer switch, the buzz is still there. This morning I unhooked every connection into the preamp except for the connections between it & the amp, still have the buzz. I cut power to anything else I could think of that could be emitting radio frequencies - cordless phones, wi-fi router, laptops & even the Wii - still buzzing. I unplugged the pre from the Belkin power conditioner and plugged it into the same outlet as the amp, then unplugged the Belkin so the only devices anywhere near the pre & amp were the pre & amp, still have the buzz. I wanted to see the difference between the pre having power and not, so I pulled the power cord from the back of the pre and was treated to a very loud “burst” of high pitched energy going to the speakers. With no juice going to the pre, I got this big surge. Then, for a second, I had my thumb over the openings where the cord makes contact with the prongs on the preamp, and got the same loud squeal through the speakers. What the____? At this point, with the connection between the pre & amp but no juice going to the amp the buzz was gone. I then plugged the pre back in, and the buzz was back. This time I unplugged the pre from the wall socket - again a very loud squeal, and as I moved my fingers near the prongs of the cord & touched the outside of the plug (with no juice flowing into the pre) I got the same loud burst of a squeal.

I’m really loosing my mind with this one. I’m ready to bag the whole system & just listen through the TV speakers. I have my old Rotel RSP 1066 so I hooked it up. I first noticed a slight buzz from it, which prompted me to try the B&K. Now, I have removed the B&K and put the Rotel in it’s place. The original hum I heard is still there, but is MUCH quieter than the buzz from the B&K. Note - the Rotel uses unbalanced RCA cords, and the power cord does not have a ground prong (on either the preamp nor the power cord). I have to be pretty close to the speaker to hear this buzzy hum which I can hear in the tweeters, so I’m assuming it’s not the classic 60 cycle hum.

You have all been very gracious with your offers to help. Any more advice before I launch this stuff into the pond in my back yard?

 

[PENG]

think next I’m going to have to physically separate power cords from inter-connects from speaker cable.

That is a good idea, especially if you have long runs of interconnects between sources, preamp and amp.

One thing I did notice - with no power going to the pre-amp, and with just the amp on, the buzz is 99% gone.

You can easily eliminate the power amp being the culprit if you can hook up the B&K to another amp the same way. Can you borrow one from a friend? Did you notice this buzz from day 1?

 

[CraigV]

That is making it sound like an old fashioned ground loop. Generally it is a bad idea and not necessary to use a ground to both an amp and a preamp.

I would ground the preamp only, and lift the ground to the amp. Do this first with just the preamp and amp connected and see if the buzz goes away.

Then load up the preamp inputs one by one, in case there is another ground loop set up by ancillary equipment.

The reason is that your balanced cables will ground the preamp and amp together soundly.

The the grounding plugs of the both the amp and preamp plugged in at the same time, just create the ground loop.

But even when the preamp was plugged into the Belkin, which was plugged into a different outlet, the buzz was still there. The belkin has 8 outlets, and all 8 are taken up, some with 2 prong cords (sans grounds) and some with. If both outlets are on the same AC power line from the breaker box, would having a dedicated line for just the amp cure this? I plan on doing it anyway, but since the Rotel is offering me something I think I can live with, I might have to end my Ebay auction of it early (something I’ve never done and would hate to do since there are already bids on it & a lot of “watchers”)

 

[CraigV]

That is a good idea, especially if you have long runs of interconnects between sources, preamp and amp.



You can easily eliminate the power amp being the culprit if you can hook up the B&K to another amp the same way. Can you borrow one from a friend? Did you notice this buzz from day 1?

No

Oddly enough, no

And the interconnect runs are only 1 meter

 

[PENG]

Craig, I assume you had turned off the preamp before pulling the plug. Even then, if you touch any prong right after that you may still get the thump depending on the design of the preamp/amps due to the electrical charge still retained in the capacitors. I am still hoping you can try another power amp, even just a 2 channel one.

 

[CraigV]

Did you ever completely disconnect everything from the amp except the speakers, or did you just run it with the pre-amp unpowered? More of a curiousity, as your test appears to have proven out that it's not the amp.

The remaining buzz from the amp - does it sound like the hiss that's present with a lot of amps?

Yes, and it's barely there

 

[highfigh]

Craig- If you have a cable feed to the TV that doesn't come from the cable box (connects directly to the cable feed) and you have any cables connecting the TV to the rest of the equipment, you have a very common problem. Cable companies seldom ground the cable where it enters the building (this is required by the National Electrical Code) and they often are the source of this exact problem. If the noise went away when you disconnected the cable from the TV and you have a short coax cable that you're willing to sacrifice, remove the F connector from one end, strip the shield back so the center conductor is long enough to insert into the coax jack on the TV without the shield making contact, try that. If it removes the noise, buy an isolation adaptor for the cable feed. It works. Don't buy the cheapest one you can find, though.

 

[PENG]

Yes, and it's barely there

I am not sure if this has been asked already, does the buzzing noise level increases with volume? I mean if you turn the B&K volume up will the noise level increase accordingly?

 

[lsiberian]

craig aren't you driving very sensitive KEF speakers?

I think this may be an amp caused problem. I had an amp that did this and when I replaced it. The problem was fixed.

 

[CraigV]

Well here’s where I’m at. I just looked at the clock and I’m amazed it’s 4:00 PM. I’ve spent the better part of the day wiring up 2 new 20amp lines, one which has only the amp plugged into it, the other with only the B&K. I hook up the balanced interconnects, and the buzz returns. I then plug the preamp into the Belkin Power Conditioner, and it into the other dedicated line, and the buzz is still there. I remove the B&K, hook up the Rotel via RCA unbalanced & plugged into the Belkin - the buzz that was there before is still there, but quieter. Also, I did try the volume on both units, and only with the B&K does the noise get louder, while the Rotel stays the same. Right about now I’m ready to drink heavily and do something stupid, like buying a Sony receiver & Bose speakers.

While everything is still torn apart, I put the B&K back in and try the unbalanced RCA hookup. Hey, what do you know - no more buzz than the Rotel combination. This has me thinking about what TLS guy wrote:

That is making it sound like an old fashioned ground loop. Generally it is a bad idea and not necessary to use a ground to both an amp and a preamp.

I would ground the preamp only, and lift the ground to the amp. Do this first with just the preamp and amp connected and see if the buzz goes away.

Then load up the preamp inputs one by one, in case there is another ground loop set up by ancillary equipment.

The reason is that your balanced cables will ground the preamp and amp together soundly.

The the grounding plugs of the both the amp and preamp plugged in at the same time, just create the ground loop.

I’m not sure what “lifting the ground means” but when I switch back to the balanced interconnects, the buzz is there. With the unbalanced RCA’s, it’s gone.

 

[PENG]

Craig, thanks for sharing your experience in such great details and TLS guy deserves the credit, this time for sure. This thread will benefit many. The weekend is still young, time to enjoy your new twin 20A lines!

 

[highfigh]

Well here’s where I’m at. I just looked at the clock and I’m amazed it’s 4:00 PM. I’ve spent the better part of the day wiring up 2 new 20amp lines, one which has only the amp plugged into it, the other with only the B&K. I hook up the balanced interconnects, and the buzz returns. I then plug the preamp into the Belkin Power Conditioner, and it into the other dedicated line, and the buzz is still there. I remove the B&K, hook up the Rotel via RCA unbalanced & plugged into the Belkin - the buzz that was there before is still there, but quieter. Also, I did try the volume on both units, and only with the B&K does the noise get louder, while the Rotel stays the same. Right about now I’m ready to drink heavily and do something stupid, like buying a Sony receiver & Bose speakers.

While everything is still torn apart, I put the B&K back in and try the unbalanced RCA hookup. Hey, what do you know - no more buzz than the Rotel combination. This has me thinking about what TLS guy wrote:

I’m not sure what “lifting the ground means” but when I switch back to the balanced interconnects, the buzz is there. With the unbalanced RCA’s, it’s gone.

Anything connected to the system needs to be on the same circuit and phase. Look at the electrical service connection to your house- you should see three cables. One is neutral and the other two each carry 120V, but are out of phase with each other (think sine waves, with the peak of one where the valley of the other is. The difference between them, just like any other pair of sine waves that are out of phase, is the absolute value of the difference between each and zero. If one is at +120V and the other is -120V, their difference is 240V. If part of your system is on the + 120V leg and another part of the system is on the -120V leg and you lift the ground, you don't want to touch both at the same time under certain circumstances. If you want to know what a ground loop is, go to the home page and look for the AV University area.

You want the preamp and power amp to be plugged into the power management device. You also want the sources plugged into this. Your TV is probably far anough from the rest of the system that the neutral wire has enough resistance to cause a voltage drop. When this happens, the difference is made up wherever it can find a path, which usually ends up being on the audio and/or video cables. If your cable feed goes to the TV and not to a cable box, disconnect it, as I recommended before. If the noise goes away, do what I recommended. If not, make sure the neutral, hot and ground connections on EVERY receptacle are clean and tight, the hot and neutral haven't been reversed and the ground is intact from the end of the circuit to the breaker panel. Also, you need to make sure the grounding electrode is intact and up to code. This is connected to at least one ground stake and can be inside the building if it was retrofitted. Usually, it's outside and connected directly to the panel. If this isn't correctly done, you can have the problems you described.

On balanced cables, pin 1 is the ground, pin 2 is the normal audio connection (sometimes called "Hot) and pin 3 is the inverted audio connection (sometimes called "Cold). Lifting Pin 1 breaks the connection between the chassis of the pieces the cable is connected to and is a common way to remove noise from a system. The chassis of each piece in the system still needs to be grounded, for safety.

 

[CraigV]

The cable TV cable goes through the cable box & wasn’t even in play during the testing. One interesting note though - as I was putting everything back together, I accidentally pulled the amp power cable out from the back of the amp. When I went to put it back in I noticed only two prongs. Does this mean the amp has no ground?

 

[CraigV]

I was able to unsolder the ground wire on one of the balanced XLR cables - still got the buzz.

 

[PENG]

When I went to put it back in I noticed only two prongs. Does this mean the amp has no ground?

Not really, the neutral wire should not be confused with the ground wire but it is in fact grounded at the panel.

 

[highfigh]

craig aren't you driving very sensitive KEF speakers?

I think this may be an amp caused problem. I had an amp that did this and when I replaced it. The problem was fixed.

Wait- "very sensitive" KEF speakers? Is there such a thing? I thought most of theirs were pretty insensitive, like 86dB/W.

 

[highfigh]

The cable TV cable goes through the cable box & wasn’t even in play during the testing. One interesting note though - as I was putting everything back together, I accidentally pulled the amp power cable out from the back of the amp. When I went to put it back in I noticed only two prongs. Does this mean the amp has no ground?

Yup. Look at the amp's receptacle for the power cord- if that only has two prongs, it's not grounded.

How are your wires arranged behind the equipment? Are they all wrapped in tight coils and laying together or tied together? This would cause some problems, but it's hard to guess how much/ If the interconnects are run parallel to power wiring, that's a no-no, too.

 

[TLS Guy]

The cable TV cable goes through the cable box & wasn’t even in play during the testing. One interesting note though - as I was putting everything back together, I accidentally pulled the amp power cable out from the back of the amp. When I went to put it back in I noticed only two prongs. Does this mean the amp has no ground?

Yes, that does mean the amp is not grounded.

Interestingly I read a paper recently showing that with most domestic equipment with balanced inputs, the balanced connection actually increased noise, due to imperfect balance at the inputs.

As I understand it the Rotel and the B & K with unbalanced connection have minimal buzz. Is that correct?

You might want to check that the neutral connection in your panel is in good order.

 

[PENG]

Yes, that does mean the amp is not grounded.

The amp in this case is not grounded by the ground wire but it is important to know that the neutral wire is, and should be connected to ground at the main incoming panel.

When the neutral is not carrying currents, meaning nothing is turned on, it is at ground potential. As soon as the load (example: the amp) is turned on, the neutral wire will carry current and it will be at a slightly (depends on the load current but typically very low) higher potential than ground (0V).