VO-BB - 20 YEARS OLD!

[Raymond Hearn]

Hello all,
I posted awhile back about the fact that I was getting a buzz and RFI (local AM sports talk radio) in my audio input. Well I finally tracked down the source of the problem. Now what? First here's my studio set up

- Mbox plugged directly in to Mac Mini (also tried on a Macbook)
- Pro Tools LE 7
- Audio Technica AT4033a mic plugged directly into the Mbox
- Mic cable: 20' Prolink Standard 100 High Clarity Ultra Flexible cable by Monster Cable
- The most expensive heavily shielded USB cable Monster Cable makes
- 5 x 7 Whisper Room iso booth with 80% of the OC703 bass traps and absorption panels I plan to install (I still need to install a cloud.)
- Power cords are routed a good distance from all audio cables
- Furman classic series power conditioner.

Here's what I know: the root cause of the problem seems to be the AC coursing through my house, or maybe the power supplies in both of my computers are acting like an antenna. The buzz and RFI disappear when I let my Macbook run on battery. When I plug the Macbook into the power outlet the buzz and RFI come right back. I've tried several different power conditioners and none have helped. I tried a ground lift adapter and that didn't do the trick. I talked to a Furman tech and he didn't think any of their products would solve my problem. I moved my entire rig upstairs to test a different electrical circuit and the audio quality improved significantly, but still too noisy. A couple people have told me I should replace my Mbox 1 with a Firewire interface that comes with it's own power supply. The theory is that the noise in my AC is bleeding into the audio because both the power and audio signal are being conducted through the same (USB) cable. So the problem would be solved with an interface that gets its power from the wall and only uses the Firewire cable for audio (i.e. Mbox Pro). But I hate to go out and drop $500 or so on a theory. Any thoughts?
Regards,
Raymond
http://raymondhearn.com

[CurtZHP]

There are no actual audio signals traveling along a USB cable. It's strictly data at that point -- ones and zeros. RFI and EMI would not manifest themselves as hum and noise, but rather as data errors (which today's faster machines can easily cope with for the most part).

You said nothing about the mic cable. Have you tried a different one? The mic to preamp connection is one of the most vulnerable, because the signal voltage is so ridiculously low (measured in millivolts). If the cable is poor or the preamp is poorly designed, the cable can essentially act as a radio antenna.

Poor grounding in the home's electrical system will certainly aggravate such issues. A ground lift adapter is a band-aid at best, and a lousy one at that.

There is likely a flaw in your home's electrical grounding, something that should be addressed if only for safety reasons.

[Raymond Hearn]

I'm using a 20' Prolink Standard 100 High Clarity Ultra Flexible microphone cable by Monster Cable. My thought was that the cable was ruled out as the problem source because the noise/RFI comes and goes depending on whether the Macbook is plugged into the power outlet. Seems like the noise would be more or less constant if the mic cable was the problem?

So it sounds like I should have an electrician come in and confirm that my circuits are properly grounded to the Earth eh? I can see a ground wire coming out of the breaker box (in the basement) and it's connected to the water supply pipe that comes in from the outdoors. But I have no idea how things are wired inside the breaker box.
Raymond

[Mike Sommer]

Well it could be a combination of things do to the fact that it's happening on (if I'm reading correctly) two different computers.

First the Microphone cable. Just because it's Monster Cable does not mean it's good, as a matter of fact this brand is no better than any other consumer cable. Also standard "two wire + shield" XLR cable is susceptible to RF and electro magnetic interference. But there is a solution, Quad 4 Cable.

Quad 4 cable has two twisted pairs of "hot" and "cold" wires and a breaded shield. By twisting two wires going to the same lead, you've created a capacitor, thusly rejecting incoming or outgoing electro magnetic interference. I use Canare L-4E6S mic cable for almost all my gear, particularly for long runs- along with Neutrik connectors. Basically I roll my own cables. But you can get pre-made quad cables at a price.

Canare L-4E6S XLR Cable


Next, because the noise is eliminated when you use your laptops battery, it could be indicative of a ground loop, or a poor ground connection.

One day at a studio where I worked, had a really bad hum in the gear. It was in every line, and we tore the place apart looking for it. We went out to the breaker box and checked everything. Now, it just so happened that I knew the that Burbank had very sandy soil; it had also been a very dry year, and I noticed that the grounding rod was going through the asphalt paving. On a hunch I started breaking up the asphalt around the grounding rod, got the hose and started watering the grounding rod. Almost instantly, the hum went away.

Sometimes the ground is connected to the plumbing. This is not only dangerous, but it's not a very good ground. This should be checked. Also in some older homes there is no ground and often retrofit ground plugs are used, which rely on the conduit to supply ground. This is not a reliable means of grounding a circuit.

Also see what other appliances are connected to the circuit. These too can bring in RF into the line; it's very possible that one circuit is affecting another. Try shutting off all the breakers except the one that your equipment is connected too. Note if there is any hum. If not turn the breakers on one at a time until the hum comes back.. This could help you track down the source.



A quick test you can do is get one of these: http://www.homedepot.com/h_d1/N-5yc1vZ1xh7/R-100062242/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053 and test the grounding in your house.
Even if the house is properly grounded, it is not uncommon for there to be a ground loop somewhere along the line that you are using. This would be where the ground wire from one circuit is connected to a ground of another circuit- this would crated a ground loop. This is why I try to use isolated lines for the sound system, and computers. By using the battery you're breaking the ground loop between the computer and the M Box. Which in tern is creating an antenna also.

A ground lift is only applicable to your XLR or balanced connections between gear. This is rarely the case with modern equipment, but is common where vintage equipment is often thrown into the audio chain.
_________________
The Blog:
http://voiceoveraudio.blogspot.com/

Acoustics are counter-intuitive. If one thing is certain about acoustics, it is that if anything seems obvious it is probably wrong.

[CurtZHP]

Actually, the plumbing ground is required by code. It needs to be connected no further than 5 feet from where the pipe enters the house, it must be jumpered across the water meter, and it must be connected directly to the main panel. But then the code also requires an additional ground rod (some areas require two) in the earth outside the house.

[Mike Sommer]

The grounding to the plumbing is incase your holding onto the toaster and washing dishes at the same time. But the grounding rod is the only true means of grounding to earth, and if two are required they must be implemented with care- they must be connected to the ground buss. Danger! Will Robinson!! Danger!---NEVER, EVER, EVER RUN A STAND ALONE GROUND WIRE FOR YOUR HOMES ELECTRICAL TO A GROUNDING ROD, AND BYPASSING THE BOX.

What is your location so I can check your city's code.
_________________
The Blog:
http://voiceoveraudio.blogspot.com/

Acoustics are counter-intuitive. If one thing is certain about acoustics, it is that if anything seems obvious it is probably wrong.

[CurtZHP]

Wait a second. You mean I'm supposed to UNPLUG the toaster while I'm washing it?? That's what I've been doing wrong!!

[Raymond Hearn]

From what I can see, the electrical panel's only ground is the water supply pipe. It's connected to the pipe shortly after it enters the house and there is a jumper across the water meter. I live in Silver Spring, MD.

I'll try the progressive circuit testing approach you described as soon as possible.

BTW, what's the difference between a water pipe and a ground rod in terms of Earth ground? I thought grounding rods basically were pipes buried in the ground.

Thank you,
Raymond

[Deirdre]

Have you tried "lifting" the power to the computer?
That's when you use a 3-to-2 prong "adapter".


I have a number of things in my audio chain lifted to combat USB feedback.

If you are using a safe power source, you should be fine.
I've got a rack power strip, a Monster Power "power bar". I lift a few things off of that.
_________________
DBCooperVO.com
IMDB

[CurtZHP]

Ground rods are basically steel rods, 5/8" in diameter and 8 feet long, clad in copper. They are pounded into the ground usually at least 6 feet apart and connected to the ground buss on the panel with one continuous run of #6 copper wire. You're talking about $30-$40 dollars worth of materials. I know because I'm in the process of upgrading my whole system and had to add them.

Like Mike says, the pipe grounding is just a safety backup.

[Mike Sommer]

LET ME CLARIFY:
The purpose of the equipment bonding conductor ground is to provide a low impedance path between non-current-carrying metallic parts of equipment and one of the conductors of that electrical system's source so that should these parts become energized for any reason, such as a frayed or damaged conductor, a short circuit will occur and thus cause an overcurrent protection device such as a circuit breaker or fuse to activate and disconnect the faulted circuit. Note that the earth itself has no role in this fault-clearing process since current must return to its source, not the earth as is sometimes believed.

The ground to the pipe is merely a secondary direct source of ground that will lead back to the box. Appliances like toasters have two prong plugs and no ground. Thusly if an accidents occurs there is a means back to the main box to trip the circuit. And it is often the water in the pipe that becomes the conductor, because pipes are often replaced with plastic or have non conductive parts in the path. This is why there is a ground to the pipe.

Equipment "Earthing" conductor. This provides an electrical connection between non-current-carrying metallic parts of equipment and the earth. The reason for doing this is to limit the voltage imposed by lightning, line surges, and contact with higher voltage lines. Note: equipment earthing does not provide protection from equipment ground faults, unless it is a grounded system and the voltage is over one thousand volts. This is because the earth is generally a very poor conductor—it takes a large voltage to push enough current through it back to the electrical system's source to operate a circuit breaker or fuse.
EDIT: It is also to stabilize the voltage to earth during normal operation. In the past, water supply pipes were often used as ground electrodes, but this was banned in some countries when plastic pipe became popular.

Long-distance electromagnetic telegraph systems from 1820 onwards used two or more wires to carry the signal and return currents. It was discovered, that a ground could be used as the return path to complete the circuit, making the return wire unnecessary. However, there were problems with this system. During dry weather, it was discovered the ground connection often developed a high resistance, requiring water to be poured on the ground rod to enable the telegraph to work.

When telephony began to replace telegraphy, it was discovered that the currents in the earth induced by power systems, electrical interference, other telephone,circuits, and natural sources including lightning caused unacceptable interference to the audio signals, and the two-wire system was reintroduced.

Because high frequency signals can flow to earth through capacitance, capacitance to ground is an important factor in effectiveness of signal grounds. Thusly earth grounds can leak radio frequencies back into our gear.

This is why it can be so difficult to eliminate grounding interference- one thing tends to lead to another. This is where line voltage conditioners come into play.


You can also try plugging the preamp into one circuit and the computer into another and see if that helps.
_________________
The Blog:
http://voiceoveraudio.blogspot.com/

Acoustics are counter-intuitive. If one thing is certain about acoustics, it is that if anything seems obvious it is probably wrong.

[Mike Sommer]

You can also try unplugging the XLR connection from the Preamp to see if the interference stops. There may be an increase of hiss from the preamp (do to the absence of a load) but if it is your electrical grounding that's supplying the noise you should be able to hear it. If the interferance stops when you unplug the XLR, then you can either change the cable, and or add a ground lift to the preamp.
_________________
The Blog:
http://voiceoveraudio.blogspot.com/

Acoustics are counter-intuitive. If one thing is certain about acoustics, it is that if anything seems obvious it is probably wrong.

[Mike Sommer]

Some important information about your homes grounding.

It should be understood that your homes grounding is intended for Life Protection, not clean audio. Though most of us have very little problems with our systems, there is from time to time the occasional buzz that creeps in.

Grounding
For service entrance (where electrical service enters the building) code requires soil-resistivity of 25 ohms. Only about 10% of grounding polls meet this requirement - most fall in the 35 to 600 ohm range. Oddly enough most inspectors never check.

For clean audio, soil resistance requires 5 ohms.

A 5/8 copper clad rod is ok. But the copper cladding often comes off whilst it is being driven into the ground. The rod rusts, and loses its effectiveness in 10 years. "Nothing is forever."

Attaching ground to piping may seem ok , but the piping is not buried deep enough to give you proper grounding. The pipe maybe acting more as an antenna than anything.

If two grounding rods are needed, they need to be at least 20 feet apart so they do not interact with each other. This would go for grounds attache to pipes also.

If you have sandy soil or your soil has poor mineral content, you're going to have problems. One solution is using an ionic electrode (chemical) ground rod like the Lyncole XIT. It's a 2-inch diameter tube with weep holes drilled into it , and filled with rock-salt. To instal it you core a 6-inch diameter x 10-feet deep hole, set the tube in the center and fill the hole with a slurry of Bebtonite clay/soil conditioner. This forms a high conductivity / low corrosive bond to the the earth. In some cases you may need to go the extra mile and core down 20-feet. This is expensive but it's often what is needed to get rid of the hum.

Also hum is often be backtracked to an electricians error, of incorrectly installing the wiring of your home, by creating ground loops. This can be both dangerous and bad for the audiophile. A ground loop is in effect, a short in the grounding wire.

Most rooms have two lines coming into them, of varying length going back to the box, with all sorts of things connected to them in between, that crate buzz and hum. Track back a line to your box an make sure that there is nothing els on it. Make that your clean line- 20 amp is best. Here, with a good quality power strip/surge-protector you can connect your audio gear and your computer and you should not have a problem. Though it's not unheard of for an electrical device to send hum or buzz back through the box and into the house.

You can go even further by installing a 240-volt circuit line to your studio, and getting a rack mounted isolation transformer with splits to 20-amp breakers; creating your own isolated service.
_________________
The Blog:
http://voiceoveraudio.blogspot.com/

Acoustics are counter-intuitive. If one thing is certain about acoustics, it is that if anything seems obvious it is probably wrong.

[glenspot]

I had this same problem with my laptop. I blamed everything from the dell power supply, to the computer itself, to the audio card....

The experts have given their opinion, and are probably more "right" than I am.

But, my THEORY, is that our laptops are taking 110 household current and converting it to a much lower voltage. No matter how good the grounding in your house or studio is... the power supply is the source of the voltage going into your laptop. Most laptops I have seen are powered by a 2 line cord...meaning that the 3 prong 110 AC (positive, negative and ground) is converted to just positive and negative. So, no matter how clean or grounded your household current is (or isn't) it's the laptop power supply that is the final source of noise.

DB suggested using a 3 prong to 2 prong adapter, and i've found that THAT is exactly the solution that worked for me.

There may be "better" ways to fix it. But if a $.39 2 prong adapter will fix it.. then GREAT.

(Through the process trying to solve my problem, I also tried a Furhman power conditioner, a new USB audio interface, and standing on one foot while singing songs from My Fair Lady... the latter didn't help the situation, but it was my explanation to my wife when she caught me wearing a dress.)
_________________
Glen Pavlovich
www.glenpavlovich.com

[schrecster]

ok, the part he says about the MAC running on battery and not getting the buzz makes me say hmmmm. I know on my laptop, not a mac, there is a power converter. could that be bad and causing the buzz? Does the MAC use a power converter as well when not running on battery? I tried to read through other posts and see if you tried a different power supply but I didnt find anything.

If your mac uses a power converter I would see if you can borrow one from a friend and try that. if the buzz goes away, bad power supply...if the buzz persists, then you have not isolated the problem.

good luck, electrical problems can be a PITA to isolate the trouble on.