Recording Interference

[OmegaZero]

I am having trouble with interference while recording my guitars. I know there's already a similar post, however my issue is pretty specific and I didn't want to hijack bluetigerstudios' thread.

What I am getting is a broad-band interference signal centered around 2 kHz - see attached spectrum readout. It does not seem to be a radio station or anything like that; just a loud buzzing noise. Unfortunately 2k is right in the middle of a guitar's frequency range so I can’t use an EQ or noise reduction/gate to remove it without killing the music. All of my equipment is running on a Furman AR-15 II power conditioner, though I have also tried a Monster PRO 3500 and plugging it in directly. All cabling is Mogami & Monster balanced TRS or XLR with the exception of the guitar and mic connections. I have tried various different connections, equipment, instruments, and cable lengths with no luck. Testing with a battery powered guitar processor I was able to walk around the house and found that the noise became worse when I was close to the breaker panel. Assuming from this that it was power problem, I tried switching off all of the breakers in my place except the one running my gear - no luck. The only way I could get it to go away was by switching off the service disconnect in my breaker box (again testing with a battery powered unit). I've had two different electricians out to check the wiring and grounding - both said everything is in good shape.

I have been able to record with this same gear in two previous residences without having this problem and quite frankly I 'm baffled. At this point I am about ready to sell the place. Can anyone point me at what to try next? Or even who to call?

[OmegaZero]

I should also add that there are no fluorescent lights, CRT TVs/monitors, computers, or unshielded speakers in the room with the guitars being recorded.

[dkerr]

Generally speaking electricians know bugger all about ground loops or radio interference. Nor do they have any equipment to usually track such things.

It looks like you have done a good job in trying to trace it. If you know of a amateur radio group in the area, see if can find someone experienced there, these groups often have people that are good at finding things like ground loops, and interference, grounding issues. They may be willing to help you out at a reasonable price that can help you finally locate the problem and come up with real solutions.

Have you had the opportunity to test it using a ups as a power source, there are different types of ups, type that basically uses AC and switches in a micro second when there is a loss of home AC, the other type has your equipment always running on battery generated AC and the home AC only keeps the batteries charged. The type that always runs your requipment on battery generated AC is the best as it filters out most things but is more expensive to buy.

A UPS may help when the problem is orginating from the home AC system, but may not help if it radio wave type interference.

Although the electrician that did the checks should have notice this, but make sure the polarity of the electrical outlet is correct, in which part of the outlet has the grounded conductor (neutral), and ungrounded conductor (hot), and that the equipment grounding conductor is actually connected to the plug. The other thing is to replace the actual outlet in the wall with a new outlet. Outlets are very cheap, so you are only loosing a couple of dollars if it does not solve anything. There is testers that you can get that will tell you all that and they are quite cheap, just plug it in the wall and it will tell you thru some colored lights is everything is connected right at the outlet. If it should be an older house, with outlets that are quite a few years old, a bad outlet could generated interference, sometimes a breaker can do that, even though the breaker technically does the job, it still may cause inference. That is where sometimes a really experience highly technical amateur radio operator may be able to track it down.

[suemarkp]

If you turn just the circuit breaker to your power conditioner off, does the noise go away (again, you'll have to run on battery power)? If so, it sounds like there is crap on the line that is getting past your filter (narrows things do to being on the line, -vs- being induced into the system). Do you know what type of filtering is done in the Furman conditioner (are there inductors in series with the power input lines)?

You could try plugging the Furman unit into an isolation transformer. I'd also try to keep the output of that isolation transformer ungrounded to the earth (but bonded only to the transformer output). If that works, see if it still works with the secondary being grounded to one of the ground wires in your house, as that is safer.

A UPS may not help unless it is the double conversion type, as those continually rectify and invert whereas the cheap one only rectify when power has gone away. Or you could record only when the UPS is running on batteries, assuming a UPS isolates you from the noise. But cheap UPS's may have their own generated noise.

[Mr T]

a few random thoughts.

Most normal AC electrical noise hangs out at 60hz. Stepper motors and other sensitive speed controlled motors can run at about the 2k range depending on their speed. A tape recorder/player wouldnt use that fancy of motors (normally) but a CD player/recorder will. WHat are you using to record?

A DC to DC converter or some power inverters run at a higher internal frequency. A power conditioner typically will pulate a DC voltage to make a AC signal. Backlt LCD screens often run at high voltage and use a inverter setup too. Look at equipment that uses screens like this. (this doesnt include screens lit up by a light bulb).

You said you plugged all your equipment into a power conditioner and ran it all without. Have you tried connecting equipement 1 at a time to the conditioner and runnign the rest from the wall. If one of your pieces of equipment is feeding out this noise it will travel to anything thats on the same outlet bank of the conditioner if it has isolated outlet banks, otherwise it will go to anything thats connected to the conditioner. A conditioner will only isolate noise going all the way through it.

do you also get this noise out any speakers or just on the recording? Have you tried unplugging various signal cables between the guitar and your recorder to see if the noise is still present. The noise may or may not be travellign through signal cables.

keep us posted

[OmegaZero]

Thank you all for the info and suggestions!

The battery powered unit I used was a portable that runs on AAAs with my guitar & headphones plugged directly into it, so it was an isolated circuit. Unfortunately I still had the same interference, which leads me to believe the signal is being picked up out of the air by my guitar's pickups. Would a UPS help much with that?

Over the weekend I went through and removed everything (literally, everything) from the room, disconnected every plug in the house (including the washer, dryer, refrigerator, etc), switched off all of the lights, and cut all of the breakers except for the one used by my gear. I also pulled my pre-amp (digital, solid state) out of the rack and hooked it up all by itself, so it was literally the only thing in the house that was connected to power. I also tried 3 different guitar cables of varying lengths as well as two sets of headphones with different length cables. No change in the interference.

Based on what I'm hearing here and from a few other sources, I am really starting to think that this interference is coming in from the street. I'm thinking of having someone come out with a scope to check the feed into my breaker box before the master disconnect to see if it is present at that point. That should nail it down as coming from the power company, right? If so, what can I do then? Maybe a whole-house power conditioner? $$$ :(

[suemarkp]

You still need to determine whether this interference is coming in via your power branch circuit, or being radiated through the air. If you can find a power inverter that has a nice output and connect it to your car battery for a bit, that may give you a test set. If that inverter will run the preamp and power amp and guitar without noise, then you're getting closer. If it is still noisy, drive away from your house to an isolated spot (e.g. a park with no power lines) and see if you still get noise. Some inverters may be crap, so you want to get a decent way to make the system work without noise that is portable (may want to include your Furman power conditioner and plug that into the inverter output).

Once you have that, turn off your main breaker and repeat (OK to leave other things plugged in). If that is OK, turn on only the branch circuit to your sound equipment and try again (but don't connect your isolated guitar/amp/preamp to it yet). If things are still fine, then try powering the isolated system from this branch circuit instead of the inverter. If it gets noise now, then the noise is on the power line. If you didn't get this far, the interference is most likely is radiated and you'll have to shield your house or music room or move away or see if the power company can filter it.

If the power line is noisy, you need a better power conditioner. This could be any or all the following: isolation transformer, UPS, power line conditioner/filter with series filtering (not a surge suppressor). A series filter is the only way to get rid of serious noise, and these are basically coils of wire on an iron core. Because a series filer has to be rated for the amps you'll be using, a 15A branch circuit filter will be way cheaper than a whole house one that would have to filter 200A worth of current. A 15A rated one is a few hundred bucks or more and will filter out just about everything upstream of that branch circuit (i.e. outside direct powerline noise, and noise from other circuits in your home). A 200A one would be cost prohibitive for most people, and would not filter out interference sources from inside the house.

[Mr T]

One other thing you can try as a last ditch effort to isolate your signal as interference is to put a signal isolater in your audio path. You can find these at car stereo shops. They come with RCA jacks but you can probably mod it to fit a 1/4" or whatever farily easily. Try it at various points in your signal path. it will break any physical connection between your guitar and the preamp or any other device in your signal path. It more or less is a 1:1 transformer.

THey are about $20. Ive had to use these before when I connected my computer to my home stereo to play music.

Otherwise start walpapering your house in tinfoil.....:eviltongue:

[OmegaZero]

Thank you all for your help and info. I was able to get someone with a scope out to my place - we could see the interference clearly when taking a reading at the service disconnect breaker (before it enters the house), so I'm pretty certain the signal is coming in from the street. At this point I am looking into a whole-house power conditioner... hopefully it won't be a billion dollars.

Thanks again!