Radio station noise

[primalsteve]

I just built a studio and I'm having some issues with what I'm guessing is a local radio station coming into the signal of certain sources. As of right now the sources it bleeds into are a Manley Reference Cardioid mic that works fine at a friends house, certain guitar amps, and my console(Soundcraft TS12)

The noise in the console eventually went away when we shortened the extra channel ribbon attached to the console. It was the main ribbon used for bussing and power, etc.. There were an extra 12 channels on the ribbon. We cut them off and that fixed the problem.


Any ideas? The power is a 100 amp sub-panel off of the main 200amps service. There are two types of power that we use. One is just the standard and is run in a normal fashion. The other is isolated grounds. Each 20amp isolated ground outlet runs back to it's own lug on a separate ground bar that terminates at earth about 5' away. The problem happens on both types of outlets but is more pronounced on the standard general use outlets. On the Manley the interference is literally like tuning into a radio station it is so loud and clear. Various other tube mics like a few Korby mics do not have this issue.

Thoughts?


Steve

[Led]

Sound like with so many things picking it up it may be in your ac lines. Do you have power conditioners in line? If not maybe try a Furman or the like and see if it fixes it.

[guitarbill]

Hi, I've got some questions for you. The first is why are you running isolated grounds? This might be one of your problems. Seperating AC grounds in a studio setup sounds kinda strange. Running power from two different panels is also asking for trouble because of the small difference of potential that can exist. If you have not done so already I would urge you to contact a licensed electrician who hopefully knows something about powering up studios. Make sure your power all comes from the same panel at least and that the grounding rods for it really are good. If the grounding rods are old you should get the electrician to drive a couple of brand new ones to code just to make sure. One rod is not good enough and not to code!

If you get your power issues taken care of and you still have RFI, you may want to try some power filters made by Triplite or a UPS (most of them have built in RFI filters).

A couple of more questions if the power is not the source of your RFI: is it an AM or an FM station? Another useful piece of information would be which station is it and where is the transmitter's antenna? If it's transmitting antenna is close to you, you may be in for a long process of getting rid of your gear that is being swamped by the signal or modifying the gear with feedthrough caps, rf bypass caps, and Corcom or equivalent RFI filters for the ac input power (which is probably not your best option unless you just can't live without it).

In the mid seventies I worked as a repair tech at a music store that was about two blocks from an AM tower. Almost every piece of gear we had recieved it loud and clear. Back then we just lived with it and told our customers that the gear wouldn't be swamped when they got it home! As long as they didn't live near it!

BTW good job on getting it out of your console!

Good luck
gb

[primalsteve]

Originally Posted by guitarbill

Hi, I've got some questions for you. The first is why are you running isolated grounds? This might be one of your problems. Seperating AC grounds in a studio setup sounds kinda strange. Running power from two different panels is also asking for trouble because of the small difference of potential that can exist. If you have not done so already I would urge you to contact a licensed electrician who hopefully knows something about powering up studios. Make sure your power all comes from the same panel at least and that the grounding rods for it really are good. If the grounding rods are old you should get the electrician to drive a couple of brand new ones to code just to make sure. One rod is not good enough and not to code!

If you get your power issues taken care of and you still have RFI, you may want to try some power filters made by Triplite or a UPS (most of them have built in RFI filters).

A couple of more questions if the power is not the source of your RFI: is it an AM or an FM station? Another useful piece of information would be which station is it and where is the transmitter's antenna? If it's transmitting antenna is close to you, you may be in for a long process of getting rid of your gear that is being swamped by the signal or modifying the gear with feedthrough caps, rf bypass caps, and Corcom or equivalent RFI filters for the ac input power (which is probably not your best option unless you just can't live without it).

In the mid seventies I worked as a repair tech at a music store that was about two blocks from an AM tower. Almost every piece of gear we had recieved it loud and clear. Back then we just lived with it and told our customers that the gear wouldn't be swamped when they got it home! As long as they didn't live near it!

BTW good job on getting it out of your console!

Good luck
gb

Thanks for the feedback. To clear up a few things here's the setup.


The main 200amp panel is the main panel for the home. The studio(seperate building) panel is a sub panel feeding from a 100amp fuse in the main panel. As I understand it the only other way of feeding the studio it's power would be to give it it's own service. And as I understand it that is fruitless since it would come directly from the same power transformer sharing all of the same power. My father who wired the studio thought so also. He has been an IBEW licensed electrician for 35 years now although I have yet to call him and ask him what he thinks of the problem.


The two different types of outlets in the studio(all on one sub panel)are to simply separate the grounds from common lights and computers from the audio equipment which is on isolated grounds. All of the power grounds from the isolated outlets feed back to a ground lug bar on the sub panel which has a plastic riser to separate the isolated grounds from the common ground. This feeds straight to earth. I have seen and worked in lots of studios that use this grounding scheme so in this case I'm not quite sure why this is strange.


On the Manley I lifted the power ground and the problem actually got worse. Some of the guitar amps that have had the problems didn't have grounds. Today the problem came from a standard Fender Blues Jr.

As for the radio station that is a great idea. I will throw the Manley up tomorrow and listen to some of it and find out.

I will do some research on the RFI filters this may be my only option.

Thanks again,

Steve

[David Kulka]

It would be helpful to find out what radio station it is, whether AM or FM, and your distance from the station's transmitter.

Isloated ground power is common in studios and usually works well. You have two ground systems -- "quiet" tech power, which all the studio gear is plugged into, and "dirty power", that everything else is plugged into. Just don't mix them.

Even if everything is wired perfectly at your studio, you might have RF problems if the transmitter is very close by (5-10 miles). In that case ferrite beads or RF filters might be useful.

If the station is further away (lower RF field strength levels at your studio) your gear or wiring may be at fault. If it only happens with the Manley, some kind of small filters may be the answer. If it happens with various pieces of gear, maybe the AC power wiring or audio wiring needs another look.

[guitarbill]

Originally Posted by primalsteve

Thanks for the feedback. To clear up a few things here's the setup.


The main 200amp panel is the main panel for the home. The studio(seperate building) panel is a sub panel feeding from a 100amp fuse in the main panel. As I understand it the only other way of feeding the studio it's power would be to give it it's own service. And as I understand it that is fruitless since it would come directly from the same power transformer sharing all of the same power. My father who wired the studio thought so also. He has been an IBEW licensed electrician for 35 years now although I have yet to call him and ask him what he thinks of the problem.


The two different types of outlets in the studio(all on one sub panel)are to simply separate the grounds from common lights and computers from the audio equipment which is on isolated grounds. All of the power grounds from the isolated outlets feed back to a ground lug bar on the sub panel which has a plastic riser to separate the isolated grounds from the common ground. This feeds straight to earth. I have seen and worked in lots of studios that use this grounding scheme so in this case I'm not quite sure why this is strange.


On the Manley I lifted the power ground and the problem actually got worse. Some of the guitar amps that have had the problems didn't have grounds. Today the problem came from a standard Fender Blues Jr.

As for the radio station that is a great idea. I will throw the Manley up tomorrow and listen to some of it and find out.

I will do some research on the RFI filters this may be my only option.

Thanks again,

Steve

As for the sub panel grounding issue: look at the heavy copper ground lines going to your ground rods. I'm assuming you have ground rods at the sub panel? It sounds like you may want to verify this and keep in mind this: one rod at the sub panel does not meet NEC code. I am thinking that if you have "isolated grounds" that you may need two rods for each to meet code. Was the electrical inspector by to look this over?

gb

[primalsteve]

Originally Posted by guitarbill

As for the sub panel grounding issue: look at the heavy copper ground lines going to your ground rods. I'm assuming you have ground rods at the sub panel? It sounds like you may want to verify this and keep in mind this: one rod at the sub panel does not meet NEC code. I am thinking that if you have "isolated grounds" that you may need two rods for each to meet code. Was the electrical inspector by to look this over?

gb

The Sub panel itself shares earth with the main service. This is the original earth ground located at the homes main panel. The isolated ground comes of the sub panel and meets earth about 5' away from the panel. I drove this into the ground it is only about a year old. 1/2 copper about 6' in length.

Thanks again for the input.

[primalsteve]

Originally Posted by guitarbill

As for the sub panel grounding issue: look at the heavy copper ground lines going to your ground rods. I'm assuming you have ground rods at the sub panel? It sounds like you may want to verify this and keep in mind this: one rod at the sub panel does not meet NEC code. I am thinking that if you have "isolated grounds" that you may need two rods for each to meet code. Was the electrical inspector by to look this over?

gb

Oh yea and codes approved it but that doesn't mean a whole in TN.

Steve

[primalsteve]

I just went and bought a set of the XCC XLR connectors from Neutrik. They are supposed to be unbelievable at reducing RF. I'll let you guys know how it goes. If I get a chance maybe I will record the difference of the mics noise floor.

Steve

[Matt Syson]

Hi
If it is one radio station (or a couple) find out the frequency it is transmitting on.
ALL conductors are an aerial so in a sense if your 'ground' cable is aproaching the wavelength of the transmission (or multiple) you may not actually be 'grounded' at all. The grounds on the mains incoming are there only to reduce the chance of getting killed when the mains gets shorted to the chassis of your gear (toaster etc) and as such has no real value at RF. I heard a tale about problems with a unit picking up RF for which the solution was found to be 'cut 1 foot off the mains cable', as it then detuned the 'reception'.
Ferrite beads or the little 'clamp around the cable' types should help a bit.
I had a power amp that was failing because it was used near a transmitter. The INPUT was fine but the speaker cabling was bringing the RF in which was upsetting the amp making it oscillate and take the fuses out.
Best of luck
Matt S

[primalsteve]

Ok so I got the RF filter XLR's from Neutrik and it actually considerably increased the problem. I tried switching to one of my outlets that are my common outlets in the studio and the problem stayed. These outlets share earth ground from my main home. Ground lift did nothing.


Here's where it gets interesting. When I initially unplug the tube mic if I touch any of the prongs of the plug against the metal outlet cover the radio noise comes back. Eventually when the mic is completely powered down it goes away.

More interesting: When I bring the mic into my main home and switch back to a normal mic cable the noise is also gone.

So to recap.

1. Noise present in studio (isolated ground outlets)
2. Noise present in studio (normal outlet sharing homes ground)
3. Noise not present in home outlets with a normal mic cable.
4. Noise slightly present in home with RF filter mic cable
5. Upon mic powering down when touching any prong of the power cable to the metal outlet cover noise is present.

Sorry to be redundant

[Matt Syson]

Hi
So it means that the mic amp INSIDE the head is demodulating the radio, which in a way is not suprising but disappointing. In most phantom powered (or tube) mics, the actual amplification happens in the mic itself right next to the capsule rather than the supply box.
Mic amps should have filtering to remove everything above say 50KHz to prevent this sort of nastiness
Again, identification of the interfering signal would help, is it a local radio station or taxi or what?
Matt S

[primalsteve]

Originally Posted by Matt Syson

Hi
So it means that the mic amp INSIDE the head is demodulating the radio, which in a way is not suprising but disappointing. In most phantom powered (or tube) mics, the actual amplification happens in the mic itself right next to the capsule rather than the supply box.
Mic amps should have filtering to remove everything above say 50KHz to prevent this sort of nastiness
Again, identification of the interfering signal would help, is it a local radio station or taxi or what?
Matt S

I listened today for about 45 minutes to try and get the call leters but they never gave them. It's a Chiristian station and for almost an hour today I listened to a pastor speak about how to more effectively please you lover. Huh? :-)


I will plug in again tomorrow to see if I can get the call letters.

[Barron43]

Seriously, I feel your pain man. I just plugged up a new tube mic and *voila* Tejano in my signal path. Following the steps the other folks have laid out I've narrowed it down to coming from the mic itself. It seems to be an FM station @ 102.9.... any ideas??

[Matt Syson]

Hi
Within FCC regulations (and others in different countries) ALL equipment should not cause interference with other equipment OR be susceptable to interference from external sources. (I can't be bothered to write out the full rules).
There are limits set down because obviously running a high powered interference source and having a very sensitive instrument right next to it would be technically impossible. It is legally binding for the problem source to sort it's act out if it causes problems for others. In a similar vein, equipment must have some level of interference rejection. First off, call the mic manufacturer and say you have a problem giving them as much information as possible, like the frequency of the radio station in this case, and the distance you are from it's TRANSMITTER AERIAL.
with some luck you should get the mic 'fixed'. As a second line, call the FCC and say you are having a problem with a local radio station 'breaking in' to varoius bits of audio kit. The fact that it does so on several units may suggest that the transmitter aerial is inapropriately sited. Talk to neighbours and ask if their audio kit (Hi Fi etc) is affected. With a bit of luck you may get the FCC boys round with some measuring equipment to identify the source and decide whether it is excessive. Failing this, it is down to wallpapering your studio with heavy grade aluminium foil or moving house.
You have played with ferrite beads and fancy connectors so now try the ideas above.
Matt S

[guitarbill]

Originally Posted by Matt Syson

Hi
Within FCC regulations (and others in different countries) ALL equipment should not cause interference with other equipment OR be susceptable to interference from external sources. (I can't be bothered to write out the full rules).
There are limits set down because obviously running a high powered interference source and having a very sensitive instrument right next to it would be technically impossible. It is legally binding for the problem source to sort it's act out if it causes problems for others. In a similar vein, equipment must have some level of interference rejection. First off, call the mic manufacturer and say you have a problem giving them as much information as possible, like the frequency of the radio station in this case, and the distance you are from it's TRANSMITTER AERIAL.
with some luck you should get the mic 'fixed'. As a second line, call the FCC and say you are having a problem with a local radio station 'breaking in' to varoius bits of audio kit. The fact that it does so on several units may suggest that the transmitter aerial is inapropriately sited. Talk to neighbours and ask if their audio kit (Hi Fi etc) is affected. With a bit of luck you may get the FCC boys round with some measuring equipment to identify the source and decide whether it is excessive. Failing this, it is down to wallpapering your studio with heavy grade aluminium foil or moving house.
You have played with ferrite beads and fancy connectors so now try the ideas above.
Matt S

Matt, You're right about what the law says, but the FCC hasn't responded to interference calls in a meaningful way in this country since deregulation and the insuing massive budget cuts that followed (this got much worse about 15 years ago). The only way you'd ever get them to show up is if an entire major population was affected by source transmitter splattering rf everywhere, IMHO.

primalsteve: It's not real hard or expensive to add a rod (or tie your isolated ground rod to the sub panel ground) at your sub panel and you should do this for your own peace of mind because it is code. I looked this up again yesterday and at a sub panel it is a great idea. Consult with an up to date licensed electrician who knows the newest NEC. You don't want to hear what the judge says if, god forbid, someone gets shocked and tries to sue and your sub panel is found to be out of compliance. As for the RFI, putting the rods to code may help. The fact that the noise goes away in your house bears this out. Grounds are hard to prove without being trained on what is referred to as a "four wire ground tester" or something like that. Instead for about $40 you can buy the 8' 1/2" copper plated rod and NEC approved connector for it ( place it 6' from the other one ) tie all your grounds together and see if that helps. If not, at least you're to code; something your insurance man will appreciate if no one else.

Did you try an RFI endowed UPS, power strip or furman/monster power conditioner or isolator yet?

The Faraday cage as described by Matt in his post works best with a layer of copper and mu metal with ground rods palced every two feet around it's perimeter.

gb

[Matt Syson]

hi
I could start on about governmental hypocrisy or something but that can wait...
Yes sort out a ground rod your setup must at least be safe to 'code' standards.
It is still worth a 'friendly but firm' call with the mic manufacturer, there may have been mods made to later units which could help.
Matt S