Radio Interference

[cheddatom]

We've always got the radio coming through guitar amps in my music room. I've been recording here for a while, but it's normally pretty loud stuff. Anyway, the other day I did some acoustic stuff and you can really hear the radio coming through.

It's only on mics i've run through my desk. I use a seperate rack of pres for my condensor mics, and there's no radio interference on these.

Any ideas on what to do?

[Shire]

That's bizarre, we have a strange problem at our local practice rooms where the vocal mic from one of the other practice rooms comes through our guitarists amp. Annoying but not as annoying as your problem! Good luck getting it sorted

[cheddatom]

Cheers.

Just to try and clear it up a bit - I get the radio through guitar amps and PAs etc anyway. I can normally get around this when recording. However, now it seems it's been coming through my mixer all along, which is no good when I want to record acoustic stuff.

[OldG]

You could check your mixer,amps etc have got decent earth connections - and the power sockets you are pluggng into while you are there... S'where I'd start - then go to leads and interconnects ( I have a speaker lead that sounds like an old dial-up modem if my laptop is too close, for instance).

[phil.i.stein]

some interesting info here, particularly regarding mics.

[url="http://www.alectrosystems.com/tips/audio_tips/audio_tip_RFI.htm"]http://www.alectrosystems.com/tips/audio_t...dio_tip_RFI.htm[/url]

[BOD2]

[quote name='phil.i.stein' post='1027766' date='Nov 18 2010, 11:28 AM']some interesting info here, particularly regarding mics.

[url="http://www.alectrosystems.com/tips/audio_tips/audio_tip_RFI.htm"]http://www.alectrosystems.com/tips/audio_t...dio_tip_RFI.htm[/url][/quote]

That's a good step-by-step guide to indentifying the problem.

Except the last part where it suggests disconnecting the AC ground to break a "ground loop". Don't ever do this. You might kill someone !

[OldG]

[quote name='BOD2' post='1027811' date='Nov 18 2010, 12:02 PM']Except the last part where it suggests disconnecting the AC ground to break a "ground loop". Don't ever do this. You might kill someone ![/quote]



This is a never ever type bodge - also a big part of my previous post....

[cheddatom]

Thanks, i'll watch those videos tonight.

[phil.i.stein]

[quote name='BOD2' post='1027811' date='Nov 18 2010, 12:02 PM']Except the last part where it suggests disconnecting the AC ground to break a "ground loop". Don't ever do this. You might kill someone ![/quote]
good point. although over-exposure to radio Stoke may well achieve the same result, albeit more slowly and painfully.

[Slipperydick]

Any cable thats earthed at one end is in effect an aerial. Unfortunately, this applies to the screen on pretty well any Mic or guitar lead, patch lead etc. sometimes worse if the cables are coiled up. Balanced cables are far less likely to be the culprits, but if it is being picked up by the screen, it could be anywhere.

You could try these, [url="http://www.maplin.co.uk/module.aspx?moduleno=32792"]http://www.maplin.co.uk/module.aspx?moduleno=32792[/url] they only cost a few pence each, so no great loss if it dont help.

Try and be methodical though, and see if you can work out where its actually being picked up. Apart from the leads above, its possible that its being picked up in a mains cable, or just about anything else, including internal wiring in the equipment itself.

There is a lot on interweb amateur radio sites regarding RF interference, always worth a look.

Edited November 18, 2010 by Slipperydick

[cheddatom]

What would I do with the ferrite rings?

What's weird to me is that it seems I can run the exact same chain but using my rack of pres instead of my desk, and it's radio free. The desk is a cheap POS I bought off here for £20ish so perhaps it's that?

[flyfisher]

[quote name='cheddatom' post='1027906' date='Nov 18 2010, 01:33 PM']What would I do with the ferrite rings?[/quote]
Run your signal wires through them and they attenuate any Rf signals. Computer cables often have such things fitted to then to reduce their own RF emissions (as required by various EMC standards).

However, in practice, you'll probably find these types of ferrites easier to use:
[url="http://www.maplin.co.uk/module.aspx?moduleno=32799"]http://www.maplin.co.uk/module.aspx?moduleno=32799[/url]

[cheddatom]

OK, thanks!

[Slipperydick]

[quote name='cheddatom' post='1027906' date='Nov 18 2010, 01:33 PM']What would I do with the ferrite rings?

What's weird to me is that it seems I can run the exact same chain but using my rack of pres instead of my desk, and it's radio free. The desk is a cheap POS I bought off here for £20ish so perhaps it's that?[/quote]

There are a few types, some you thread the cable through, some you thread in and out twice, some clipover the cable( the type probably fitted to tyour PC monitor etc ) just follow the instructions that are with them, Dont bother asking the Maplins staff, theyre usually - not always -anoracks who know less than they think. Plenty on the interweb about them. some types work better than others depending on various things such as frequency, length of cable, strength of the signal, impeadence etc..

[url="http://www.stevelarkins.freeuk.com/computer_interference.htm"]http://www.stevelarkins.freeuk.com/computer_interference.htm[/url]

Edited November 18, 2010 by Slipperydick

[BigRedX]

Do they affect the signal in the cable in any way?

[cheddatom]

Don't get me started on maplins staff, or their website, or their prices, or the junk mail or....

[icastle]

[quote name='BigRedX' post='1028080' date='Nov 18 2010, 03:57 PM']Do they affect the signal in the cable in any way?[/quote]

Nope.
All they do is capture stray signals and convert it into heat.
The original signal is not in any way attenuated.

[icastle]

[quote name='cheddatom' post='1027906' date='Nov 18 2010, 01:33 PM']What would I do with the ferrite rings?

What's weird to me is that it seems I can run the exact same chain but using my rack of pres instead of my desk, and it's radio free. The desk is a cheap POS I bought off here for £20ish so perhaps it's that?[/quote]

Perhaps the desk is more sensitive to the frequencies being erroneously received than the pre-amps.

[icastle]

[quote name='BOD2' post='1027811' date='Nov 18 2010, 12:02 PM']That's a good step-by-step guide to indentifying the problem.

Except the last part where it suggests disconnecting the AC ground to break a "ground loop". Don't ever do this. You might kill someone ![/quote]

Yes indeed.
I think what they're probably [b]trying[/b] to say is that if one pile of equipment is using a different earthing point from another pile of equipment from another pile of equipment, then connecting the two piles of equipment up together will create the opportunity for interference.
What they are saying is correct - disconnecting the earth on one pile of kit may solve that problem but create a potentially hazardous environment in which to work in.

Try using a hefty multiway trailing lead and run kit from the same mains source - if that removes the interference then you've at least identified what the problem is.

I do know that there are devices on the market that provide a safe earth lift/isolation but I've not tried them and haven't studied the subject closely enough to be able to comment with any expertise.

[BigRedX]

I would suspect the mixer. What is it?

[cheddatom]

heh, I don't know, i'll take a picture later. It's not a well known brand, put it that way!