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I wish my wife was as dirty as this mains supply |
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shagnasty 
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Joined: 30 July 2007 Location: Guildford, UK Status: Offline Points: 7685 |
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 Posted: 23 March 2017 at 1:55am |
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Buy and X32 and a S16!
I doubt you will get AM interference on a AES-50 line... I real terms you are screwed, neutrik connectors will not make a shit of difference, I doubt steel conduit will either (also if you try it for God's sake use EARTHED 50x50 Galv trunking, don't spend a day removing all your XLRs to thread your core into a 32mm Screwed steel conduit. What you need is a faraday cage, but if the interence is really coming in thru the mains that won't help either. First think have you run mains from the to your FOH desk, if not do so, a lump of 4mm flex from your main distro will remove possibly a 100m of ring main cable from your rig, are you using a mains distro, if not hire one, run a 16mm feed from the biggest baord you and find and plug everything into that, the stiffer you can get your mains, the better "50Hz to AM ratio" you will get, you may also want to look at running all your processing and desk off a 110V supply if it can be switched to 110V as a building site type transformer (get a 3KVA metal one NOT a Plastic sand cooled one with a duty cycle of 15mins!!!) has very poor frequency couple above a couple of hundred Hz and will attenuate you AM signal quite a lot, this is cheap to try as you can hire a tranny from Speedy hire or similar. If you know how to do it put a spectrum analyser on the mains and see if it is truly come in the through that, if it is, call the Sparky Board as they obliged to give a certain quality of mains power and may be able to re-route or re-jig the supply to improve things. putting the desk on stage will tell you if your core is coupling, if it is your 30M core a rack of ADA-8000s or Presonus D8s on stage will let you shoot line level to your desk which will be less susceptible to interference than mic level... If no buy an AM receiver, tune in and drop an out-of phase version into the mix to cancel it out!!! |
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MattStolton
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Joined: 04 September 2010 Location: Walthamstow Status: Offline Points: 4234 |
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Posted: 23 March 2017 at 10:51am |
Had to quote that again - has to persist into the SP sub concious.....too many jokes.... I used to pick up Radio 5 Live, when touching each end of the crossfader on a Kam GMX5, useful for the football results.
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Matt Stolton - Technical Director (!!!) - Wilding Sound Ltd
"Sparkius metiretur vestra" - "Meter Your Mains" |
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nev23
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Joined: 08 September 2008 Location: Taunton, UK Status: Offline Points: 99 |
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Posted: 23 March 2017 at 11:02am |
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Interesting comments.
I have been a transmitter engineer. So I know how to do this. I worked briefly on Radio Caroline. They had a 50kW and two 10kW transmitters feeding a mast in very close proximity to the studios. Admittedly the steel hull helped a bit. CMRR won't help you. None of the audio circuits have any useful CMRR at radio frequencies. They should have r.f. filters, which will hopefully block these relatively low frequencies, as well as mobile phone frequencies, but you will have to suck it and see, one piece of equipment at a time. Mains cables may be a problem, but are less likely. Extra shielding may help, but will need to be correctly earthed; this may end up being more trouble than it is worth. Just remember: every cable is an antenna. Start with the amp rack on and connected to speakers, but no inputs. Is everything quiet? If not, you will need a mains filter. Modern amps with switch-mode PSUs will be very good at rejecting mains borne interference. Then connect the input cables to the amp rack and the mixer, but leave the mixer switched off. Is everything quiet? If not, you need input filtering in the amp rack. Then switch on the mixer with no inputs connected. Quiet? No? Then the mixer needs a mains filter. You can go through the whole system in this way until you isolate the problem equipment, lead or connector. You may find certain DI boxes will solve problems, while others will cause them. Many guitar amps have poor input filtering. Amps with DI outs may still need a DI box. Filters can be simple and cheap and still be effective. Starquad is good, but not always necessary, even here. Some pieces of equipment, even modern expensive stuff, may simply be unusable in this environment. Especially if it has inputs that work at very high bit rates. |
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snowflake
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Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3122 |
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Posted: 23 March 2017 at 11:43am |
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some people recommend disconnecting the shield from pin1 at the male end of xlr interconnects (not mic leads or multicore) - does this help stop the shield acting as an antenna?
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nev23
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Joined: 08 September 2008 Location: Taunton, UK Status: Offline Points: 99 |
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Posted: 23 March 2017 at 12:06pm |
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No because the cores will still act as an antenna, and/or the rf current in the shield will transfer be coupled to the cores.
The shield does help with rf and mains interference, but may make earth loop problems worse. |
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studio45
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Joined: 16 October 2007 Location: United Kingdom Status: Offline Points: 3864 |
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Posted: 23 March 2017 at 1:57pm |
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Thanks guys, gonna go back in today armed with more knowledge and some filtered power strips. Hopefully we can find a way.
With the building interior being listed to some extent, and budget being minimal (when is it not....) a lot of the shielding ideas can't be done. The 110v transformer idea is one I can try. I have a couple of yellow plastic jobbies. So not gonna try them on the bass amps, but the desk and signal processors could use them. Just look the other way while I put a yellow Ceeform on the end of a 4x13A strip  When this building stopped being a cinema in 1975, I'm not sure if the transmitter was operating. Since then, it hasn't been regularly used for large scale sound reinforcement - it was a shop for years, then just occasional film screenings and theatre events, for which pretty high-end gear was rented in and then taken out again. I assume they found a way to mitigate, but then, they probably didn't have to deal with 16 mic-level channels plugged in at the end of a 30m antenna every show. There is another venue in the basement, where I have done a few gigs. You can get this issue down there, but much less severely - never in the PA, only in very high-gain guitar amp setups, and then, a filtered power strip cures it. I think this is due to the several metres of actual earth and concrete around the walls providing a shield. On the above-ground floors - no such help....
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Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA
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minaximal
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Joined: 26 September 2004 Location: United Kingdom Status: Offline Points: 1780 |
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Posted: 23 March 2017 at 2:17pm |
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If using an Isolation Transformer does work, you can get them made to any spec, I use a 230v on the barge from here:
*Edit. Oh and they make filtered power supplies too.
Edited by minaximal - 23 March 2017 at 2:26pm |
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madboffin
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Joined: 03 July 2009 Location: Milton Keynes Status: Offline Points: 1538 |
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Posted: 23 March 2017 at 4:17pm |
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One thing to note is that it's sometimes possible for amplifiers to pick up RF on the speaker leads too.
Following nev23's advice and working backwards through the system is the way to go... If you are unfamiliar with how radio works, the main thing to understand is that anything in the audio chain that acts as a rectifier (diode) can extract the audio from an AM signal. In effect, it causes intermodulation between the various components of the radio signal, some of which is the original audio programme which then gets amplified like any other audio voltage. So if the RF signal is big enough to cause clipping or overload anywhere in the audio electronics, you will end up with a radio receiver. Minimising the amount of RF getting into the the equipment (it can be carried on any wiring that enters it) is the first line of defence. The next is to use low pass filtering on the affected inputs, to stop the RF whilst still passing audio. |
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shagnasty
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Joined: 30 July 2007 Location: Guildford, UK Status: Offline Points: 7685 |
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Posted: 23 March 2017 at 5:21pm |
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Nev23 Put things in a very coherent way and is definitely right.
If you do try with a 110V bucket as a filter for your system making a 110V > 240V lead is fine (I've have a few 240V plugs with the bump filed off so I can plug them into 110V supplies but remeber what I said about Plastic 110V transformers being sand cooled and having a continuous rating of about 5% of the stated VA, 1 3KVA bucket won't hold up a 200W lamp all night, but if it work you can buy an air-cooled metal box one. Nev23's detailed work back from the amp rack is solid advice, but you make make the horrible discovery no one part is at fault, it is a cumulative effect, if you buy filtered power kit, keep the receipt in case they don't work, most are designed to remove noise at 10s of KHz not just a few, hence won't offer that much attenuation at am frequencies, again they also aren't designed for 100% duty cycle (they work by effectively shorting out teh interence by offering a low-impendance path above mains frequency, this is fine for the odd spike or taxi radio, but they won't be engineered to dump several watts continuously from a multi KW transmitter sat next door, cheap plastic = BAD lumpy metal is better! Please post how your research goes....
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Guests
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Posted: 23 March 2017 at 5:57pm |
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what is the transmitter transmitting?
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madboffin
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Joined: 03 July 2009 Location: Milton Keynes Status: Offline Points: 1538 |
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Posted: 23 March 2017 at 7:48pm |
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It's AM broadcast. Two transmitters combined into one aerial.
BBC Radio Sheffield 1035 Absolute Radio 1233 Edited by madboffin - 23 March 2017 at 7:49pm |
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midas
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Joined: 27 October 2011 Location: Cumbria Status: Offline Points: 2117 |
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Posted: 24 March 2017 at 10:09am |
Oh did you now....lol. Does the wife know??? |
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In bass no one can hear you scream!
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kedwardsleisure wrote: