I wish my wife was as dirty as this mains supply

studio45 wrote: Now then, mains power gurus: I've just installed my rig in a venue that's right next to an AM radio transmitter. Like 20 metres away across the back yard. 30m multicore+power has to be deployed down one wall nearly parallel to the antenna, and long XLRs are often connected to the stage box. Less than ideal. As long as everything's properly grounded there are no big problems. You can faintly hear some speech with your ear right next to the tweeter horns. However, when any cable with even a slightly dodgy ground is used, the radio stations come through loud and frickin' clear. But intermittently. It is *maddening*. Obviously all my cables are as good as they can be, but, well.....I couldn't afford Neutrik on everything  The transmitter sends at 1035 and 1233 kHz. I think I need to filter the mains supply. What would be the best strategy? Big filter in the consumer unit, or smaller filters/ filtered power strips for the line-level gear? Cheers :)

Is every single connection in your setup balanced? That is your best immediate defense.

Yes, all interconnects balanced. There's just so much field strength it is testing the CMRR of *everything*. And if a wobbly connection goes unbalanced, or un-grounded, you know about it right away.

I've used small mains filters in the past to cure guitar amps of this problem. That's why I think it might be the solution again. Just not sure if I need to spring for the expensive high-current DIN rail modules and a sparky, or if cheaper local filtering for the low-powered signal processing gear is a valid option. I mean, the wiring might just pick up more RF on the way from the breaker board to the stage - there are some long cable runs.

Oh I feel for you. Mobile Disco days in the 70's in pubs near Heathrow. Citronic Avon airport radio model.

Must be this one, a kilowatt or so into an old-school bit of wire off a factory chimney...

http://tx.mb21.co.uk/gallery/sheffield-mf.php

Was this a one-off (too late now) or a regular gig?

A few notes to get you thinking:

It's more likely to be getting into signal cables than the mains supply.

For RF immunity the cable screening has to be very good, so it's worth checking none of your pin 1 connections have pulled off.
Also, any poor or oxidised connection can become a rectifying junction and behave like a 1920's crystal radio set (look up the "rusty bolt effect").

Track down which piece of equipment - mixer, system controller, DJ console (most likely) is picking the signals up, and report back.

Some modern kit has no immunity and the only way to fix it is to add filtering to its inputs and outputs.

These things can be cured, but usually only by people with both Audio and RF systems experience.

An "earth" at radio frequencies isn't the same as an earth at 50Hz.

kedwardsleisure wrote: I used to pick up minicab drivers with my organ

Just reposting your comment for posterity; You'll probably want to delete it when you read it back 😅