speaker hum

[Pe7e]

I've got a Numark CDN88 Player coupled to a CDM 200 mixer that produces a low level hum when no music is playing, if I slide the master volume up (with no music playing) to near max, the hum reduces considerably, but returns when it's turned down again. The speakers are quiet with other sources connected, any ideas anyone? do you think fitting one of THESE (http://www.ebay.co.uk/itm/8Pcs-Cylindrical-EMI-Suppressor-Ferrite-Magnet-Core-Filter-8mm-Power-Cable-/291157929529?tfrom=291050548519&tpos=top&ttype=price&talgo=undefined) to the power cable of the mixer/CD player will help?

[funktions]

sounds like a mains earthing issue, might be worth using a piece of wire to go between the metal work of the CDN88 Player and the CDM 200 mixer and onto the amplifier, if this cures it then I might be worth looking to see if you can run balance cables between all 3 of them. normally arises when an unbalanced cable uses its outer core to also be an earth between the devices.

[Nakatomi]

If the hum comes through your headphones as well as through the PA, then it's likely an issue with the line cables between the CD player & mixer, or else the player or mixer has developed a fault where a ground has become open. It could be either since a lot of manufacturers tend to use flimsy ribbon cables to join boards together these days.

On the other hand if it's only out of the PA, then try (if not already doing this) plugging the PA into the mains as close to the playout gear as possible, oh and check all your extension cables to make sure the earth is continuous. A discontinuity in mains earth can produce hums and be very dangerous indeed.

[Pe7e]

Thanks for the replies so far chaps, it's appreciated. The extensions and power cables have both recently been PAT tested and have also been swapped to eliminate them anyway, also, the player, mixer and active speakers were connected to the same 4 gang extension. The player/mixer has been hooked up to a totally different PA in a different location, but had the same fault. I've also swapped out the mixer for a less well spec'd mixer (still a Numark) and the hum ceased to be a problem, so I'm reasonably sure the fault lies within the mixer or the wiring. I've noticed if I turn the player unit off the hum reduces but doesn't disappear. :confused: I have managed to get my hands on a set of interconnects which connects the drawer unit to the player control unit, I will try swapping these when the player is returned. I've not noticed whether or not the hum is present in the headphones, but will also check this out when the player is returned.