I’ve had a Kef Active sub for about 15yrs or so. Its done me a great service over the years. It has an auto mode so its turns itself off and switches on automatically as soon as it detects an input. It has started to produce a hum noise. It starts off from a level of no noticeable hum then the hum starts off very quiet and gradually gets louder over the course of about 20 or so minutes (sometimes longer) to a fairly loud and noticeable hum. After 10 seconds or so at its loudest volume it suddenly stops and goes quiet again (i.e. no hum at all) and the cycle starts again. Other than the hum it appears to be operating properly.

I don’t think its an input issue as if I unplug it from the amp it still happens so appears to be an issue with the unit itself. I’ve not tried plugging it into a different power point.

Any ideas? Cheers.

1. It’s aliens trying to communicate with earth I suggest you call the alien squad
Or
2. It’s the inbuilt chip put in from manufacture to start doing this annoying hum so you go and buy another one.

I like the alien idea. How better to attempt first contact with the human race? Though I’m sure the human race would be better served if they made first contact with someone better qualified than me. I’d be more likely to take down to my local pub than start to engage in a conversation about how interstellar travel is possible, or what’s the secret to a clean limitless supply of energy.

I suspects it’s something inside that’s gone, just wondering if it’s fixable. Hopefully the symptoms are recognisable to anyone with some rudimentary electronics knowledge.

What has changed? Have you moved anything, changed what it’s plugged into, stuck other items on a 4 way, changed amp etc?

Does it happen with the components plugged in? – try standing it alone not plugged into anything else and see what you get there

Could be a simple earth loop somewhere, but as it’s rising and peaking it sounds like it could be a capacitor fault – but rule out earth hum first, 9 times out of 10 that would be a likely cause.

My Yamaha sub did something similar a few years ago.
It turned out that the phono cable had ‘cracked’ and take some of the stands with it due to a very tight turn unto the socket on the receiver.

Do you have another cable to hand just to rule it out as a possibility ?

Hope you get it sorted.

Is it a kef psw2010 or similar?
If so checkout http://lug.demon.co.uk/kefrepair/

I had problems with mine which I was unable to repair myself. I sent it off to the bloke on the website on my previous post. He repaired it and sent it back for me to check before invoicing me. It cost about £30 and has been faultless since. I think the problem partly comes from the auto shut off mode you mentioned not actually shutting the amp off but only muting it. The amp thefore burns itself out. You are probably lucky to have got 15 years out of it,
If it’s not the model I mentioned on the previous post it may be worth contacting him anyway. He repairs them for a bit of beer money and because he enjoys it.
Andy

Nothing with the setup has changed but the phono cable isn’t the best so maybe I’ll try that anyway. I have unplugged it from the amp and it still did it which is why I ruled out the earth loop issue, and with my very basic electronics knowledge I thought it might be a capacitor issue with the rising and falling nature of the hum, like the capacitor charging then discharging, but not sure if this is due to a hard fault or some other interference related issue. I’ll go round it again.

It’s not a PSW2010, it’s an earlier model..it’s the model 30b, but is probably very similar to the PSW as it’s a good old fashioned big ass woofer connected to a powerful amp. I’ll take a look at the PSW fixes too.

Cheers.