KEF PSW 2000 erratic popping / thumping noise when there is nothing playing

Hello, I have a slight issue with my KEF PSW 2000 subwoofer.

There is a popping / thumping noise when there is nothing playing or when there is no sub-bass to be played (a dialog scene with no background music or sound for example). I would say it sounds something like a heartbeat and isn’t very loud. It is very erratic and can be pretty annoying.

It is the same on both “auto” and “manual” mode. I also found out that the subwoofer does this even when it is disconnected from the receiver. I am thinking that it may be related to some electrical interference in the grid, but also I don’t know anything which could cause such interference in my place.

I also read about some faulty capacitors which tend to fail on this model, but that often results in some kind of loud buzzing which I am not getting (My subwoofer actually works well when it is playing something).

Has anyone faced a similar issue and if so, do you know how to mitigate it?

So you only get this sound when the sub is plugged in, but not playing anything? This sounds to me like either RF or electromagnetic interference or possibly a power supply issue. I think it’s more likely to be an interference issue though. Have you tried plugging it into a socket in a totally different room with nothing else plugged into that socket to see if the sounds you’re hearing continue? That’s where I would start.

Also, right now are you plugging it directly into the wall or are you using some sort of surge protector, power strip, etc?

That’s right. It’s only when nothing is playing or when there is no bass in the scene so the sub doesn’t have any work to do. Normally, it is plugged into an extension cord along with all the other AV related equipment, but I already tried plugging it into a different socket. I also tried a different room, but the sound was still there, although maybe a little different.

Also, I have a feeling that it didn’t do this when I bought it around two months ago. But it may also be just me not noticing it before, even though it is really noticeable so again, I’m not sure.

Here is a recording I took:
This is the worst case scenario as I cranked the input level knob to maximum and also the sound is not nearly as loud in real life, but I think it demonstrates the characteristics pretty well.

It can also not happen for multiple minutes and then it just starts. I also have a feeling that it prevents the subwoofer to go into standby mode if it is set to “auto”.

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Interesting. It sounds to me like something electrical is putting stray voltage through to the sub causing those sounds. As to what it is, I have no clue. This may seem like a stupid question, but can you tell if it’s happening in the background even during times when the sub is putting out bass? Knowing whether or not it’s doing it all the time or only when no audio signal is passing through to it might be helpful in narrowing down what it could be.

That said, if you only bought it a couple months ago I’d check in with their support and possibly RMA the sub, get a new one, and hopefully live happily ever after.

I’m not 100% sure, but I would say it’s not happening when it’s playing anything. Everything seems very clear when it’s outputting something.

I bought it used from a guy on marketplace so that isn’t an option.

This right here makes me think it’s an issue with the crossover. As in something’s not muting properly when the sub isn’t engaged to be playing, creating some signal bleed which is causing electrical noise to reach the driver. Honestly though, that’s speculation based on what you’ve told me. Let me ask this, when you’re playing the same material through your system (the same movie or music), that isn’t triggering the sub, does the noise that occurs during that part sound the same every time? So lets say that you know when you play X movie that from 3:12 to 6:24 is a section that doesn’t use the sub. When you play that section multiple times is the sub creating the exact same noises each time?

I can try it, but I don’t think it will be so. It’s also doing the noise even if the input from AVR is disconnected completely. I don’t think it’s related to the signal from received. Probably and more likely it’s actually a lack of the signal.

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I forgot about the part where you said it does it even if it’s disconnected. That sounds like and power supply issue if it isn’t an issue with RF/EM interference. I looked it up and it does seem like this particular model (PSW2000) is known for the amp and internal mains power supply having issues or dying. You could try a different power cable if you have one on hand. A power conditioner or linear power supply might solve the problem if it’s due to something like some DC getting through.

Yes. It’s true that there are some issues with this particular model. However, when looking for it online I almost always found people getting some kind of constant and very loud buzzing due to some capacitor not working properly. I already tried a different power cable from my computer. Sadly, that didn’t help.

I didn’t find much about the issue that I’m having so I’m clueless about what to do. Linear power supply doesn’t sound like a proper solution in my opinion, especially if the problem is going to get worse and I guess that is also expensive, maybe more than the sub itself.

It would be better to repair the sub itself if possible, but I’m not sure about what is causing it. I may just risk it and replace the problematic capacitors and see if that helps, but that may also change nothing.

Are you handy with a soldering iron as all? If so I could probably walk you through replacing yhe capacitors over a video call.

Yes. I have a soldering iron. I have been using it mainly for connecting wires and such. I didn’t really do board repairs, but I think I can manage it. Anyway, I would need to buy the caps first.

Thanks for the offer. We can arrange when those caps arrive as that would probably take some time.

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Okay, just PM me if you need so help on it.

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Do you think I should start with a visual inspection? I guess that a faulty cap should be visible, shouldn’t it? I need to know which one(s) I have to buy for the replacement.

Any tips for the disassembly? I have an anti-static bracelet from ifixit, but don’t know if there is some procedure to discharge it first or something like that.