Getting Rid of Interference

[paulrockliffe]

I've got my PC plugged into an Amplifier, I get ground loop interference that comes and goes that I've been tolerating. But yesterday I got a new keyboard that has LED back lighting, If I turn the brightness right up I get a high-pitched noise out of my speakers, I have to knowck it back a couple of clicks so that I can't hear it.

How do I get rid of it and while I'm there, how do I deal with the ground loop stuff too?

[paulrockliffe]

Sorry, that wasn't the greatest description was it, I was in a rush.....

PC is on the floor, amplifier is on the desk above, it's an analogue connection to the amplifier, 3.5mm jack to twin RCA, I guess the cable is pretty basic. Then the speakers are about a metre above the desk, with decent enough cable running up and along a shelf.

Everything is plugged into the same multiplug and then to a single wall outlet.

[paulrockliffe]

Thanks, that's really helpful and it sounds like something I'll be able to sort to some extent without a load of messing around and hassle.

The issue is primarily when I'm not listening to anything but the amplifier is on, you're right it's drowned out when there's music etc playing, but I tend to have the amplifier on when I'm working whether I'm listening to anything or not and I don't really want to change that.

The secondary issue is that to make it go away I have the amplifier volume turned down, then the computer volume doesn't really go loud enough and the amplifier is behind the monitors out fo the way, so that's irritating.

[paulrockliffe]

megaphone said:

First thing I would try is a decent 3.5mm to phono cable.

Tried that and it's made a big difference, not perfect but quite a lot better. Not sur eif it's good enoguh that I'll forget about it and stop noticing, but it's a step forward.

What should I look at next?

[paulrockliffe]

peterperkins said:

Keep the 3.5-Phono cable as short as possible and don't route it near power supplies or other cables.

So you're saying it shouldn't go through a 2 inch hole at corner of my desk alongside 4 monitor cables and 6 power cables?

I'm not sure I can really move anything to avoid that at the moment, it's too big a job, but I'll get it sorted eventually.

[paulrockliffe]

megaphone said:

Does your amp have an earth on the mains cable? Or just a twin L/N?

I don't know to be honest and it's a sealed plug so I'm not sure I can check very easily. Another one to look at down the line when I have chance.....

[paulrockliffe]

TonyRPH said:

It would seem that the LED brightness controller in the keyboard is radiating interference (it's likely that it's some cheap buck converter or similar).

Do you have a decent quality PSU in your computer?

So is the amplifier left at a fairly high volume setting, and you're controlling the volume from the PC?

This won't be helping.

Does the noise vary with on screen content, or change with mouse movement?

What make & model is the amp you are using? Is it supplied directly from the mains, or does it have an external power brick?

Finally - that you can control the level of noise by adjusting the volume control on the amp suggests the noise is radiated noise being picked up by the cable.

It's not just the keyboard, it was already an issue, the keyboard just made it annoying enough to do something about it. They keyboard isn't a cheap one, but I don't know that that means it doesn't have cheap bits in it.

I've no idea about the PSU in the PC, it all seems like decent stuff but I didn't build it myself and I wouldn't know enough about what is good or bad to really know.

I wouldn't say the amplifier is much beyond 10% volume, but yes I'm controlling the output volume from the PC. The interference doesn't change when I use the PC at all, it's either there or it's not.

Amp is a Cambridge Audio Azur 340A, no external power thingy.

Like I said, it has mainly cleared up with a new cable, but not 100% yet.