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?

[ribbit]

A bit more detail would help.

Are you connecting your PC via USB port to DAC, and then RCA cables from DAC to amp?

Is the PC powered from the same mains sockets/extension as the amplifier?

[VEX]

What cable routes do you have?

Are they bundled together to look neat?

Traditionally interference can only really happen on the analogue side of a system, digital (so USB's etc) have the ability to reject a lot of interference. So I would start on the analogue cable routes.

V.

[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.

[Lucid_AV]

paulrockliffe said:

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.

It's very unlikely that you have a ground loop issue unless the PC is plugged in to a wall socket several metres away from the amp's wall socket.

It's far more likely that there's a lot of RFI noise from the various switch-mode power supplies and high frequency switching circuitry that is being picked up primarily from the poorly-shielded interconnect and maybe also on the PC's analogue output stage too. Certainly you description of what happens with the keyboard fits the bill.

Unless your amp has a plastic case, then it's metal shell will act like a Faraday cage and isolate the circuits from most of the noise. The speaker wires won't be affected much either. The voltage and current levels required to drive loudspeakers will swamp most SMPSU-generated RFI.

Similarly, the magnetic flux around the driver coils for the tweeters and woofers in your speakers is many times more powerful than the induction voltage caused by RFI.

What this comes back to then is the interconnect cable from the PC to the amp. The shielding sucks.

There are a couple of practical solutions. Your first is a better-shielded interconnect. That's easier said than done though. Only a tiny fractional cable resellers know what types of shielding the cable uses. The ideal thing is a double-layer braided shield.

The alternative is an optical cable from the PC sound card to a DAC place on top of of the amp. This limits the exposure risk as optical is immune to RFI.

[anonymous-user]

Time for copper tape and some ferrites.

Seriously though, try holding the cables , touching boxes, moving the cables around to see if you can affect the level of interference in the first instance. If you can, adjustments to cable layout or distance between boxes may improve matters.

Other that, a clip on low frequency ferrite clipped on cables at various places to see if you can affect the level of noise may yield improvements.

It could you just have 2 boxes that aren't 'happy' together in your system.

[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.

[megaphone]

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

[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?

[megaphone]

Try wrapping the cable in some tin foil, it is picking up electrical interference.

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

Edited by megaphone on Thursday 1st July 06:59

[peterperkins]

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

[OldGermanHeaps]

Ground loop isolator transformer

[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.....

[Lucid_AV]

paulrockliffe said:

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.....

Very likely that the amp is double insulated. There's a symbol for that. Google is your friend. Look up the symbol then check on the back of each piece of gear. You'll have your answer to that.

Keeping the cable run short is good advice where practical, but if its not practical then you need the next solution which is a better-shielded connection lead. This is one of the basic troubleshooting steps. Ferrites and ground-loop isolating transformers etc are going to be a waste of time and money if the foundation work of a properly-shielded connection cable isn't in place.

If you want, I can make you a 3.5mm to stereo RCA lead using the same mini diameter double shielded cable that I use for long subwoofer cable installations. I have customers running on anything up to 15m-long sub cables with the wire concealed around the edge of the room running parallel to the socket ring main and past all the other PSUs in other gear.

Where the problem is RFI being picked up by your current leads then this will solve it. If there's still a problem, then it's a ground loop or a faulty bit of hear, so at least know whether or not you need to spend a chunk of dough on more exotic solutions.
Send me a private message re: the lead.

[TonyRPH]

paulrockliffe said:

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?

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?

paulrockliffe said:

<snip>

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.

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

paulrockliffe said:

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.

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.

[OldGermanHeaps]

https://www.amazon.co.uk/dp/B000NVWB9O/ref=cm_sw_r...
They are a bodge, they are cheating rather than sorting the underlying cause. But they work.
Get one from amazon, if it doesnt fix the problem its a free return.

Edited by OldGermanHeaps on Thursday 1st July 13:45

[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.

[dundarach]

Mine did this, bought a second hand USB Creative Sound card, problem gone.