Eliminate background noise from your home audio system

There was a time not so long ago that, if I had my hi-fi turned on but no music playing, I could hear a noise coming through the speakers.

Being somewhat of a perfectionist, I set out on how to fix it and found that there were actually two sources for this noise — a ground loop between my computer and my receiver, and my signal cables picking up noise from my network cables.

After addressing the two problems, my amp is now as quiet as it can be. But if you have noise coming from your speakers, how can you diagnose and fix them?

First up, let’s discuss what’s likely causing it.

So what is a ground loop, anyway?

You know how electricity always moves in circuits from positive to negative, yes? And you also know how electronics have a ‘ground’ path that serves as the return path (effectively the negative) for the electricity flowing through them?

Well, a ground loop is when different pieces of electrical equipment, such as your computer and your A/V receiver, are connected together, but have ‘grounds’ at two different electrical potentials.

Skipping over several lessons’ worth of electrical education, this basically means that you get stray electricity flowing where it isn’t meant to, in order to get to one of the grounds, which can then manifest itself as an aurally unpleasant hum or buzz.

Are ground loops a problem for you?

To see if your system is affected by ground loops, simply turn on your receiver and/or amplifier, and — without music playing —
turn the volume up to above where you would normally set it.

Try changing through all of your inputs. Can you hear a low level hum? Buzzes? Clicks?

Any ‘humming’ around 50Hz (60Hz for those in the US) is most likely caused by a ground loop, while intermittent buzzes and clicks are likely a form of electrical interference.

If you turn your amp up loud enough, you’ll probably hear a constant quiet hiss — that’s just the noise floor of your system and nothing to be concerned about (although, if it does concern you, I sense a budding audiophile within. Let those niggles grow… yes, that’s it. Why should your amp hiss like that? Could it be affecting the music? Perhaps it’s time for an upgrade, hmm? Yes! Yes! That’s it! Climb that hi-fi ladder to unattainable perfection! YEEEEESSSSS!).

…ahem…

So if you have audible noise in your system, let’s run through some simple diagnostics to try to isolate what’s causing it. Only after you’ve identified the problem are you in a position to fix it.


A note for cable TV subscribers

CATV-IsolatorThe signal brought in for your cable TV uses its own ground, so can be responsible for ground loops.

Your cable provider should have installed an isolator when they installed your cable, so look for one either around the set-top box itself, or more likely outside in a little grey box known as a ‘Madison box’.

If you can’t find these, or you suspect that the cable isolator wasn’t installed correctly, call your cable provider and hassle them to install it correctly.

It’s probably worth noting that you can purchase your own cable isolators, but there seems little point when your cable provider should install it for free.


Step 1

Does the noise get louder when you increase the volume? Yes? The problem is occurring before the volume control. If not, it’s occurring after, which means it’s a problem internal to your amp.

Sadly, I can’t help you fix that, so you’re going to have to take your A/V receiver to your friendly local repairman (unless you have an external power amp, in which case, it’s likely the connection between the pre- and power-amps that’s the problem

Step 2

Did the noise start when you added a new piece of equipment? If so, disconnect it.

If it goes away, skip to the ‘Fixing the noise’ section to see what to do about it.

Step 3

If the noise is noticeably louder on one input than it is on the others, then it’s probably the component using that input that is the problem.

Disconnect it and see if it goes away.

If it does, skip to the ‘Fixing the noise’ section.

Step 4

If the above steps didn’t lead to insight, disconnect everything (except your speakers and sub) from your receiver (don’t disconnect the cables from the components and leave them plugged in to the receiver, as this will cause hum itself.

Disconnect them from your receiver, and leave them plugged in to the components) and see if the hum is still there.

Yes? If you have a sub, disconnect its signal cable (at the sub’s end this time). Still there? Move the speaker cables away from all other cables, and if the hum is still there, contact your A/V receiver’s manufacturer for return or repair — there’s a fault in it.

If it went away when disconnecting the sub, it’s your subwoofer; be sure to read the section ‘When digital is not an option’.

Step 5

optical-outNext, start connecting components one-by-one until the hum returns.

NOTE: Don’t plug in components while the amp/receiver is on and the volume is turned up — either turn it off or mute it when connecting/disconnecting cables.

Try connecting each component by itself and see if the hum appears when you turn the volume back up — the most likely components to cause hum are cable TV boxes (including TVs, if the cable box connects to them) and computers, so start with them first, if applicable.

If a hum appears, don’t stop there, keep going through your components and plugging in each one by itself to make sure that it isn’t appearing with other components, too.

If you can’t get the hum to reappear when only individual components are connected, connect all of your components again, and disconnect each one, one at a time and one by one, until it stops.

Find out which of the components (there may be more than one), when disconnected, removes the hum, and jump on over to the next section.

If after following these steps you couldn’t find the component(s) that was causing the hum, then you may find some luck by reading the (in-depth and fairly technical) presentation here which, from page 56, includes a different step-by-step way to diagnose common ‘hum’ and interference problems using ‘dummy’ connectors.

Fixing the noise

There are a few generic tips I’ll get to in a moment that will help you fix any ground loop problems, but first, let’s check if it is indeed a ground loop.

If you’ve found one or more components that were introducing noise into your system, the first thing you should do is separate the signal cables of the problematic component(s) from all the other cables in your set up, and see if the noise stops.

It’s commonplace for all of your cables to be routed behind furniture out of view, but running cables next to each other can cause interference (known as ‘induced noise’) between them.

To reduce this type of noise, keep your cables away from each other (especially power and LAN away from audio), minimise their lengths, be sure to kept them unwound (loops can serve as antennas for RF noise), and if they must cross paths, have them cross at 90 degrees to each other.

Cable-OrganisersPro tip: you can use sticky hooks to lift your signal cables off of the floor and away from the power or LAN cables, saving you from having to find a new path around the furniture.

If separating the signal cables from other cables hasn’t fixed the noise coming through your speakers, then it’s quite likely that the problem is a ground loop, so let’s look at how to fix them.

As a ground loop is caused by there being more than one ‘ground’ in an electrical circuit (keeping in mind that every component attached to your A/V receiver is effectively part of one circuit), then in order to fix it, you need to either remove one of the ‘grounds’, or break the circuit up into separate circuits, each with their own ‘ground’.

Now, when I said removing one of the grounds, I don’t mean pulling the earth plug out of one of your components — removing electrical ground from a component designed to use it will make your equipment a fire hazard at best, and a transport to the next world at worst, should a fault occur.

What I really meant was bring the two grounds’ electrical potentials as close to each other as possible.

The best way to do this is to make sure that all of your hi-fi components (that is, anything that connects to your A/V receiver) are plugged into the same power board, or at least the same electrical circuit. Simple, no?

CoaxToOpticalThis doesn’t guarantee removal of ground loops, however. If after doing this your system is still humming, then it’s time to break up the circuit by electrically isolating the noisy component(s) you identified earlier.

The best way to do this is to use optical S/PDIF connections between each of the identified noisy components and your A/V receiver. These, by design, don’t carry any electrical signal, so serve as a perfect way to keep your components electrically isolated from each other.

Note that coaxial S/PDIF connectors still carry electrical signals, so won’t isolate the component the way that an optical S/PDIF cable will.

If you have an old-school amplifier that doesn’t have optical inputs, consider purchasing a DAC (Digital to Analogue Converter) that has optical inputs. There is a small (very small) risk that the DAC may introduce some ground loops of its own but if you connect it to the same power board, it’s unlikely.

A semi-decent DAC can cost as little as about $100 (from a Chinese manufacturer like HiFiMe), but expect to pay about $300–$500 for entry-level ones from more popular brands, up to several thousand for those buyers that have more money than sense.

DAC technology has really improved over the last few years, so if your components are getting on in years, it may even offer a sonic upgrade, further justifying the cost.
If the noisy component only has coaxial S/PDIF output, and not an optical one, then you can purchase a coaxial to optical converter for about $15 off eBay, which will do the trick nicely, and shouldn’t affect your signal (audiophiles that lose sleep over jitter may disagree, but don’t mind them).

If you’ve simply run out of optical connections on your A/V receiver, try swapping a component over from optical to coaxial so that the known noisy component can use the optical instead. Just make sure that the device you swapped over to coaxial isn’t creating a ground loop now, too.

Alternatively, you could use an optical to coaxial converter (the reverse of the one I mentioned earlier, available for the same $15 on eBay), but as it requires its own power supply, just make sure that it isn’t creating a ground loop, either.


Balanced connectors

If you have a high-end system with balanced audio connectors, use those instead of the standard, unbalanced RCA connectors, as they shouldn’t create ground loops.


When digital is not an option

CheapIsolatorIf an optical connection isn’t a possibility — for example, if the component creating the ground loop is your subwoofer, pre-amplifier or other ‘analogue only’ component, and connecting the devices to the same power board didn’t help or isn’t practical — then you’re going to have to isolate the noisy component(s) from your A/V receiver by using a ground isolator (AKA isolation transformer).

These little devices break the electrical coupling of the two devices, and thus also the ground loop, while still allowing the signal to pass through.

But how? It’s not magic, it’s SCIENCE! (AKA coiled copper.) Now, these are available on eBay or from Jaycar for around $10, but I hesitate to recommend them — a cheap isolation transformer is more likely to degrade your signal than an expensive one.

Sadly, high-quality ones, such as those made by broadcast equipment company Jensen that are designed specifically to maintain your sound quality will cost you in the hundreds of dollars, if you can even find them in Australia.

But hey, at $10, give the cheap one a shot and see if you think it degrades the sound before plonking down on the expensive ones — after all, a slightly degraded sound is probably more pleasant than a constant buzzing, anyway.