Computer Noise Through Speakers

[Kerb26]

I’m using a pair of Dynaudio BM5 Mk1 passive monitors with an Alesis RA-100 power amp.

After buying a new PC and interface, I’m getting computer noise through the speakers. It’s probably because I’m using unbalanced cables, but the RA-100 only has unbalanced inputs.

I suppose my options are:

1. Some new active monitors – probably too expensive.
2. Pseudo-balanced cables at around £50 for the pair.
3. A DI box, but this would colour the sound.
4. New power amp with balanced inputs, but it’s difficult to find a good/affordable 2x100W amp.

Any advice would be appreciated.

[Murray B]

I'm not totally sure that a DI box would colour the sound too much but especially if you go for some of the higher end units - the RA100 manual does specifically mention the possibility of a coloured sound though so I can see why you might be concerned. The fancy DI's might cost just as much as a new amplifier though so a more pragmatic and affordable solution might be the ART DTI reviewed in Sound on Sound a while ago, I have one for live use to protect some of my TRS output stuff from an unwanted Phantom Power accident and I'm perfectly happy with it.

Review is here: https://www.soundonsound.com/reviews/art-dti

I can't promise an uncoloured sound but I'd imagine it would do an ok job - hopefully someone who has used one in a monitoring chain might be able to offer some first hand feedback.

[merlyn]

An isolating transformer would be recommended, like this :

http://orchid-electronics.co.uk/dual_isolator.htm

[Murray B]

An isolating transformer would be recommended, like this :

http://orchid-electronics.co.uk/dual_isolator.htm

I'd highly recommend Orchid - very high quality for low prices - I needed XLR's on my box so got the ART but this should help with the TS - TRS troubles.

And cheaper than the ART box too

[Martin Walker]

Another +1 for the Orchid Dual Isolator to cure this particular problem without compromising your audio quality, and it's an absolute bargain at only £19 per channel!

Martin

[Kerb26]

Is an isolating transformer different to a DI box, and would it be less likely to colour the sound?

[Mike Stranks]

Some confusion here which probably needs clarifying for others reading the thread.

A DI box has a specific purpose which is to covert an unbalanced line-level signal (several hundred millivolts) to a balanced mic level signal (single digit or tens of millivolts). It may or may not have an isolating transformer. It's main use is in live-sound where a keyboard, guitar etc can be connected to the mic input on a mixing desk or mixer-amp.

An isolation transformer takes a line-level signal input and using a 1:1 transformer gives a line-level signal output. Apart from earth/ground isolation the signal should not be affected in any way. It is the earth/ground isolation which deals with hums, burbles etc.

In this instance, a DI box would definitely not be the way to go; it would reduce significantly the signal level being received by the RA100.

[Sam Spoons]

An isolating transformer would be recommended, like this :

http://orchid-electronics.co.uk/dual_isolator.htm

I'd highly recommend Orchid - very high quality for low prices - I needed XLR's on my box so got the ART but this should help with the TS - TRS troubles.

And cheaper than the ART box too

My experience is that John Godsland of Orchid will be happy to build your choice of connectors into any of his boxes (where they will physically fit of course), usually for a minimal upcharge.

[Murray B]

Some confusion here which probably needs clarifying for others reading the thread.

A DI box has a specific purpose which is to covert an unbalanced line-level signal (several hundred millivolts) to a balanced mic level signal (single digit or tens of millivolts). It may or may not have an isolating transformer. It's main use is in live-sound where a keyboard, guitar etc can be connected to the mic input on a mixing desk or mixer-amp.

An isolation transformer takes a line-level signal input and using a 1:1 transformer gives a line-level signal output. Apart from earth/ground isolation the signal should not be affected in any way. It is the earth/ground isolation which deals with hums, burbles etc.

In this instance, a DI box would definitely not be the way to go; it would reduce significantly the signal level being received by the RA100.

My bad, apologies all. Enthusiasm doesn't trump expertise and accuracy of language

[Odysseias]

Hi there...

Are you sure the noise you hear is electronic dirt coming from the PC?

First, check that there are no electrical cables parallel to the audio cables. Sometimes, when organizing cables, we forget to insulate or reduce the magnetic field of electrical power cables.

It is also important to be sure that you use cables of acceptable quality.

Are you using a second display connected via HDMI? Try disconnecting the HDMI cable when you hear the noise and check that when you disconnect, the noise ends. If so, you need an HDMI cable with filters.

When it comes to audio, all components connected to an installation must be of acceptable quality and use filters on the cables.

I had a similar problem. I switched the audio cables, separated the power cables from the audio cables and when I tested it, it was clean sound.

After tidying everything up and organizing my desk, I started the program and bam, again the noise. As I remembered that when I did the test I didn't have the external screen connected, I went to disconnect the HDMI plug and that was when I discovered the origin of the problem. I bought an HDMI cable with filters and I never had electronic noise again.

[Kerb26]

It definitely seems to be computer noise. It gets louder when I load my DAW and louder again when I load a project. I haven’t got a second display connected.

It's sounds like the Orchid Dual Isolator is exactly what I need.

Would I go balanced from the audio interface to the isolator, and unbalanced from the isolator to the power amp? Or do I need to keep both the same ie. unbalanced to and from the isolator?

[ef37a]

Kerb26, You do not mention any audio interface so can I conclude you are using the 3.5mm stereo jack output from the PC to RCA plugs into the amplifier?

Even if you do have an interface my next suggestion is still valid. Using a craft knife remove the outer sleeving of the wires about 50mm back from the RCA plugs. This will expose the screen, now being careful not to cut the inner core, remove all of the 50mm of screen on both wires.

This should stop the ground loop and because you have not introduced any transformers there will be no degradation of the sound quality. There is a possible downside. The absence of the screen could cause pickup of radio interference (RFI) This can almost always be fixed by bridging the screen gap with a low value capacitor od about 1nF (= 1000 picofarads). Best soldered but if beyond you twist and tape.

Our dear Hugh uses the Art isolators and reports virtually no quality loss IIRR?

Actually, now I think about it...IF you are using the PC's sound card the transformers would likely not be the weakest link!

Dave.

[merlyn]

Would I go balanced from the audio interface to the isolator, and unbalanced from the isolator to the power amp? Or do I need to keep both the same ie. unbalanced to and from the isolator?

If you have balanced cables (TRS -- TRS) you can use them between the interface and the isolator, then unbalanced between the isolator and the amp.

If you have unbalanced cables (TS -- TS a.k.a an instrument cable) to hand you can use them from the interface and the isolator will still break the ground path, and get rid of the noise.

[Kerb26]

Thanks to everyone for the advice.