Unwanted Noise, Help Please!!

[JFraser]

Hi all,

 

I get really irritating noise from my speakers when my DAC is connected and I don't know what is causing it and how to deal with it. Here is my audio supply chain:

 

Custom built PC >>> Arcam rPac (USB) >>> KRK 10s & KRK VXT6 (x2)

 

I have tried different USB cables (even bought a gold-plated one to see if it would make a difference) but to no avail. It also doesn't make a difference where I place the DAC. I have a feeling it's from the PSU in the PC? Or the motherboard? I'm thinking of buying a USB isolator (something like this http://hifimediy.com/index.php?route=product/product&product_id=122 or this USB-ISO - OLIMEX - USB ISOLATOR, 1000VDC, FOR PC | Farnell UK. Do you think this will solve it?

 

Thanks for all your help.

[Skeptic]

Is it a humming noise?

Are the devices connected to separate outlets?

 

Seems like it's probably a ground loop.

[JFraser]

Is it a humming noise?

Are the devices connected to separate outlets?

 

Seems like it's probably a ground loop.

 

Hi Skeptic, thanks for the message.

 

It's not quite a humming noise, more like a distortion kind of sound which actually seems to change when I click the mouse or change programs etc on the PC. Strangely I can even hear a clock like sound, like a loud second hand on a watch...

 

When you say separate outlets do you mean different power points? I've tried switching the power points/plugs and this doesn't make a difference.

[Paul R]

Hi Skeptic, thanks for the message.

 

It's not quite a humming noise, more like a distortion kind of sound which actually seems to change when I click the mouse or change programs etc on the PC. Strangely I can even hear a clock like sound, like a loud second hand on a watch...

 

When you say separate outlets do you mean different power points? I've tried switching the power points/plugs and this doesn't make a difference.

 

Got bluetooth running anywhere close? Or a cell phone?

-Paul

[One and a half]

To the OP. Avoid computer type USB isolators, a lot of them don't work up to 96kHz, and are NOT USB Audio Class 2 compliant.

 

The KRK 10s has inputs for RCA connections, the VST6 use an XLR/TRS balanced connection. Both speakers require a grounded mains AC supply. Ensure this is complied with.

Your custom computer will also be grounded with an earth wire to comply with local EMC codes.

 

When you connect the DAC with a USB cable and then a RCA cable, you join the signal ground potentials of the computer and the speakers together, and this potential is not the same, that's why you are hearing noises. This will not go away by itself.

 

Since the rDac has only two conductor output (RCA), try the ground lift switch on the woofer. What cables run between the woofer and the VTx6? They should be XLR, not a frankenstein of RCA to XLR/TRS adapters.

 

If the noise is still present, here are some choices.

 

- Buy/borrow an ifiUSB/iPurifier or something similar to provide some real isolation, but causes another problem of the PSU infecting the mains supply. I would be 30% confident of this working.

 

- Replace the Arcam with a DAC that has XLR/TRS outputs that also has a three prong mains AC cord. Run XLR to the woofer. More confidence with this, to 80%.

 

- Replacing USB or the RCA cables will have minimal impact.

 

- Adding ferrites on the USB or RCA cable is hit and miss, our noise is conducted, so direct methods of noise reduction are applicable.

 

- Don't use the volume control on the computer. Keep this at 0db and use a preamp on the output of the DAC.

 

Let's know how you get on.

[sandyk]

To the OP. Avoid computer type USB isolators, a lot of them don't work up to 96kHz, and are NOT USB Audio Class 2 compliant.

 

The KRK 10s has inputs for RCA connections, the VST6 use an XLR/TRS balanced connection. Both speakers require a grounded mains AC supply. Ensure this is complied with.

Your custom computer will also be grounded with an earth wire to comply with local EMC codes.

 

When you connect the DAC with a USB cable and then a RCA cable, you join the signal ground potentials of the computer and the speakers together, and this potential is not the same, that's why you are hearing noises. This will not go away by itself.

 

Since the rDac has only two conductor output (RCA), try the ground lift switch on the woofer. What cables run between the woofer and the VTx6? They should be XLR, not a frankenstein of RCA to XLR/TRS adapters.

 

If the noise is still present, here are some choices.

 

- Buy/borrow an ifiUSB/iPurifier or something similar to provide some real isolation, but causes another problem of the PSU infecting the mains supply. I would be 30% confident of this working.

 

- Replace the Arcam with a DAC that has XLR/TRS outputs that also has a three prong mains AC cord. Run XLR to the woofer. More confidence with this, to 80%.

 

- Replacing USB or the RCA cables will have minimal impact.

 

- Adding ferrites on the USB or RCA cable is hit and miss, our noise is conducted, so direct methods of noise reduction are applicable.

 

- Don't use the volume control on the computer. Keep this at 0db and use a preamp on the output of the DAC.

 

Let's know how you get on.

 

A nice comprehensive answer.

In addition, I would suggest trying the DAC with just headphones, to see if there is another ground loop problem.

It sounds to me like more work may be needed on the PC itself though. Is the PSU new or recycled ?

Alex

[wgscott]

Hi all,

 

I get really irritating noise from my speakers when my DAC is connected and I don't know what is causing it and how to deal with it.

 

Diana Krall

[One and a half]

A nice comprehensive answer.

In addition, I would suggest trying the DAC with just headphones, to see if there is another ground loop problem.

It sounds to me like more work may be needed on the PC itself though. Is the PSU new or recycled ?

Alex

 

In an ideal world, all components within their specs should work together. A toaster, if plugged in will toast bread, that's that it will do until something breaks.

 

Once you delve into the realm of audio that rather simplistic situation defenestrates. Count yourself lucky that the components you buy will work and there's not much noise that you can actually hear. The lower levels where details are found are very often soaked in garbage.

CA has a long way to go as far as 'working' literally thousands of computers, DACs, OS and amplification combinations where audible noise does creep in and for a novice and even experienced CA users come to grief. Each manufacturer, places a sticker to offer compliance with EMC rules, but it means SFA when it's connected to something else. "Our stuff works, must be something YOU are doing wrong" kind of attitude that taints audio in situation like the OP. What can be done about it? Read these pages for clues I suppose, the techniques for curing unwanted noise aren't easy to apply, since cases vary somewhat.

 

The worst thing ever invented for audio was the RCA plug. With computers' efficient noise generators, the RCA plug is inviting drama from the get go.

[sandyk]

The worst thing ever invented for audio was the RCA plug. With computers' efficient noise generators, the RCA plug is inviting drama from the get go.

 

I have lost count of the number of supposedly high quality RCA sockets, and occasionally RCA plugs that I have had to replace in recent years due to loss of correct mating of active and earth sides after a number of plugging in and unplugging cycles.

[wgscott]

Squeeze it with a pair of pliers.

[sandyk]

Squeeze it with a pair of pliers.

 

Been there, done that.

It's the inner of the socket that loses tension too resulting in intermittent connection.

They may have used phosphor bronze years ago which helped to retain tension ?

[JFraser]

Got bluetooth running anywhere close? Or a cell phone?

-Paul

 

No bluetooth but I do have a cell phone. I've moved this to another room however, but still doesn't make a difference

[sandyk]

Have you tried listening directly from the DAC using just headphones yet ?

[JFraser]

To the OP. Avoid computer type USB isolators, a lot of them don't work up to 96kHz, and are NOT USB Audio Class 2 compliant.

 

The KRK 10s has inputs for RCA connections, the VST6 use an XLR/TRS balanced connection. Both speakers require a grounded mains AC supply. Ensure this is complied with.

Your custom computer will also be grounded with an earth wire to comply with local EMC codes.

 

When you connect the DAC with a USB cable and then a RCA cable, you join the signal ground potentials of the computer and the speakers together, and this potential is not the same, that's why you are hearing noises. This will not go away by itself.

 

Since the rDac has only two conductor output (RCA), try the ground lift switch on the woofer. What cables run between the woofer and the VTx6? They should be XLR, not a frankenstein of RCA to XLR/TRS adapters.

 

If the noise is still present, here are some choices.

 

- Buy/borrow an ifiUSB/iPurifier or something similar to provide some real isolation, but causes another problem of the PSU infecting the mains supply. I would be 30% confident of this working.

 

- Replace the Arcam with a DAC that has XLR/TRS outputs that also has a three prong mains AC cord. Run XLR to the woofer. More confidence with this, to 80%.

 

- Replacing USB or the RCA cables will have minimal impact.

 

- Adding ferrites on the USB or RCA cable is hit and miss, our noise is conducted, so direct methods of noise reduction are applicable.

 

- Don't use the volume control on the computer. Keep this at 0db and use a preamp on the output of the DAC.

 

Let's know how you get on.

 

Many thanks for taking the time out to reply with this very helpful post!

 

Just to clarify, my DAC is an rPAC not an rDAC, therefore it is USB powered, it does not have an external power supply. I have already tried the ground lift switch on both the 10s and the VXT6s but this doesn't make a difference. I use XLR to XLR from the 10s to the VXT6s.

 

Interesting what you say about RCA. I had a feeling this might be the problem - I wish the rPAC had balanced outs! I already don't use the volume control on the PC. I have an Unbalanced Emotiva Control Freak connected between the rPAC and the 10s.

 

I don't currently have access to an ifiUSB/iPurifier and/or DAC with balanced outputs so cannot carry out your tests at the moment unfortunately but will try to get my hands on any one of these.

[JFraser]

Have you tried listening directly from the DAC using just headphones yet ?

 

Yes. The headphones work fine.

[JFraser]

A nice comprehensive answer.

In addition, I would suggest trying the DAC with just headphones, to see if there is another ground loop problem.

It sounds to me like more work may be needed on the PC itself though. Is the PSU new or recycled ?

Alex

 

The PSU is a Corsair CX430M. I have used a Lian Li case which is very compact therefore the PSU is very close to the motherboard and everything is quite crampt inside the PC. Do you think this could be the problem? Unfortunately these things are very hard to describe, however, as I said, the sound is not really a humming sound. It's more of a distortion, crackly sound.

[sandyk]

Are you able to post a good quality internal photo of your PC ? It would appear that RF/EMI is getting into the rest of the system via the non isolated USB feed, and this is where it can get very tricky to sort out.

As One and a half has already said, the techniques for curing unwanted noise aren't easy to apply, since cases vary somewhat.

[JFraser]

Are you able to post a good quality internal photo of your PC ? It would appear that RF/EMI is getting into the rest of the system via the non isolated USB feed, and this is where it can get very tricky to sort out.

As One and a half has already said, the techniques for curing unwanted noise aren't easy to apply, since cases vary somewhat.

 

 

You will see that the motherboard is behind the PSU. I can't take a picture behind the PSU...there's no room!

[ecwl]

Keep in mind that the ground loop doesn't have to be from the PC to the speakers. It can be from your monitor to the PC to the speakers or your printer to your PC to your speakers. Or even an external hard drive to your PC to the speakers. So your best bet is to try plugging everything that's interconnected into the same power bar and see if the problem goes away. Alternatively, you may want to unplug everything else from your PC and just address the ground loop between PC and speakers.

[One and a half]

[ATTACH=CONFIG]12306[/ATTACH]

 

You will see that the motherboard is behind the PSU. I can't take a picture behind the PSU...there's no room!

 

Two things you can try.

 

a) Connect a braid cable, say 10mm wide x 0.5 to 1mm thick and connect that (somehow) to the plate where the external connections such as the monitor fit into, there is a special name for it....oh well the brain will think of it tomorrow. It's the silver one. Connect the braid from there to the chassis of the power supply, scrape off as much paint from the power supply as you can to get, to the bare metal. The point is here to make an equi-potential bond between the power supply and the plate, rather than through the circuit of the motherboard and fixing screws.

If you had a scope you could measure a difference between the two metals. Alternatively there maybe a quick connect that you can use on the frame of the PSU where you can attach a braid or cable, but braid is better.

a1) Fit 3mm star washers on the fixing screws on the power supply, these look like a starfish and bite into the metal of the case forming a great bond between the case and the PSU.

 

AND/OR

 

b) I would not normally suggest this.... How good are your neuro-surgery skills? Find a USB cable to the DAC you don't care about, and peel back the cable insulation at the DAC end about 40mm from the plug. Carefully, cut the shield away from the cable, some of them are very fine, others require a bit of effort. Make sure all the strands are peeled back and are clear. Use some insulation tape to hold the wound and keep the shield from coming into contact with anything metallic.

 

The DAC will still work in this case, since the signals inside the cable are differential types, the break in the shield won't be sooo bad. This procedure will stop the noise on the shield being tied to the 0V on the RCA. If this works, then you could confidently purchase an iUSB, since this device has an earth disconnect switch, and you can then use a nice audio grade USB cable, which could be more than the iUSB itself in some cases, but not necessary to go to these extremes.

 

The Control freak is good, keep the player at 0db output and you should be fine. The KRK speakers sound good, it's a shame to put up with the racket.

[One and a half]

Yes. The headphones work fine.

 

Where are they plugged in?

[One and a half]

Hi Skeptic, thanks for the message.

 

It's not quite a humming noise, more like a distortion kind of sound which actually seems to change when I click the mouse or change programs etc on the PC. Strangely I can even hear a clock like sound, like a loud second hand on a watch...

 

When you say separate outlets do you mean different power points? I've tried switching the power points/plugs and this doesn't make a difference.

 

This ticking noise is typical of a switchmode PSU. It could come from the PC or HDD external PSU or even from nothing to do with your PC system!

[Skeptic]

It's not quite a humming noise, more like a distortion kind of sound which actually seems to change when I click the mouse or change programs etc on the PC. Strangely I can even hear a clock like sound, like a loud second hand on a watch...

 

When you say separate outlets do you mean different power points? I've tried switching the power points/plugs and this doesn't make a difference.

Try connecting everything to a single power strip and see if that solves your issue.

 

This is not external interference or due to the components in your system - certainly not due to cables.

It's almost certainly a grounding issue.

[JFraser]

Where are they plugged in?

 

In the headphone out on the DAC/rPAC (which has a built in headphone amplifier).

[JFraser]

Two things you can try.

 

a) Connect a braid cable, say 10mm wide x 0.5 to 1mm thick and connect that (somehow) to the plate where the external connections such as the monitor fit into, there is a special name for it....oh well the brain will think of it tomorrow. It's the silver one. Connect the braid from there to the chassis of the power supply, scrape off as much paint from the power supply as you can to get, to the bare metal. The point is here to make an equi-potential bond between the power supply and the plate, rather than through the circuit of the motherboard and fixing screws.

If you had a scope you could measure a difference between the two metals. Alternatively there maybe a quick connect that you can use on the frame of the PSU where you can attach a braid or cable, but braid is better.

a1) Fit 3mm star washers on the fixing screws on the power supply, these look like a starfish and bite into the metal of the case forming a great bond between the case and the PSU.

 

AND/OR

 

b) I would not normally suggest this.... How good are your neuro-surgery skills? Find a USB cable to the DAC you don't care about, and peel back the cable insulation at the DAC end about 40mm from the plug. Carefully, cut the shield away from the cable, some of them are very fine, others require a bit of effort. Make sure all the strands are peeled back and are clear. Use some insulation tape to hold the wound and keep the shield from coming into contact with anything metallic.

 

The DAC will still work in this case, since the signals inside the cable are differential types, the break in the shield won't be sooo bad. This procedure will stop the noise on the shield being tied to the 0V on the RCA. If this works, then you could confidently purchase an iUSB, since this device has an earth disconnect switch, and you can then use a nice audio grade USB cable, which could be more than the iUSB itself in some cases, but not necessary to go to these extremes.

 

The Control freak is good, keep the player at 0db output and you should be fine. The KRK speakers sound good, it's a shame to put up with the racket.

 

Gosh, I certainly would never have thought to do any of that. If I try them I will let you know the results. Many thanks!