Ground noise

[notsloe]

Hi everyone,
So I know from reading that this is very common to get a lot of ground noise from the analog output on a computer.
I've read on here that it can be tested by removing ground from the pc, but this is unsafe and should only be done for troubleshooting.

My question is, would a simple ground loop isolator help with this hum?

Here's a link to one that is popular for car use Pac-Audio.com Product Details | iPod Integration for your car and More by Pac-Audio - Connecting you to the future

I know going digital out is the best fix, I have to use analog for my second room input on my receiver since the second room input on my Onkyo is analog only.

Thanks, Will

[Buckapound]

As far as I know, there are two ways to solve this problem.

One is to use a pair of isolation transformers, Like the Jensen ISO-MAX, which are very high quailty wideband audio line transformers. They work great, but are expensive, at about $150 for a stereo version. If you're patient on eBay you may be able to find one for less. If you know your transformers, you might be able to put one together for a little less, but good line transformers are never cheap.

The other solution I know about would be to use optical digital out to an outboard DAC. I know the general feeling around here is that optical is not ideal, but I'm not sure exactly why. Sounds pretty good to me. WAY better than a load of hum, anyway.

Anybody know if a separate power supply for the sound card would help with this?

Hope this helps.

--Buckapound

[5th element]

A separate power supply wont solve a ground loop. The hum from a ground loop occurs because the ground potential that the computer is at and the ground potential that the device after the computer is at, are slightly different. This causes a current to flow down the interconnect cable and induces hum.

The kind of noise that is typically referred to when PCs are mentioned is high frequency switching noise and cannot be directly heard, but it's presence could interfere with any high speed signal converters that the PC might be connected to and perhaps degrade it's performance by a small amount.

To solve a ground loop, a breaker circuit can be used, such as is described here. I wouldn't want to tamper with the PCs grounding either unless it's absolutely necessary. I'd place the ground breaker in whatever the PC is sending the signal to.

[notsloe]

So are you saying that the line level passive ground loop isolator won't do anything?

I will definitely go the DAC route before I spend any appreciable amount of money to lower the noise on the analog output.
The secondary output on the Onkyo powers a pair of Polk Audio bookshelf speakers in the garage, so it doesn't need to be audiophile grade, just needs to not have a noise floor that rivals the music at low volume.

This is the best option I've found so far For only $39.15 each when QTY 50+ purchased - 4X1 HDMI 1.3b Certified Switcher w/ Toslink & Digital Coaxial Port (Rev.2) w/ 3D support. | Auto & Powered HDMI Switches

It will pass full HDMI and has a simultaneous analog stereo output by way of the built in DAC. With this I wouldn't have to change my audio device on the computer every time I want to hear music in the garage, since windows 7 can't output audio to more than one device at a time.

[5th element]

The passive ground loop isolator will work too. Transformers are known as isolators because there is no electrical connection between the two sides, this prevents the ground loop from forming because there is no ground connection between the PC and the following device.

I can see how opening up the Onkyo and installing a ground breaking circuit may not be what you want to do though so another method might be better.

If you wish to break the ground connection you will need to use an optical link between the computer and the DAC. If your computer has an optical output you can connect it to that device you linked to with a fibre optic cable, then connect the analogue output into the Onkyo. Connecting the device to the computer via coax cable or HDMI will not break the ground connection.

[notsloe]

Though the device is primarily an HDMI switch, it does have a 3.5mm stereo jack output. So wouldn't it have to have a DAC.

[5th element]

Yes it should have a DAC, but if you connect a HDMI or a coax cable from the computer to the switch, the ground connection from the PC will carry on into the switch. The analogue outputs will then also carry that ground connection and into your amplifier allowing the ground current to flow - the problem will not be solved.

To break the ground connection from the PC to the amplifier you need to have some isolation of the ground connection somewhere in the chain. The fibre optic cable would do this, but you'd have to have an optical out on the PC though. The switch would then convert the digital signal into analogue and you're job would be done.

If you don't have a toslink output on the computer you'd need a coax to toslink converter. The trouble here is that you will need to ideally have whatever DAC you choose to use next to the amplifier and to ensure that no ground loops are formed between the DAC and the amplifier you'd need to make sure the DAC is double shielded - most are so this shouldn't be a problem.

This makes those simple isolation transformers sound mighty tempting!

[infinia]

HDMI is using differential signals ie twisted pair AFAIK no decoder DAC chips use any connection to HDMI shields or ground. The switches for HDMI just pass the shield connections.
Most commercial audio gear is class II double insulated ie no third wire plugs.

[notsloe]

So the switch wouldn't passed the noise to the analog output?

[infinia]

Originally Posted by notsloe

So the switch wouldn't passed the noise to the analog output?

probably not within the audio band, since the decoder chip can reject common mode stuff out to video.