NOISE when charging laptop having audio out to PA3X

T3X · Post by **T3X** » Sun Dec 22, 2013 7:25 am

This constant buzz only happen when I plug the charger to the laptop at low battery level.

Does anyone know why and how to fix this proplem?

Thanks

karmathanever · Post by **karmathanever** » Sun Dec 22, 2013 10:31 am

I have this problem with a DC adapter - you could try a new adapter/charger...

Pete

T3X · Post by **T3X** » Sun Dec 22, 2013 11:27 am

I tried that first thing Pete, as I got 2 same laptops with 2 same DC adapters.

It's hard to assume both DC adapters (and/or both laptops) having problems. They are good made and quite new.

When my laptop battery is more than half full, it doesn't make any noise if I plug the charger to it. It seems to happen only at low battery.

Moreover, I'm sure it got nothing to do with windows, media player or anything like that as the same thing happens even when the laptop is shutdown or not powered up.

BillyHank · Post by **BillyHank** » Sun Dec 22, 2013 3:07 pm

I recommend you do not leave your laptop unattended while it is charging if you value your home.

I'm just saying - laptop batteries do not have a very good record.

Thoraldus · Post by **Thoraldus** » Sun Dec 22, 2013 4:18 pm

Here are some possibilities ...

1. You have a AC power ground loop between your keyboard and the laptop when you attach the charger.

2. Your charger design is a switch mode power supply and due to poor design the switching frequency is being coupled into the audio section power bus.

3. Your charger design is a switch mode power supply and due to poor design the switching noise is being coupled into your audio input via the audio cables.

4. Any combination of the above.

T3X · Post by **T3X** » Mon Dec 23, 2013 4:33 am

BillyHank wrote:I recommend you do not leave your laptop unattended while it is charging if you value your home.

I'm just saying - laptop batteries do not have a very good record.

Watching the laptop charging for a few of hours can be very hard. Thanks for your advice anyway.

T3X · Post by **T3X** » Mon Dec 23, 2013 4:43 am

Thoraldus wrote:Here are some possibilities ...

1. You have a AC power ground loop between your keyboard and the laptop when you attach the charger.

2. Your charger design is a switch mode power supply and due to poor design the switching frequency is being coupled into the audio section power bus.

3. Your charger design is a switch mode power supply and due to poor design the switching noise is being coupled into your audio input via the audio cables.
4. Any combination of the above.

It's possible.

You know that there is always specific DC adapter for specific laptop. If I get a new DC adapter, it wouldn't help anything.

Does this mean I have to live the noise, unless I change to a new laptop that comes with a good designed DC adapter?

allrics · Post by **allrics** » Wed Dec 25, 2013 2:27 pm

I have the same issue with my laptop. If you get a 3 prong to 2 prong AC adapter you can now plug your laptop into the wall and the noise will be gone. You can buy them from Home Depot for less than $1.

T3X · Post by **T3X** » Thu Dec 26, 2013 2:12 am

allrics wrote:I have the same issue with my laptop. If you get a 3 prong to 2 prong AC adapter you can now plug your laptop into the wall and the noise will be gone. You can buy them from Home Depot for less than $1.

I cut off the earth prong of the wall plug and it works magic. The noise is gone!

Thank you allrics! What a simple solution!

Thoraldus · Post by **Thoraldus** » Thu Dec 26, 2013 3:27 am

T3X wrote:
allrics wrote:I have the same issue with my laptop. If you get a 3 prong to 2 prong AC adapter you can now plug your laptop into the wall and the noise will be gone. You can buy them from Home Depot for less than $1.

I cut off the earth prong of the wall plug and it works magic. The noise is gone!

Thank you allrics! What a simple solution!

So your problem was #1 above. Ground Loop. It would probably be instructive to learn what possible consequences there are when you remove the safety ground on a device.

AntonySharmman · Post by **AntonySharmman** » Thu Dec 26, 2013 10:52 am

For all of you that have audio interference from laptop , you have to specify the frequency of this noise
in order to help you investigating your problem.
For example with 50-60 Hz hum noise is easy to identify your poor or insufficient ground connections but
other noises over 200 Hz - 15 Khz can be caused under many circumstances except a bad external SM
Power Supply , and could easily caused by your laptop itself !

Laptops use double conversion switching circuits for their power supply , one is the external 15-20 V main switching
mode power supply or battery if portable and the second one ,a powerful switching DC converter unknown to the
majority of you that is called picoPSU which converts single DC voltage and distributes the required
3,3/5/12/-12 V power supply voltages for CPU & motherboard , this component (picoPSU) can really produce a
variety of audible parasitic frequencies if not designed properly and does not follow certain specifications !
This picoPSU participates in battery charging !
Therefore in some cases your laptop itself is your main problem !

calaf · Post by **calaf** » Sat Dec 28, 2013 9:50 pm

Had the same problem with my PA1X. As others have mentioned a ground loop is what I was given to understand the problem was

This was resolved by adding a DI Box to the set up.

Currently I am using an Art Pro Audio stereo passive box.

hotkey · Post by **hotkey** » Sun Dec 29, 2013 9:43 pm

Hello,

I had the same problem . ground loop over earth wire from power socket to DC switch.

I use now power supply with two wires between power socket and DC switch (without earth).

I tried also to cut the ground wire on standard DC supply but I did not like this, because measured potential of DC pins was on cca 110-120V (european power supply 230V AC, 50Hz). and low voltage sources like Line-In ports do not neccessary resist such voltage!

I assume that standard power supplies are making some virtual ground and when the ground wire i s cut then DC potential can fly on the cca half of the AC voltage, so I would not recomend to just cut the wire.

Better to find some two wire power supplies.

Regards,

T3X · Post by **T3X** » Mon Dec 30, 2013 1:38 am

Thoraldus wrote:
So your problem was #1 above. Ground Loop. It would probably be instructive to learn what possible consequences there are when you remove the safety ground on a device.

Yes, you did point that out.

If I plug my laptop charger on top of a pippyback plug power cable which powers my pa3x, would that help anything in terms of safty ground?

T3X · Post by **T3X** » Mon Dec 30, 2013 1:45 am

calaf wrote:Had the same problem with my PA1X. As others have mentioned a ground loop is what I was given to understand the problem was

This was resolved by adding a DI Box to the set up.

Currently I am using an Art Pro Audio stereo passive box.

I don't quite understand how this works but I would try not to use extra gears.