Buzz noise on US-1800 when charging laptop

[rags]

Hello

I had to replace my computer with which I use my US-1800 (the old computer is physically damaged).
Unfortunaltely I have a lot of buzz or hum noise now. I have identified two cases where the noise is particularly bad:
1) when the Laptop's power supply is connected
2) When I connect the external monitor on VGA.
If I hook up one of these cables, the noise level immediately jumps to an unacceptable level.
When the laptop runs on battery with no external display, the sound is fine, but I can't work on that small screen and my battery will not last for more than 2h when I record.

What can I do?

Thanks for your help

 

[Muziekschuur]

I would contact Tascam support. If this is a standard issue they will know why. Personally I have never heard of this issue. But I also have no US-1800...

 

[rags]

I tried to contact them a week ago but didn't get any feedback, that's why I posted here.

Anyways, I dug a little more and found out that the buzz is only generated when my Behringer HA4700 Powerplay Pro-XL Headphone distributor is also plugged in.

I have another headset unit, I will post back here when I know more...

 

[wkrbee]

A case of either radiated RF coming from the switching power supply in the laptop,(don't know if the Beringer has a switcher in it),or a ground loop happening. A 60 Hz buzz is usually a ground loop,higher freq.with a "edge" are usually digital noise from somewhere?, coupling in to the ground of the audio circuitry.

 

[rags]

It's not a low sound, definitely not the 50hz we have in Europe. I would go for a digital noise.

The HA4700 has an internal power supply, its power cord has a ground wire.
The US-1800 comes with an external power supply.

What I have tried:
*Replace the laptop power supply
*change all cables (USB, jacks...)
*Connect either just the US-1800, or the HA4700, or both on a UPS (some APC model)
*Connecting the US-1800 case to that of the HA4700

Anyways, I think the problem is the Behringer unit, not the Tascam, so I'll look for solutions there.

I must say I have been utterly satisfied with this Tascam US-1800. It's a product I would recommend that to any band who wants to record its rehersals multitrack and monitor over headphones.

 

[rags]

So... it seems it was not the Behringer unit genarating the noise. I found out that it is happening also on other headphones units. Actually, it's even there at the headphones out of the Tascam US-1800, except I haden't noticed because it's barely audible. That output volume is way insufficient to hear my own voice next to a drumkit, I'm sure if I could crank it up, it would sound just the same as on the outputs of the Behringer.

So, what I know now: if I take only the tascam and the laptop, and connect USB, everything is fine.
When I connect the laptop power plug, the buzz starts within 2-3 seconds.
This is also the case when I connect the laptop, or the US-1800, or both to a UPS .

What are my options now, if want to avoid using a laptop?
Getting a USB hub with noise filtering capabilities? :S
Using a digital converter at the output of the tascam and enter the headphones distributor from there?

 

[wkrbee]

You have answered your own question .
The laptop charger is either not shielded enough,and is spraying RF,or it is coupling in through the power cord-either the cord going to the laptop, or upstream onto the A/C line and coupling into the US-1800 through it's power cord.Most if not all chargers have a lump,(choke). in the line to block RF.Does the sound change when you move the charger away from the laptop? The simple solution is to use the laptop WITHOUT the charger connected.

 

[rags]

Hello There!

Unplug the charger, that's what I have been doing, but I tell ya, that solution sucked. (computer going to sleep, running out of battery during rehearsals, no more battery on the train in the next morning....)

However, I found a solution:
I got a lucky strike last week when I lost one of the two chargers I owned (I had the noise problem with both).
I went to a computer store where I happen to know the owners and I was able to dig in their "old power supply box". I found 5 compatible ones, so I though I'd take three and check them out.
As a matter of fact, one of them does not induce this noise at all (the two others do).
However, I have no explanation for why this power supply works better than the others. It looks just the same as the other, plain old cheap 19V 3.4A power supplies...

The noise was independent of the physical distance between the charger and the laptop.