Laptops have god-awful switch mode psu's which usually cause problems. Can you run off batteries?

DavidSpearritt wrote: Can you run off batteries?

Yeah, for a limited period. Not the most powerful batteries in this laptop, and I think recording drains a lot of power. But perhaps I should try and see if it gets better if I do so. Anyway, I thought balanced cables were pretty resistant to that kind of stuff...

Hi ellegard,
mightily annoying noise.

I can only do guesses here, but there are probably a few things you can try.

First, I would expect the system to not be grounded. Generally laptop power supply units does not carry ground over to the laptop side. So find something grounded, say a water tap in the kitchen and draw a cable from there. Put the cable to the enclosure of the 410 and see if it makes a difference.

Secondly, the laptop or the power supply unit could be radiating strong radio signals that are somehow picked up. Try moving things around and see what difference it makes.

Maybe you could try with a different firewire cable, you cannot really be sure what helps.

Gunnar

Hi Ellegard,

It sounds like interference from a switching power supply being coupled into the analog front end of the A-D. By chance when you are out in the field, is the Motu interface placed under the PC?
If so, try separating these units to see if it goes away.

Just a thought.

Peter.

Gunnar, thanks for your suggestions. I will try your water tap tip and see if it helps. Moving the FireWire unit around doesn't make any difference - same noise everywhere, and it's regardless if I'm at home, in the conservatory, or at any other remote place. I think I can exclude the firewire cable since the same cable works fine on my home computer.

Peter, I guess you're right about power interference in the AD converter (except this happens to be a M-Audio unit). I usually keep the laptop and the firewire interface apart. I will try, as suggested earlier, to record while running off batteries. If that solves the problem, I might be able to get rid of the noise by buying a longer firewire cable and place the laptop and the M-Audio well apart...

I have not had the 410 apart but I think it uses a switching type of power supply to keep the weight down. The power supply has to provide +/- 15 volts for the opamps plus 48 volts for the phantom. It could be a bad supply. One good way to check is to hold an AM radio tuned off a station close to the 410 and see if it is putting out a lot of hash. If it is the closer you come to it the more noise the radio will make. Not sure about grounding to the water pipe since in some communities there is a rule that you have to have a piece of plastic pipe in between the street feed and the rest of the house so their is no glavantic action happening to the pipes. The other problem could be the computer itself putting out a lot of hash. Again check with an AM radio (some countries call AM Long wave if that makes a difference)

As to battery power. Most computers run off 12 volts DC which can be taken from a motorcycle battery. I made up a small case that has a gell cell motorcycle battery (actually a lawn mower battery) and a connector for my computer. I also have a small charger that goes into the case. I can run my laptop for about 8 hours on the external battery without problems if I am in the field. Maybe this would work for you as well.

Best of luck!

I had the same noise with another, like old vynils. The answer is very simple : unplug the ground of the DC supply of the computer.

To be sure, I asked the builder of my laptop, he told me that there is no problem to do that.

good answer here

http://recording.org/resources/recording-computers.300/

Scott
ADK