Re: laptop supply needs filtering ?

On Sep 23, 6:55 pm, "mark krawczuk" <krawc...@xxxxxxxxxxx> wrote:
hi, a friend of mine has setup a conference listeneing using VOIP .

he has the pre amp out connected straight up to the laptop .
he has the mains adapter plugged in to the laptop.
but there is a hum coming thru ,, when he disconnects the mains supply for
the laptop , and the laptop runs on its own batteries , the hum goes away
....

would the laptop supply need some sort of filtering ?
thanks,

mark

This is usually because the laptop power supply does not provide an
earth connection and there is significant leakage current.

I'v sometimes found it painfull to have a laptop in my lap while
wearing shorts due to leakage current.

A little bit of 50/60hz current can pass through the capacitance
between
the mains side and the DC side in the power supply.

I have a theory that this is more of a problem in countrys with
230/240volt mains and where the neutral of the mains supply is usually
earthed
at the local substation. You appear to be in australia which has
240volt
mains.

I believe the USA usually has an earthed center tap on the
distribution
transformers that supply houses so the mains only swings 55Volts rms
above/below earth potential compared to the live conductor being 240V
rms
(360v peak) above earth in other systems.

240volt systems are of course vastly superior to 110volt systems in
other
ways such as brownouts being unheard of, fewer electrical fires
because
faults are more likely to trip breakers, fewer distributions
transformers per
household etc.

There are a few approches to the humm problem.
I'd try an isolating transformer because I have a few around and also
because I'd use equipment with balanced audio inputs and ouputs that
is less prone to this sort of problem.

Audio isolating transformers are sometimes known as "DI box's" to
sound engineers.

Earthing the laptop might cure the problem. I'd use a mains plug
with a 1000ohm resistor in it and a D connector to get a connection
to the laptop chassis.

Bob


.

Relevant Pages

  • Re: laptop supply needs filtering ?
    ... he has the mains adapter plugged in to the laptop. ... Either get some properly designed audio gear or run the laptop on batteries. ... rises above mains earth (right now, ...
    (sci.electronics.design)
  • Re: my modest home-recording set-up - advice?
    ... I will try seeing what happens when I'm not using mains power. ... my 15 quid mic so I could use it with less noise. ... >>to WMA-ise some records and tapes, but also to use my stereo microphone ... Does the buzzing depend on whether the laptop is running on batteries ...
    (rec.music.makers.guitar.acoustic)
  • Re: Alternative to conventional wi-fi network?
    ... How much cable do you run before it isn't a wifi net any more? ... I don't want my laptop plugged in *anywhere* directly. ... into a mains network; if you had a room with bad reception due to the ... something like an Airport express might already ...
    (uk.comp.sys.mac)
  • Re: External Hard Drive
    ... up my laptop the only files I keep on it are the image file for my C: ... a full charge and run from the mains. ... Now I have a external HDD connected by USB that was not recognised by ... Does anyone know of any software that will allow me to format the ...
    (alt.comp.hardware.pc-homebuilt)
  • Re: Using 3 Screens with Laptop
    ... Right now, I can only use two screens at a time--either the laptop screen and one LCD, or both LCDs without the laptop screen. ... video connection, and split the image to fit two monitors. ... TripleHead2Go comments - VGA or DVI in, ...
    (microsoft.public.windowsxp.general)