burbeck wrote:
On Wed, 5 Jan 2005 19:29:36 -0000, "Stimpy"
wrote:

OK, I'm asking this on behalf of a friend with no ng access so be
gentle with me if this is a really stupid question!

He's got a Quad 33/303 based system and wants to connect his laptop
to it to play mp3s. He tells me that everything works fine when the
laptop is on battery power but as soon as he plugs in the power
supply, there's a loud humming audible through the stereo speakers.

It's obviously something to do with the presence of the mains power
but what can he do to stop it?

hi yes i agree its a ground loop, good cheap and simple cure is
available from maplins ground loop isolation transformer this is 2
transformers in one (stereo) comes fitted with phono plugs and sockets
on short wires these plugs will have to be changed or adapted to suit
your equipment Maplin code VW43W, cheap enough to give it a try around
£7
regards
bob

Thanks... Message passed on... He's going to give this a try. Might not be
the most elegant solution but if it does the job it'll be fine.

Dave Plowman (News) wrote:

If it's not a wall wart, should be room inside for a larger cap. Be
interesting if the OP could open it up and say what value the
existing one is, along with details of the PS voltage and current.

Apparently it's a separate 'brick' PSU but he's not interested in opening it
up (unless he REALLY has to)

In article ,
Stimpy wrote:
If it's not a wall wart, should be room inside for a larger cap. Be
interesting if the OP could open it up and say what value the
existing one is, along with details of the PS voltage and current.

Apparently it's a separate 'brick' PSU but he's not interested in
opening it up (unless he REALLY has to)

Seems by other posts it's likely to be a simple earth loop. As I said,
this can be checked by measuring for continuity from the earth pin to the
low volt plug with a DVM.

--
*This message has been ROT-13 encrypted twice for extra security *

Dave Plowman London SW
To e-mail, change noise into sound.

burbeck wrote:

hi yes i agree its a ground loop, good cheap and simple cure is
available from maplins ground loop isolation transformer this is 2
transformers in one (stereo) comes fitted with phono plugs and sockets
on short wires these plugs will have to be changed or adapted to suit
your equipment Maplin code VW43W, cheap enough to give it a try around
£7


Sorted! The Maplin's part did the job perfectly... Thanks to Bob for such
spot-on advice

"James Perrett" wrote in message


For some reason newer laptop power supplies are earthed and the earth
is connected to the signal ground of the audio output.

I've noticed a lot of that, too.

If I hadn't recently bought an Acer laptop recently then I would probably
have
thought the same as you, as most older Toshibas, Sonys and Acers that
I've used were double insulated.

Agreed.

I got around it by feeding the output into a decent balanced input and
measured something like 80dB signal to noise ratio - not as good as a
decent 16 bit output should be but OK considering the price of the
components they probably use.

IME, its all in the chips.

"Dave Plowman (News)" wrote in message


Seems by other posts it's likely to be a simple earth loop.

Yes, most likely a simple ground loop, which is often transformed by
overactive mouths and underactive minds into a systematic condemnation of
computer audio.

As I said, this can be checked by measuring for continuity from the earth
pin to
the low volt plug with a DVM.

Agreed.

"burbeck" wrote in message
...
On Wed, 5 Jan 2005 19:29:36 -0000, "Stimpy"
wrote:

OK, I'm asking this on behalf of a friend with no ng access so be gentle
with me if this is a really stupid question!

He's got a Quad 33/303 based system and wants to connect his laptop to it
to
play mp3s. He tells me that everything works fine when the laptop is on
battery power but as soon as he plugs in the power supply, there's a loud
humming audible through the stereo speakers.

It's obviously something to do with the presence of the mains power but
what
can he do to stop it?

hi yes i agree its a ground loop, good cheap and simple cure is
available from maplins ground loop isolation transformer this is 2
transformers in one (stereo) comes fitted with phono plugs and sockets
on short wires these plugs will have to be changed or adapted to suit
your equipment Maplin code VW43W, cheap enough to give it a try around
£7
regards
bob

Thanks for the recommendation. I had a loop hum problem and the Maplin
tranny fixed it. Recommended!

Peter Scott