Has anyone had any problems with using their laptop to play music
through an amp and getting interference/noise in the audio when the AC
power is connected. Seems fairly high frequency...

I have a Toshiba Tecra M5

Thanks!

<Ben.Thoman******.com> wrote in message
news:1161869199.890930.16210@b28g2000cwb.googlegro ups.com...
> Has anyone had any problems with using their laptop to play music
> through an amp and getting interference/noise in the audio when the AC
> power is connected. Seems fairly high frequency...
>

It is in fact noise caused by an 'earth loop'. The clue is that it only
occurs on AC. It is caused because your laptop is earthed and so is your
amplifier. The patch lead provides an earth connection between the laptop
and the amplifier completing the loop. The RF energy in and around the
laptop induces a current in this loop (stay mains fields can do the same
thing). The solution is to run your laptop through a socket strip with the
earth wire disconnected (clearly mark it as such). Run the laptop from this
strip only when it is connected to the amplifier - the earth will be
provided via the amplifier.

I have known earth loops destroy computer equipment if the loop just happens
to be the right length.

"M.I.5¾" <no.one@no.where.NO_SPAM.co.uk> wrote in message
news:4540c81d$1_1@glkas0286.greenlnk.net...
>
> <Ben.Thoman******.com> wrote in message
> news:1161869199.890930.16210@b28g2000cwb.googlegro ups.com...
>> Has anyone had any problems with using their laptop to play music
>> through an amp and getting interference/noise in the audio when the AC
>> power is connected. Seems fairly high frequency...
>>
>
> It is in fact noise caused by an 'earth loop'. The clue is that it only
> occurs on AC. It is caused because your laptop is earthed and so is your
> amplifier. The patch lead provides an earth connection between the laptop
> and the amplifier completing the loop. The RF energy in and around the
> laptop induces a current in this loop (stay mains fields can do the same
> thing). The solution is to run your laptop through a socket strip with
> the earth wire disconnected (clearly mark it as such). Run the laptop
> from this strip only when it is connected to the amplifier - the earth
> will be provided via the amplifier.
>
> I have known earth loops destroy computer equipment if the loop just
> happens to be the right length.
>
This is not my experience with ground loops. The noise generated I have
experienced is low frequency.
The OP's problems sounds more like poor filtering of the high frequency from
the power supply.
Terry

Thanks for that, you were indeed correct - it was a ground loop!

I have 2x power supplies for the laptop (one came with a docking
station) - one is earthed, one is not.

The unearthed one works fine

As per Terry's comments I was thinking the same that it was from the
50Hz mains, but the noise was much higher frequency (which made me
think there was something in the battery charge circuit running at
higher frequency).

Anyway all fixed

On Oct 26, 11:49 pm, "M.I.5¾" <no....@no.where.NO_SPAM.co.uk> wrote:
> <Ben.Tho...******.com> wrote in messagenews:1161869199.890930.16210@b28g2000cwb.go oglegroups.com...
>
> > Has anyone had any problems with using their laptop to play music
> > through an amp and getting interference/noise in the audio when the AC
> > power is connected. Seems fairly high frequency...It is in fact noise caused by an 'earth loop'. The clue is that it only
> occurs on AC. It is caused because your laptop is earthed and so is your
> amplifier. The patch lead provides an earth connection between the laptop
> and the amplifier completing the loop. The RF energy in and around the
> laptop induces a current in this loop (stay mains fields can do the same
> thing). The solution is to run your laptop through a socket strip with the
> earth wire disconnected (clearly mark it as such). Run the laptop from this
> strip only when it is connected to the amplifier - the earth will be
> provided via the amplifier.
>
> I have known earth loops destroy computer equipment if the loop just happens
> to be the right length.

"tc" <terrycassidy@msn.com> wrote in message
news:My70h.37334$P7.9916@edtnps89...
>
> "M.I.5¾" <no.one@no.where.NO_SPAM.co.uk> wrote in message
> news:4540c81d$1_1@glkas0286.greenlnk.net...
>>
>> <Ben.Thoman******.com> wrote in message
>> news:1161869199.890930.16210@b28g2000cwb.googlegro ups.com...
>>> Has anyone had any problems with using their laptop to play music
>>> through an amp and getting interference/noise in the audio when the AC
>>> power is connected. Seems fairly high frequency...
>>>
>>
>> It is in fact noise caused by an 'earth loop'. The clue is that it only
>> occurs on AC. It is caused because your laptop is earthed and so is your
>> amplifier. The patch lead provides an earth connection between the
>> laptop and the amplifier completing the loop. The RF energy in and
>> around the laptop induces a current in this loop (stay mains fields can
>> do the same thing). The solution is to run your laptop through a socket
>> strip with the earth wire disconnected (clearly mark it as such). Run
>> the laptop from this strip only when it is connected to the amplifier -
>> the earth will be provided via the amplifier.
>>
>> I have known earth loops destroy computer equipment if the loop just
>> happens to be the right length.
>>
> This is not my experience with ground loops. The noise generated I have
> experienced is low frequency.
> The OP's problems sounds more like poor filtering of the high frequency
> from the power supply.
> Terry

This depends on where you experienced your earth loop. If you have one on
audio equipment, then generally it will be low frequency noise. But where
there is a computer involved, the noise can be of higher frequency. It is
dependant on the frequencies present near the loop and the geometry of the
loop. The noise is often the interference of one source beating against
another. In fact it is quite possible that the noise can be above audio
frequency (and was the case with the earth loop mentioned that destroyed a
computer - the earth was oscillating at 3 Mhz).

The high frequency in the power supply is above the range of human hearing,
so poor filtering should not make it audible unless the power supply has a
fault that makes it have a parasitic oscillation within that range. But if
it did, you would clearly hear it from the power supply itself.

The symptoms described by the OP are almost certainly an earth loop. I have
experience them several times and breaking one earth always cures it.

<Ben.Thoman******.com> wrote in message
news:1161908077.945393.128500@m73g2000cwd.googlegr oups.com...

Thanks for that, you were indeed correct - it was a ground loop!

I have 2x power supplies for the laptop (one came with a docking
station) - one is earthed, one is not.

The unearthed one works fine

As per Terry's comments I was thinking the same that it was from the
50Hz mains, but the noise was much higher frequency (which made me
think there was something in the battery charge circuit running at
higher frequency).

Anyway all fixed

-------------------

As an additional thought: it is quite possible that one of those core
filters (the type you clamp around the cable) might isolate the interference
without affecting the safety aspects of the earth.