Don Pearce wrote:
Eiron wrote:
Don Pearce wrote:
Eiron wrote:
Dave Plowman (News) wrote:
In article
,
philcud wrote:
Just started to get an earth loop using my laptop as source connected
to amp.
just starte
get 'cricket' type sounds when the laptop is connected to power lead.
problem goes totally when i half remove the power lead,
gets unlistenable when the power lead is removed and laptop
running on
battery.

only just started happening, any ideas?

Earth loops occur when there are two ground paths at different
potentials.
Usually the screen of the interconnecting cable and mains earths
via the
mains plug. And takes the form of hum. If you are running the
laptop on
batteries with the power supply disconnected totally it can't be an
earth
loop.

Could the problem be that there is no earth in the system
rather than too many?


Never a problem. You don't get hum problems with battery-powered gear.

And what's the amplifier powered by?


Doesn't matter. You only connect to earth for safety.

That's not quite true. You sometimes connect to earth to eliminate hum.
I had a setup that wasn't earthed and when someone approached the microphone
it hummed; when they touched a chassis point it stopped humming.
That wasn't an earth loop but it was capacitative pickup of mains
interference as the ground of all the double-insulated kit was
floating at a hundred volts or so. Earthing the amp cured it.
Modern laptop PSUs have three core mains leads so it probably
doesn't happen on new kit.

--
Eiron.

Eiron wrote:
Don Pearce wrote:
Eiron wrote:
Don Pearce wrote:
Eiron wrote:
Dave Plowman (News) wrote:
In article
,
philcud wrote:
Just started to get an earth loop using my laptop as source
connected
to amp.
just starte
get 'cricket' type sounds when the laptop is connected to power
lead.
problem goes totally when i half remove the power lead,
gets unlistenable when the power lead is removed and laptop
running on
battery.

only just started happening, any ideas?

Earth loops occur when there are two ground paths at different
potentials.
Usually the screen of the interconnecting cable and mains earths
via the
mains plug. And takes the form of hum. If you are running the
laptop on
batteries with the power supply disconnected totally it can't be
an earth
loop.

Could the problem be that there is no earth in the system
rather than too many?


Never a problem. You don't get hum problems with battery-powered gear.

And what's the amplifier powered by?


Doesn't matter. You only connect to earth for safety.

That's not quite true. You sometimes connect to earth to eliminate hum.
I had a setup that wasn't earthed and when someone approached the
microphone
it hummed; when they touched a chassis point it stopped humming.
That wasn't an earth loop but it was capacitative pickup of mains
interference as the ground of all the double-insulated kit was
floating at a hundred volts or so. Earthing the amp cured it.
Modern laptop PSUs have three core mains leads so it probably
doesn't happen on new kit.


That was some other problem, that just happened to be cured by grounding.

d

In article ,
Eiron wrote:
Earth loops occur when there are two ground paths at different
potentials. Usually the screen of the interconnecting cable and mains
earths via the mains plug. And takes the form of hum. If you are
running the laptop on batteries with the power supply disconnected
totally it can't be an earth loop.

Could the problem be that there is no earth in the system
rather than too many?

If there's no ground connection between the two using unbalanced
connection you'll not get any signal either.

--
*If a parsley farmer is sued, can they garnish his wages?

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

In article , Don
Pearce

Doesn't matter. You only connect to earth for safety.

That's not quite true. You sometimes connect to earth to eliminate
hum. I had a setup that wasn't earthed and when someone approached the
microphone it hummed; when they touched a chassis point it stopped
humming. That wasn't an earth loop but it was capacitative pickup of
mains interference as the ground of all the double-insulated kit was
floating at a hundred volts or so. Earthing the amp cured it. Modern
laptop PSUs have three core mains leads so it probably doesn't happen
on new kit.


That was some other problem, that just happened to be cured by grounding.

Depends on what you mean. A problem can arise if a system with no explicit
grounding link has a leakage path though a relatively large impedance that
then generates an 'error' signal injected into a signal-sensitive path.
(e.g. being the coupling between windings of an unscreened PSU transformer,
particularly if the effective impedances for the two polarities on each
side differ.) Depends on the details of the system, etc.

The behaviour can then be as described. Mains hum until the system has a
decent ground - which then provides a lower impedance path for the induced
hum currents, so suppresses the effect.

FWIW Many years ago I spent time working on ultra-sensitive signal
detection systems for astrophysics[1]. Often used in places with lousy
power and dubious grounding. I encountered a large variety of situations
that caused hum. Often in ways which the standard descriptions ignore or
assume won't happen. :-)

Slainte,

Jim

[1] Worst for this were bolometric (heat) detectors whose resistance
changed a tiny amount when warmed by the radiation from a distant galaxy.
Thus needing you to sense minute changes in current or voltage when such an
element was biassed. At least with heterodyne mixers you could do
everything at RF and avoid mains. :-)

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

On Jul 10, 10:31*am, "Dave Plowman (News)"
wrote:
In article ,
* *Eiron wrote:

Earth loops occur when there are two ground paths at different
potentials. Usually the screen of the interconnecting cable and mains
earths via the mains plug. And takes the form of hum. If you are
running the laptop on batteries with the power supply disconnected
totally it can't be an earth loop.
Could the problem be that there is no earth in the system
rather than too many?

If there's no ground connection between the two using unbalanced
connection you'll not get any signal either.

--
*If a parsley farmer is sued, can they garnish his wages?

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

Many thanks for the replies.

The distortion is at its worst when the power supply is disconnected
from the laptop, with the laptop running purely on battery power - the
distortion sounds like an earth problem, but very, very loud, totally
overpowering any signal.

with the power supply attached it has a high pitched 'cricket' type
distortion that changes depending on what the computer is doing (ie if
i load the processor it changes).

lastly, if i 'half' remove the power lead from the laptop, such that
the laptop tells me that it is not receiving any power from the lead,
but the lead is still halfway in the socket (maybe earthing?) there is
no distortion to the signal whatsover.

the laptop is an old audiolab powered by a 'kettle' type lead (3
prong).

hopefully this helps

Eiron wrote:

Don Pearce wrote:

Doesn't matter. You only connect to earth for safety.

That's not quite true. You sometimes connect to earth to eliminate hum.
I had a setup that wasn't earthed and when someone approached the microphone
it hummed; when they touched a chassis point it stopped humming.
That wasn't an earth loop but it was capacitative pickup of mains
interference as the ground of all the double-insulated kit was
floating at a hundred volts or so.

A (design ?) defect.


Modern laptop PSUs have three core mains leads

Nonsense.

so it probably doesn't happen on new kit.

Equally nonsense. The Y cap bridging the live and secondary sides is still there
(for EMC - LOL).

Graham

"Dave Plowman (News)" wrote:

Eiron wrote:
Earth loops occur when there are two ground paths at different
potentials. Usually the screen of the interconnecting cable and mains
earths via the mains plug. And takes the form of hum. If you are
running the laptop on batteries with the power supply disconnected
totally it can't be an earth loop.

Could the problem be that there is no earth in the system
rather than too many?

If there's no ground connection between the two using unbalanced
connection you'll not get any signal either.

The problem is that almost no-one here realises what's inside an SMPS ! AND
probably wouldn't believe it if they knew.

Graham

philcud wrote:

The distortion is at its worst when the power supply is disconnected
from the laptop, with the laptop running purely on battery power - the
distortion sounds like an earth problem, but very, very loud, totally
overpowering any signal.

That suggests a serious degree of ****edness.


with the power supply attached it has a high pitched 'cricket' type
distortion that changes depending on what the computer is doing (ie if
i load the processor it changes).

lastly, if i 'half' remove the power lead from the laptop, such that
the laptop tells me that it is not receiving any power from the lead,
but the lead is still halfway in the socket (maybe earthing?) there is
no distortion to the signal whatsover.

Possibly the crap mini jack has lost its earth connection to the pcb. God I
LOATHE those abortions of connectors.

Graham

"Eeyore" wrote in message
...



Possibly the crap mini jack has lost its earth connection to the pcb.


Sounds the most likely explanation.

God I LOATHE those abortions of connectors.


Join the club!

David.

philcud said:

lastly, if i 'half' remove the power lead from the laptop, such that
the laptop tells me that it is not receiving any power from the lead,
but the lead is still halfway in the socket (maybe earthing?) there is
no distortion to the signal whatsover.

the laptop is an old audiolab powered by a 'kettle' type lead (3
prong).

On the 3 pin IEC plug/socket for safety reasons the earth pin is
longer than the live/neutral so the earth connection is first to
make and last to break for safety reasons.

Are both the lap top and amp plugged into the same ring main or wall
socket?

Is your amplifier earthed?

If it is, have you tried disconnecting the earth?

What happens if you leave the power lead plugged into the laptop and
switch the wall socket off so that the laptop is not connected to
power but is connected to earth?

Have you tried disconnecting the earth on the laptop power lead or is
it a moulded plug?
Which you could cut off and replace with an ordinary plug if you want
to try that.




--
Ken