Notebook, Hum and Ground Lifts

[[email protected]]

I have a Dell Inspiron 9300 and have had issues with a loud hum
entering into my recordings when I power the notebook with AC power.
I initially discovered the problem when using the Presonus Firebox (4
pin to 4 pin firewire). I do not have this issue at all when it is
being powered by batteries. It is also interesting to note that if I
use a DI box and lift the ground on it, the hum goes away. Lately, I
also discovered that if I simpy use the mic/line input on the notebook
and run an output from my mixer, I also get a terrible hum. I have
done some reading on the internet and in general it seems that this is
either caused by a ground loop or from the AC power being converted to
DC power. I can't try my DI box because it only has a XLR output
which doesn't connect to the notebook. One "solution" I read about
that seem to work for about everyone is to use the 3 prong to 2 prong
AC conenctors which removes the ground on the notebook. I don't have
a good understanding of electric and was wondering if someone could
answer some questions for me.

1. Poeple say this is dangerous- is it really dangerous if I am
running a line out from my 3 prong grounded mixer to my now 2 pronged
non-grounded notebook? In my mind it seems that as long as the
notebook is connected to something that is grounded then it shouldn't
be that dangerous.

2. In what situations is removing the ground dangerous?

3. How is using a DI box to "lift" the ground better than removing
the ground from the AC adapter?

Thanks,
Andrew V. Romero

[ChristopheRonald]

buy this.

http://www.audiomidi.com/Hum-X-Ground-Hum-Exterminator-P4803.aspx?CPID=392&AFID=3

you will thank me later.

solves all you problems.

you could figure out how a ground loop works and yada yada yada, and
then you still be mad. just buy this.

[Eeyore]

" wrote:

> I have a Dell Inspiron 9300 and have had issues with a loud hum
> entering into my recordings when I power the notebook with AC power.
> I initially discovered the problem when using the Presonus Firebox (4
> pin to 4 pin firewire). I do not have this issue at all when it is
> being powered by batteries. It is also interesting to note that if I
> use a DI box and lift the ground on it, the hum goes away. Lately, I
> also discovered that if I simpy use the mic/line input on the notebook
> and run an output from my mixer, I also get a terrible hum.

Yes, this is entirely normal.


> I have done some reading on the internet and in general it seems that this is
> either caused by a ground loop or from the AC power being converted to
> DC power.

Kind of a bit of both.

The root cause of this problem is actually the existence of a "Y capacitor" in
the laptop's power supply which is there to meet audio-unrelated regulatory
requirements for 'electromagnetic compatability'. To reduce RF emissions in
fact.


> I can't try my DI box because it only has a XLR output
> which doesn't connect to the notebook.

Get an adaptor lead !


> One "solution" I read about
> that seem to work for about everyone is to use the 3 prong to 2 prong
> AC conenctors which removes the ground on the notebook. I don't have
> a good understanding of electric and was wondering if someone could
> answer some questions for me.

That both (a) won't work and (b) is potentially dangerous.


> 1. Poeple say this is dangerous- is it really dangerous if I am
> running a line out from my 3 prong grounded mixer to my now 2 pronged
> non-grounded notebook? In my mind it seems that as long as the
> notebook is connected to something that is grounded then it shouldn't
> be that dangerous.

Just don't do it. Protective grounding is there for a reason !


> 2. In what situations is removing the ground dangerous?

All situations.


> 3. How is using a DI box to "lift" the ground better than removing
> the ground from the AC adapter?

It breaks the path that matters.

The alternative is to use a non-switchmode power supply for the laptop.

Graham

[Eeyore]

ChristopheRonald wrote:

> buy this.
>
> http://www.audiomidi.com/Hum-X-Ground-Hum-Exterminator-P4803.aspx?CPID=392&AFID=3
>
> you will thank me later.
>
> solves all you problems.

I rather doubt that actually. The problem with laptop power bricks is entirely
something else.

Graham

[Laurence Payne]

On 30 Mar 2007 22:42:02 -0700, "
> wrote:

>3. How is using a DI box to "lift" the ground better than removing
>the ground from the AC adapter?

Because it maintains a robust safety ground connection to the laptop.

[William Sommerwerck]

> Just don't do it. Protective grounding is there for a reason!

The probability of getting a shock from a plastic-cased notebook computer is
nil. Why? Because even if a metal point on the computer had 120V on it,
simply touching it would not produce a shock unless another part of your
body made contact with a grounded conducting surface. (Damp shoes on a
concrete floor _can_ be sufficient, by the way.)

People who claim that lifting the ground is _always_ dangerous know little
about grounding or electricity.

My power amplifiers have a three-pin power cord -- and a ground-lift switch
on the back panel.

One way to resolve this issue is to purchase a small isolation transformer,
and put it between the notebook's power supply and the wall outlet. Look at
the label on the computer's power supply and make sure the transformer can
handle that load.

[Mike Rivers]

On Mar 31, 7:36 am, "William Sommerwerck" >
wrote:

> People who claim that lifting the ground is _always_ dangerous know little
> about grounding or electricity.

Often true.

> My power amplifiers have a three-pin power cord -- and a ground-lift switch
> on the back panel.

That doesn't remove the safety ground, it removes a signal ground.

> One way to resolve this issue is to purchase a small isolation transformer,
> and put it between the notebook's power supply and the wall outlet.

But first, it's best to determine if that's the source of the problem
at all. A safety ground is just that - to protect you from what might
happen if some abnormal condition exists. There's no reason not to
disconnect the safety ground to help analyze the problem. That can be
done with a fifty cent power plug adapter. Just don't stick your
finger inside the computer while you're standing barefoot on a wet
floor and you won't get electrocuted this time.

If that fixes the problem, then an isolation transformer will be a
more permanent and safe solution. The Ebtech Hum-X might also work.
But if lifting the computer ground (or any other ground) doesn't make
the hum go away, neither will a power line isolation transformer. The
problem is caused by something else.

[William Sommerwerck]

> If that fixes the problem, then an isolation transformer will be a
> more permanent and safe solution. The Ebtech Hum-X might also work.
> But if lifting the computer ground (or any other ground) doesn't make
> the hum go away, neither will a power line isolation transformer. The
> problem is caused by something else.

Good point.

[Meindert Sprang]

"William Sommerwerck" > wrote in message
. ..
> > Just don't do it. Protective grounding is there for a reason!
>
> The probability of getting a shock from a plastic-cased notebook computer
is
> nil. Why? Because even if a metal point on the computer had 120V on it,
> simply touching it would not produce a shock unless another part of your
> body made contact with a grounded conducting surface. (Damp shoes on a
> concrete floor _can_ be sufficient, by the way.)

And now I grab the firewire cable, which is already pluggen in the
ungrounded computer and touch the ground sleeve of the firewire plug with
one hand while holding the steel housing of the FireBox which happens to be
grounded via the mixer. Then what?

> People who claim that lifting the ground is _always_ dangerous know little
> about grounding or electricity.

Like I mentioned in an earlier discussion, lifting the protective ground of
a device makes that device floating at half the mains voltage through the
caps of the power filter. Bad idea. Try it. You can feel it tingling in your
fingertips.

> My power amplifiers have a three-pin power cord -- and a ground-lift
switch
> on the back panel.

That switch will NEVER lift the protective ground off the mains. It will
lift the grounds of all audio in- and ouputs off the ground of the mixer.

> One way to resolve this issue is to purchase a small isolation
transformer,
> and put it between the notebook's power supply and the wall outlet. Look
at
> the label on the computer's power supply and make sure the transformer can
> handle that load.

I have a similar setup, with a grounded power brick on my laptop and only
experience this problem when using different AC outlets. I always use a
single power strip or whatever it is called, to feed the mixer, the FireBox
and the Laptop. No problem.

Meindert

[Dave Morrison]

Why not just get a dedicated box to make the connection correctly?:
http://www.zzounds.com/item--WHRPCDI

dave


> wrote in message
ups.com...
>I have a Dell Inspiron 9300 and have had issues with a loud hum
> entering into my recordings when I power the notebook with AC power.
> I initially discovered the problem when using the Presonus Firebox (4
> pin to 4 pin firewire). I do not have this issue at all when it is
> being powered by batteries. It is also interesting to note that if I
> use a DI box and lift the ground on it, the hum goes away. Lately, I
> also discovered that if I simpy use the mic/line input on the notebook
> and run an output from my mixer, I also get a terrible hum. I have
> done some reading on the internet and in general it seems that this is
> either caused by a ground loop or from the AC power being converted to
> DC power. I can't try my DI box because it only has a XLR output
> which doesn't connect to the notebook. One "solution" I read about
> that seem to work for about everyone is to use the 3 prong to 2 prong
> AC conenctors which removes the ground on the notebook. I don't have
> a good understanding of electric and was wondering if someone could
> answer some questions for me.
>
> 1. Poeple say this is dangerous- is it really dangerous if I am
> running a line out from my 3 prong grounded mixer to my now 2 pronged
> non-grounded notebook? In my mind it seems that as long as the
> notebook is connected to something that is grounded then it shouldn't
> be that dangerous.
>
> 2. In what situations is removing the ground dangerous?
>
> 3. How is using a DI box to "lift" the ground better than removing
> the ground from the AC adapter?
>
> Thanks,
> Andrew V. Romero
>

[ChristopheRonald]

so if he buys the product i said it wont work? if not wont work then,
well, what do you suggest he do?

[Richard Crowley]

"Laurence Payne" wrote ...
> " wrote:
>>3. How is using a DI box to "lift" the ground better than removing
>>the ground from the AC adapter?
>
> Because it maintains a robust safety ground connection to the laptop.

There is no "robust safety ground connection" on the
laptop. The only reason for the green-wire ground in
the power cord is so that the manufacturer as some
place to connect those filter capacitors that are supposed
to reduce the horrible hash that comes out of the power
"brick". None of them are very effective IME. I have
seen no difference between ground connected and lifted.

I have yet to see one of those "bricks" where there is
any connection between the green-wire power ground
and the leads that actually go to the computer (or other
equipment). Except maybe one of those ineffectual RF
hash filter capacitors. They are not there for "safety",
they are there to try to reduce the horrible RF hash.

[Richard Crowley]

"Meindert Sprang" wrote ...
> "William Sommerwerck" wrote ...
>> > Just don't do it. Protective grounding is there for a reason!
>>
>> The probability of getting a shock from a plastic-cased notebook
>> computer
> is
>> nil. Why? Because even if a metal point on the computer had 120V on
>> it,
>> simply touching it would not produce a shock unless another part of
>> your
>> body made contact with a grounded conducting surface. (Damp shoes on
>> a
>> concrete floor _can_ be sufficient, by the way.)
>
> And now I grab the firewire cable, which is already pluggen in the
> ungrounded computer and touch the ground sleeve of the firewire plug
> with
> one hand while holding the steel housing of the FireBox which happens
> to be
> grounded via the mixer. Then what?

Then nothing. You have just stated that the computer
is un-grounded. So even if your FireBox has 230VAC
on it, no current will flow because the computer is un-
grounded and provides no return path.

Note that this is also the principle of "double insulated"
products. Note that they have 2-wire power cables.

>> People who claim that lifting the ground is _always_ dangerous know
>> little
>> about grounding or electricity.
>
> Like I mentioned in an earlier discussion, lifting the protective
> ground of
> a device makes that device floating at half the mains voltage through
> the
> caps of the power filter. Bad idea. Try it. You can feel it tingling
> in your
> fingertips.

Thank goodness that only guitar amplifiers have this
goofy (and dangerous) arrangement. Most electrical
equipment is designed more sensibly.

[Laurence Payne]

On Sat, 31 Mar 2007 04:36:26 -0700, "William Sommerwerck"
> wrote:

>My power amplifiers have a three-pin power cord -- and a ground-lift switch
>on the back panel.

Does it lift the POWER ground?

[Eeyore]

Laurence Payne wrote:

> " wrote:
>
> >3. How is using a DI box to "lift" the ground better than removing
> >the ground from the AC adapter?
>
> Because it maintains a robust safety ground connection to the laptop.

Also, removing the ground to the PSU won't solve the problem.

Graham

[Eeyore]

William Sommerwerck wrote:

> > Just don't do it. Protective grounding is there for a reason!
>
> The probability of getting a shock from a plastic-cased notebook computer is
> nil. Why? Because even if a metal point on the computer had 120V on it,
> simply touching it would not produce a shock unless another part of your
> body made contact with a grounded conducting surface. (Damp shoes on a
> concrete floor _can_ be sufficient, by the way.)
>
> People who claim that lifting the ground is _always_ dangerous know little
> about grounding or electricity.

And you're an idiot.

The ground is there for completely different reasons in this kind of case..

Graham

[Eeyore]

ChristopheRonald wrote:

> so if he buys the product i said it wont work? if not wont work then,
> well, what do you suggest he do?

Basically there's very litle you can do.

The problem is endemic with laptops. A 'traditional' non switch-mode PSU will
fix it though.

Graham

[Eeyore]

Soundhaspriority wrote:

> "Eeyore" wrote
> > ChristopheRonald wrote:
> >
> >> buy this.
> http://www.audiomidi.com/Hum-X-Ground-Hum-Exterminator-P4803.aspx?CPID=392&AFID=3
> >>
> >> you will thank me later.
> >>
> >> solves all you problems.
> >
> > I rather doubt that actually. The problem with laptop power bricks is
> > entirely something else.
> >
> It depends upon whether the brick is two-wire or three-wire. If it's
> three-wire, it would definitely help.

Possibly, but it's not reliably the case.

Graham

[Eeyore]

Soundhaspriority wrote:

> He could just buy a two wire power brick from one of the many 3rd party
> suppliers. They come with UL certification, 4KV transformer insulation. 80%
> of laptops these days run on 19V, 3.16 amps.

It may create the same problem though. Quite likely to in fact.

I am actually thinking of creating an audio specific product to address this
using a line frequency toroidal transformer.

Graham

[Eeyore]

Laurence Payne wrote:

> "William Sommerwerck" wrote:
>
> >My power amplifiers have a three-pin power cord -- and a ground-lift switch
> >on the back panel.
>
> Does it lift the POWER ground?

It should *never* lift the connection between the ground pin and the equipment
chassis.

Graham

[Eeyore]

Soundhaspriority wrote:

> "Eeyore" wrote
> > ChristopheRonald wrote:
> >
> >> so if he buys the product i said it wont work? if not wont work then,
> >> well, what do you suggest he do?
> >
> > Basically there's very litle you can do.
> >
> > The problem is endemic with laptops. A 'traditional' non switch-mode PSU
> > will fix it though.
>
> Not at all. A two wire brick will solve the problem. I do it and it works.

You're lucky. It's not a universally reliable solution. It's down to the
internal circuitry of the switcher. In fact the presence or absence of an earth
wire to the PSU is largely incidental.

Only yesterday I had the very problem.

Graham

[Meindert Sprang]

"Richard Crowley" > wrote in message
...
> There is no "robust safety ground connection" on the
> laptop. The only reason for the green-wire ground in
> the power cord is so that the manufacturer as some
> place to connect those filter capacitors that are supposed
> to reduce the horrible hash that comes out of the power
> "brick". None of them are very effective IME. I have
> seen no difference between ground connected and lifted.

That is because the green wire ground is a safety ground, not a ground to
reduce noise. The impedance of the ground wire is the same as the power
wires and will never be a good HF ground.

> I have yet to see one of those "bricks" where there is
> any connection between the green-wire power ground
> and the leads that actually go to the computer (or other
> equipment).

Is that an assumption or a fact? My LiteOn that comes with my Acer has the
safety ground on the AC plug connected to the ground of the DC connector. So
have all other "grounded" bricks I have ever bought.

> Except maybe one of those ineffectual RF
> hash filter capacitors. They are not there for "safety",
> they are there to try to reduce the horrible RF hash.

Again, any wire on a device is too high-impedant to act as a decent RF
ground. The only way to prevent RF interference is to "break" any outgoing
wire on a device for HF, which is done by using a common mode filter.

Meindert

[Meindert Sprang]

"Richard Crowley" > wrote in message
...
> Then nothing. You have just stated that the computer
> is un-grounded. So even if your FireBox has 230VAC
> on it, no current will flow because the computer is un-
> grounded and provides no return path.

There is an AC path through the capacitors of the mains filter.
> Note that this is also the principle of "double insulated"
> products. Note that they have 2-wire power cables.

Ehhr, we were talking about a power brick with ground on the AC plug,
remember?

> Thank goodness that only guitar amplifiers have this
> goofy (and dangerous) arrangement. Most electrical
> equipment is designed more sensibly.

EVERY device with a grounded AC plug has this arrangement. It is mandatory
by regulations.

If you don't believe me, do the test. Take an AC voltmeter and measure the
voltage.

Meindert

[Gdude]

The new power supplies from Dell have only two prongs, no ground
electrode.

I used a 9300 and the sound output was really bad, the internal
computer noise used to seep through. Perhaps the impedance I used was
wrong, but it was rather unusable. I hope you have better luck.

[Richard Crowley]

"Meindert Sprang" wrote ...
> "Richard Crowley" wrote ...
>> Then nothing. You have just stated that the computer
>> is un-grounded. So even if your FireBox has 230VAC
>> on it, no current will flow because the computer is un-
>> grounded and provides no return path.
>
> There is an AC path through the capacitors of the mains filter.
>> Note that this is also the principle of "double insulated"
>> products. Note that they have 2-wire power cables.
>
> Ehhr, we were talking about a power brick with ground on the AC plug,
> remember?

Mine has a 2-prong (ungrounded) power plug.

>> Thank goodness that only guitar amplifiers have this
>> goofy (and dangerous) arrangement. Most electrical
>> equipment is designed more sensibly.
>
> EVERY device with a grounded AC plug has this arrangement. It is
> mandatory
> by regulations.

Regulations are not universal.

> If you don't believe me, do the test. Take an AC voltmeter and measure
> the
> voltage.

I have. Thanks for the tip.

[Richard Crowley]

"Meindert Sprang" wrote ...
> "Richard Crowley" wrote ...
>> There is no "robust safety ground connection" on the
>> laptop. The only reason for the green-wire ground in
>> the power cord is so that the manufacturer as some
>> place to connect those filter capacitors that are supposed
>> to reduce the horrible hash that comes out of the power
>> "brick". None of them are very effective IME. I have
>> seen no difference between ground connected and lifted.
>
> That is because the green wire ground is a safety ground, not a ground
> to
> reduce noise. The impedance of the ground wire is the same as the
> power
> wires and will never be a good HF ground.

"Is that an assumption or a fact?"
(Hint: your theory doesn't agree with my reality.)

>> I have yet to see one of those "bricks" where there is
>> any connection between the green-wire power ground
>> and the leads that actually go to the computer (or other
>> equipment).
>
> Is that an assumption or a fact? My LiteOn that comes with my Acer has
> the
> safety ground on the AC plug connected to the ground of the DC
> connector. So
> have all other "grounded" bricks I have ever bought.

And mine doesn't, so there you are.

[[email protected]]

Thank you for all the ideas so quickly. Although many suggestions
have been offered, it still doesn't seem like there is a consensus on
what the problem is so I would like to answer some of the questions
and give the results of a few tests. I ran some more test and
recorded a small click of the noise I experience when going from the
mixer out to the line/mic input. Please see the wave file at
http://www.u.arizona.edu/~avr/music/ACHum.wav .

With the laptop on battery power, the signal floor is at about -60db
however when I plug the AC power in the floor goes up to between -30
to -20db. If I look at the frequency of the signal, it is mostly in
the 0-50hz range. When looking at a graph of the frequency, it is a
linear graph with most being near the 0hz range (db= -35) and
decreases until it dies out at about 9000hz. There are also some odd
fairly regular clicks that occur about every 0.275 seconds. When
looking at the wave file, the clicks alternate being going up and
down.

The 90 watt "power brick" that feeds the dell inspiron 9300 laptop is
3 pronged. Wrapping the power brick in foil does absolutely nothing.
I tried plugging the power brink into the same surge protector as the
mixer and this had no effect. When I use a 3 prong to 2 prong
adapter, the hum is totally eliminated. I also get the same loud hum
if I attempt to take the headphone out from the notebook and go to a
mixer input.

With this new information, what does everyone think is the cause? To
me, this doesn't seem like a ground loop issue since the hum is not at
60hz. It seems like if the power brick was putting out radio freqs
then the foil should have had some effect. I am still unclear why
using the 3 prong to 2 prong adapter is dangerous with the notebook
especially if some power brings aren't 3 pronged to start with. Do
you think a ground loop isolatator would help with this? Anythink
else you think I should try?

It is amazing that this laptop's audio quality is so poor when plugged
into AC power. How common is this problem for laptops? From my
reading, it seems fairly common...which I still find odd because it
seems like there aren't many solid answers as to what the cause is.

Thanks,
Andrew V. Romero


wrote:
> I have a Dell Inspiron 9300 and have had issues with a loud hum
> entering into my recordings when I power the notebook with AC power.
> I initially discovered the problem when using the Presonus Firebox (4
> pin to 4 pin firewire). I do not have this issue at all when it is
> being powered by batteries. It is also interesting to note that if I
> use a DI box and lift the ground on it, the hum goes away. Lately, I
> also discovered that if I simpy use the mic/line input on the notebook
> and run an output from my mixer, I also get a terrible hum. I have
> done some reading on the internet and in general it seems that this is
> either caused by a ground loop or from the AC power being converted to
> DC power. I can't try my DI box because it only has a XLR output
> which doesn't connect to the notebook. One "solution" I read about
> that seem to work for about everyone is to use the 3 prong to 2 prong
> AC conenctors which removes the ground on the notebook. I don't have
> a good understanding of electric and was wondering if someone could
> answer some questions for me.
>
> 1. Poeple say this is dangerous- is it really dangerous if I am
> running a line out from my 3 prong grounded mixer to my now 2 pronged
> non-grounded notebook? In my mind it seems that as long as the
> notebook is connected to something that is grounded then it shouldn't
> be that dangerous.
>
> 2. In what situations is removing the ground dangerous?
>
> 3. How is using a DI box to "lift" the ground better than removing
> the ground from the AC adapter?
>
> Thanks,
> Andrew V. Romero

[Meindert Sprang]

"Richard Crowley" > wrote in message
...
> "Meindert Sprang" wrote ...
> > That is because the green wire ground is a safety ground, not a ground
> > to
> > reduce noise. The impedance of the ground wire is the same as the
> > power
> > wires and will never be a good HF ground.
>
> "Is that an assumption or a fact?"

That is a fact. Every radio amateur (ham) you ask will tell you that the
safety ground is a poor HF ground.

> > Is that an assumption or a fact? My LiteOn that comes with my Acer has
> > the
> > safety ground on the AC plug connected to the ground of the DC
> > connector. So
> > have all other "grounded" bricks I have ever bought.
>
> And mine doesn't, so there you are.

That is indeed strange, I must admit

Meindert

[Mike Rivers]

On Apr 1, 2:18 am, " >
wrote:

> Please see the wave file http://www.u.arizona.edu/~avr/music/ACHum.wav.

That's definitely a power supply problem. The fundamental frequency is
a bit above 200 Hz (4x the power line frequency) and the "ticking" is
the tipoff.

See what happens when you remove the battery and run it from the AC
supply.

> With the laptop on battery power, the signal floor is at about -60db
> however when I plug the AC power in the floor goes up to between -30
> to -20db. If I look at the frequency of the signal, it is mostly in
> the 0-50hz range. When looking at a graph of the frequency, it is a
> linear graph with most being near the 0hz range (db= -35) and
> decreases until it dies out at about 9000hz.

I don't see that in a spectrum analysis, but most spectrum analyzers
lie in the low frequency range so it's a bit hard to tell what's going
on below 50 Hz. Looks normal to me down there.

> When I use a 3 prong to 2 prong
> adapter, the hum is totally eliminated. I also get the same loud hum
> if I attempt to take the headphone out from the notebook and go to a
> mixer input.

Since the noise is an even multiple of the power line frequency, that
strongly suggests that it's something that the power supply is
introducing. What's happening is that the noise (and I'd describe this
as hum) that the power supply creates is being carried through the
ground and something in the audio system is picking that up and
passing it to a stage that gets it to the output. We call this the
"Pin 1 problem" because on an XLR connector, ground is carried through
pin 1. It's a design flaw in some piece of the system (often difficult
to find the guilty party.

Since the hum is eliminated (how about the "ticking"?) when you remove
the power supply from the safety ground, there's a pretty good chance
that a Hum-X will solve the problem and allow you to keep the safety
ground. I'd suggest that you buy one, try it, and if it doesn't solve
the problem, return it for a refund. It's OK to do that. Some people
have a cultural, moral, or physical bias against that, but there are
some things that you just can't be sure of until you try them in YOUR
system. Make sure your dealer has a friendly return policy. Assuming
you're in Arizona where you posted the sample file, you can get it
from Musician's Friend by mail order if you don't have a convenient
local source, and they'll take it back if you're not satisfied.

The "ticking" sound may be caused by circuitry that monitors the state
of charge of the battery, which is why I suggested trying it with no
battery.

[Meindert Sprang]

"Mike Rivers" > wrote in message
oups.com...
> On Apr 1, 2:18 am, " >
> wrote:
>
> > Please see the wave file http://www.u.arizona.edu/~avr/music/ACHum.wav.
>
> That's definitely a power supply problem. The fundamental frequency is
> a bit above 200 Hz (4x the power line frequency) and the "ticking" is
> the tipoff.

If he's in Arizona, the 200 Hz (210 to be precise) cannot be a multiple of
the power line freuqency as that is 60Hz....

But I agree it comes from some power switcher. It could very well be the
switcher that charges the battery since a switched mode power supply always
runs at several 10's to 100's of kHz.

Meindert

[Mike Rivers]

On Apr 1, 9:12 am, "Meindert Sprang" >
wrote:

> If he's in Arizona, the 200 Hz (210 to be precise) cannot be a multiple of
> the power line freuqency as that is 60Hz....

I wondered about that and attributed the difference to my
unfamiliarity with making measurements with the tools I have. Or maybe
it was 50 Hz but played back at the wrong sample rate. But it
definitely looks like something contributed by the power supply,
though clearly not the switching rate.

[William Sommerwerck]

> I wondered about that and attributed the difference to my
> unfamiliarity with making measurements with the tools I have.
> Or maybe it was 50 Hz but played back at the wrong sample
> rate. But it definitely looks like something contributed by the
> power supply, though clearly not the switching rate.

The switching rate doesn't have to be related to the line frequency.

[[email protected]]

I am in arizona. Both the hum and the clicking are totally eliminated
when I use the 3 to 2 prong connector. I have note done much
frequency analysis and was using acoustica do try and get some of the
information. It is probably not precise enough to get really detailed
information (i.e. hz go in increments of 1000). I don't see why the
frequency of 200hz would indicate a power problem...wouldn't the main
frequency for a power problem be 60hz?

I will try purchasing the Hum X and report back.

Thanks,
Andrew V. Romero

Mike Rivers wrote:
> On Apr 1, 2:18 am, " >
> wrote:
>
> > Please see the wave file http://www.u.arizona.edu/~avr/music/ACHum.wav.
>
> That's definitely a power supply problem. The fundamental frequency is
> a bit above 200 Hz (4x the power line frequency) and the "ticking" is
> the tipoff.
>
> See what happens when you remove the battery and run it from the AC
> supply.
>
> > With the laptop on battery power, the signal floor is at about -60db
> > however when I plug the AC power in the floor goes up to between -30
> > to -20db. If I look at the frequency of the signal, it is mostly in
> > the 0-50hz range. When looking at a graph of the frequency, it is a
> > linear graph with most being near the 0hz range (db= -35) and
> > decreases until it dies out at about 9000hz.
>
> I don't see that in a spectrum analysis, but most spectrum analyzers
> lie in the low frequency range so it's a bit hard to tell what's going
> on below 50 Hz. Looks normal to me down there.
>
> > When I use a 3 prong to 2 prong
> > adapter, the hum is totally eliminated. I also get the same loud hum
> > if I attempt to take the headphone out from the notebook and go to a
> > mixer input.
>
> Since the noise is an even multiple of the power line frequency, that
> strongly suggests that it's something that the power supply is
> introducing. What's happening is that the noise (and I'd describe this
> as hum) that the power supply creates is being carried through the
> ground and something in the audio system is picking that up and
> passing it to a stage that gets it to the output. We call this the
> "Pin 1 problem" because on an XLR connector, ground is carried through
> pin 1. It's a design flaw in some piece of the system (often difficult
> to find the guilty party.
>
> Since the hum is eliminated (how about the "ticking"?) when you remove
> the power supply from the safety ground, there's a pretty good chance
> that a Hum-X will solve the problem and allow you to keep the safety
> ground. I'd suggest that you buy one, try it, and if it doesn't solve
> the problem, return it for a refund. It's OK to do that. Some people
> have a cultural, moral, or physical bias against that, but there are
> some things that you just can't be sure of until you try them in YOUR
> system. Make sure your dealer has a friendly return policy. Assuming
> you're in Arizona where you posted the sample file, you can get it
> from Musician's Friend by mail order if you don't have a convenient
> local source, and they'll take it back if you're not satisfied.
>
> The "ticking" sound may be caused by circuitry that monitors the state
> of charge of the battery, which is why I suggested trying it with no
> battery.

[Mike Rivers]

On Apr 1, 11:17 am, " >
wrote:

> I am in arizona. Both the hum and the clicking are totally eliminated
> when I use the 3 to 2 prong connector.

That's a sure sign of the Pin 1 problem, probably both with the power
supply and computer or Firebox, or all. But all you need to do is
eliminate one of the problems (by disconnecting the power supply
ground from the computer ground) and you'll fix the symptom - until
you have to connect something else up and the problem pops up
elsewhere.

> I don't see why the
> frequency of 200hz would indicate a power problem...wouldn't the main
> frequency for a power problem be 60hz?

Generally power supply hum and buzz is most prevalent at a harmonic of
the fundamental frequency, but it's more often 120 or 180 Hz (2nd and
3rd harmonics) than at 240 Hz. So it's possible that this frequency is
something generated within the power supply, perhaps having to do with
battery charging. That's why I suggested removing the battery to see
if the noise went away.

Laptop computer power supplies are notorious for creating odd noises
in audio system. You probably could operate without the battery (or on
battery, without the power supply connected) if removing the battery
solves the problem. In once instance you'd have power from AC (though
you'd lose the backup security if you lost power) and in the other
instance you wouldn't have power so you wouldn't need the power
supply.

I would be curious to know if the Hum-X fixes the problem, though.
I've been thinking of writing an article about sources of hum and
gadgets you can buy to fix the problems. I don't have anything bad
enough here to test the Hum-X with, though it certainly has its share
of supporters.

I think (don't quote me on this since I've never taken one apart or
even done any measurements on it) that it has two diodes wired back-to-
back in series with the safety ground. That will pass all the current
it need in order to keep you from getting electrocuted if the hot side
of the line should short to something you can touch while you're
grounded, but will be like lifting the safety ground pin with an
adapter when it's not needed to save a life. It's CE approved, so it's
gotta be safe.

[Eeyore]

Gdude wrote:

> The new power supplies from Dell have only two prongs, no ground
> electrode.

Irrelevant to the issue.

Graham

[Eeyore]

Richard Crowley wrote:

> > EVERY device with a grounded AC plug has this arrangement. It is
> > mandatory by regulations.

What arrangement


> Regulations are not universal.

Yes they are actually these days, for all practical purposes.

Graham

[Eeyore]

Richard Crowley wrote:

> "Meindert Sprang" wrote ...
>
> >> I have yet to see one of those "bricks" where there is
> >> any connection between the green-wire power ground
> >> and the leads that actually go to the computer (or other
> >> equipment).
> >
> > Is that an assumption or a fact? My LiteOn that comes with my Acer has
> > the safety ground on the AC plug connected to the ground of the DC
> > connector. So have all other "grounded" bricks I have ever bought.
>
> And mine doesn't, so there you are.

Either way it's completely irrelevant.

It's *NOT* a typical 'ground loop' problem at all.

It's a *LEAKAGE CURRENT* problem from certain RF suppression capacitors in the
switchmode PSU that link the mains input to the secondary circuit.

Graham

[Eeyore]

" wrote:

> Thank you for all the ideas so quickly. Although many suggestions
> have been offered, it still doesn't seem like there is a consensus on
> what the problem is

I'm actually the only one to give you the correct answer but few self-appointed
'experts' here even understand the actual issue because, quite simply, it
requires design experience and insight to understand a very non-intuitive issue.

Graham

[Eeyore]

Meindert Sprang wrote:

> "Richard Crowley" wrote
> > "Meindert Sprang" wrote ...
> > > That is because the green wire ground is a safety ground, not a ground
> > > to
> > > reduce noise. The impedance of the ground wire is the same as the
> > > power
> > > wires and will never be a good HF ground.
> >
> > "Is that an assumption or a fact?"
>
> That is a fact. Every radio amateur (ham) you ask will tell you that the
> safety ground is a poor HF ground.

You are totally correct. In fact at RF the 'ground wire' will measure about 50
ohms.

Graham

[Eeyore]

Meindert Sprang wrote:

> But I agree it comes from some power switcher. It could very well be the
> switcher that charges the battery since a switched mode power supply always
> runs at several 10's to 100's of kHz.

It comes from a 'Y cap', typically 2200pF, that links the rectified mains
voltage to the secondary circuit.

Graham

[Eeyore]

Mike Rivers wrote:

> Generally power supply hum and buzz is most prevalent at a harmonic of
> the fundamental frequency, but it's more often 120 or 180 Hz (2nd and
> 3rd harmonics) than at 240 Hz.

Not with switching supplies.

2nd harmonic is typical power supply ripple contribution amd 3rd harmonic is
'hum' as a result of stray field from the line frequency transformer.

Neither appear for those reasons with a switchmode supply.

Graham

[Eeyore]

William Sommerwerck wrote:

> > I wondered about that and attributed the difference to my
> > unfamiliarity with making measurements with the tools I have.
> > Or maybe it was 50 Hz but played back at the wrong sample
> > rate. But it definitely looks like something contributed by the
> > power supply, though clearly not the switching rate.
>
> The switching rate doesn't have to be related to the line frequency.

It hardly ever is.

Graham

[Eeyore]

" wrote:

> I don't see why the frequency of 200hz would indicate a power problem...

Such problems don't fall into the " I don't see " category based on supposed
'common sense'. Unless you're an electronics designer you assuredly *won't see*.
It is *not* a simple to understand intuitive issue.


> wouldn't the main frequency for a power problem be 60hz?

Not with a switchmode supply.

Graham

[Meindert Sprang]

"Eeyore" > wrote in message
...
>
>
> Meindert Sprang wrote:
>
> > But I agree it comes from some power switcher. It could very well be the
> > switcher that charges the battery since a switched mode power supply
always
> > runs at several 10's to 100's of kHz.
>
> It comes from a 'Y cap', typically 2200pF, that links the rectified mains
> voltage to the secondary circuit.

Graham,

Could it be interference of a possible PFC circuit before the rectifier?
I'm a bit puzzled about the frequency, which appeared to be 210 Hz when
measuring the OP's file in Audacity.

Meindert

[[email protected]]

Thank you for your insight. Next time I will have to ask for resumes
before reading everyone's answers:)

With all kidding aside, thanks for the answers everyone. Hopefully
this is a fairly complete thread on the issue. I ordered two Hum X's
from audiomidi.com and they should be here by wednesday. It will be
interesting to see if they work. Of course, if they do...the next
question is how/why? These seem like odd devices because they seem to
solve problems like this but I haven't read much about the why or
how. When I first read about it, it seemed more like a scam...you
know the this filters all your power and gives you clean, pure power,
run your audio thru this and it will be flawless, etc etc.

-Andrew V. Romero

Eeyore wrote:
> " wrote:
>
> > Thank you for all the ideas so quickly. Although many suggestions
> > have been offered, it still doesn't seem like there is a consensus on
> > what the problem is
>
> I'm actually the only one to give you the correct answer but few self-appointed
> 'experts' here even understand the actual issue because, quite simply, it
> requires design experience and insight to understand a very non-intuitive issue.
>
> Graham

[Eeyore]

Meindert Sprang wrote:

> "Eeyore" wrote
> > Meindert Sprang wrote:
> >
> > > But I agree it comes from some power switcher. It could very well be the
> > > switcher that charges the battery since a switched mode power supply
> >> always runs at several 10's to 100's of kHz.
> >
> > It comes from a 'Y cap', typically 2200pF, that links the rectified mains
> > voltage to the secondary circuit.
>
> Could it be interference of a possible PFC circuit before the rectifier?

No. Active PFC operates in the hundreds of kHz.


> I'm a bit puzzled about the frequency, which appeared to be 210 Hz when
> measuring the OP's file in Audacity.

That's curious. I haven't had time to listen to it yet.

Graham

[Eeyore]

" wrote:

> Thank you for your insight. Next time I will have to ask for resumes
> before reading everyone's answers:)
>
> With all kidding aside, thanks for the answers everyone. Hopefully
> this is a fairly complete thread on the issue. I ordered two Hum X's
> from audiomidi.com and they should be here by wednesday. It will be
> interesting to see if they work. Of course, if they do...the next
> question is how/why?

It's simple. It's a matter of dealing (in one way or another) with the leakage current
from a 2200pF (typically - might be as low as 1000pF) capacitor.

Graham

[Mike Rivers]

On Apr 2, 8:17 pm, Eeyore >
wrote:

> 2nd harmonic is typical power supply ripple contribution amd 3rd harmonic is
> 'hum' as a result of stray field from the line frequency transformer.
>
> Neither appear for those reasons with a switchmode supply.

Then how do you explain the 200+ Hz in his "hum?"

I suggest that he start sending his system, complete, including a UPS
or FedEx account number, around to all of us so we can take a closer
look. We should have an answer in a couple of months, if it still
works at all after that.

[Mike Rivers]

On Apr 2, 8:11 pm, Eeyore >
wrote:

> I'm actually the only one to give you the correct answer

This thread is getting too long. Would you mind reviewing your answer
(and explanation) for those of us who are eagerly awaiting the
confirmation of your diagnosis?

[Mike Rivers]

On Apr 3, 3:13 am, Eeyore >
wrote:

> It's simple. It's a matter of dealing (in one way or another) with the leakage current
> from a 2200pF (typically - might be as low as 1000pF) capacitor.

What capacitor? And if the capacitor is leaking, why not replace it
with one that isn't defective?

[No Name]

Eeyore > wrote:
>
>
> ChristopheRonald wrote:
>
>> so if he buys the product i said it wont work? if not wont work then,
>> well, what do you suggest he do?
>
> Basically there's very litle you can do.
>
> The problem is endemic with laptops. A 'traditional' non switch-mode PSU will
> fix it though.
>
> Graham

....and they aren't even especially expensive.

--
Aaron

[[email protected]]

I purchased two Hum X from audioMIDI.com and they work really well!
They totally eliminiate both the hum and the clicks. I can no longer
hear any difference between running the notebook off the batteries or
AC power. My notebook is now actually useful for recording when
powered by AC power. I am still not exactly clear why these work or
what it is that they do, but they are worth the $50 each for me.

I also ran another test and used AC power without the Hum X. I then
removed the battery, and clicks did go away. The hum was still just
as loud, but the clicks were totally eliminated so your guess about
the clicks being related to the battery charging must be correct. So
if the clicks have to do with the battery charging, why does running
the AC power thru the Hum X eliminate the clicks...the battery is
still being charged so I would have expected the clicks to remain.
Quite mysterious... I also found that if I use a DI box and lift the
ground signal between the notebook and the other piece of AC powered
music equipement (i.e. keyboard, mixer, etc), that the hum and clicks
are totally eliminated, however just using the Hum X is much easier
than trying to connect everything thru a DI box.

You know what is funny? Check out the second message in this
thread...should have listened to Christopher earlier :) I still think
this may drive me crazy, but at least I know the Hum Xs magically
solve the problem

Thanks for your help everyone. This newsgroup is great for odd
questions like this!
Andrew V. Romero

wrote:
> Thank you for your insight. Next time I will have to ask for resumes
> before reading everyone's answers:)
>
> With all kidding aside, thanks for the answers everyone. Hopefully
> this is a fairly complete thread on the issue. I ordered two Hum X's
> from audiomidi.com and they should be here by wednesday. It will be
> interesting to see if they work. Of course, if they do...the next
> question is how/why? These seem like odd devices because they seem to
> solve problems like this but I haven't read much about the why or
> how. When I first read about it, it seemed more like a scam...you
> know the this filters all your power and gives you clean, pure power,
> run your audio thru this and it will be flawless, etc etc.
>
> -Andrew V. Romero
>
> Eeyore wrote:
> > " wrote:
> >
> > > Thank you for all the ideas so quickly. Although many suggestions
> > > have been offered, it still doesn't seem like there is a consensus on
> > > what the problem is
> >
> > I'm actually the only one to give you the correct answer but few self-appointed
> > 'experts' here even understand the actual issue because, quite simply, it
> > requires design experience and insight to understand a very non-intuitive issue.
> >
> > Graham

[Mike Rivers]

On Apr 7, 3:13 am, " >
wrote:
> I purchased two Hum X from audioMIDI.com and they work really well!
> They totally eliminiate both the hum and the clicks.

> I also ran another test and used AC power without the Hum X. I then
> removed the battery, and clicks did go away. The hum was still just
> as loud, but the clicks were totally eliminated so your guess about
> the clicks being related to the battery charging must be correct. So
> if the clicks have to do with the battery charging, why does running
> the AC power thru the Hum X eliminate the clicks...

Because the clicks are still there, but they're being carried to the
computer through the ground. The Hum-X disconnects the computer ground
from the rest of the world until it's necessary to connect it. While I
wouldn't have thought about it, it's not unreasonable for battery
charger clicks to affect the ground potential since they're probably a
result of large but short duration current surges.

Anyway, I'm glad to hear that you found a workable solution that
doesn't compromise your personal safety.

[Eeyore]

Mike Rivers wrote:

> Eeyore wrote:
>
> > It's simple. It's a matter of dealing (in one way or another) with the leakage current
> > from a 2200pF (typically - might be as low as 1000pF) capacitor.
>
> What capacitor?

The 'Y cap' that bumps unwanted HF energy back from the secondary side to the primary
reservoir cap. Most SMPS designs have it (whether 2 or 3 wire).


> And if the capacitor is leaking, why not replace it with one that isn't defective?

It's not defective. It's doing what it's meant to do (for EMC).

Graham

[Mike Rivers]

On Apr 8, 3:37 pm, Eeyore >
wrote:

> > What capacitor?
>
> The 'Y cap' that bumps unwanted HF energy back from the secondary side to the primary
> reservoir cap. Most SMPS designs have it (whether 2 or 3 wire).
>
> > And if the capacitor is leaking, why not replace it with one that isn't defective?
>
> It's not defective. It's doing what it's meant to do (for EMC).

I'm afraid I've lost the threa here. I had to think hard before I
figured out what SMPS meant. I thought we were talking about a hum
problem, not an EMI problem, but it's easy to get derailed when you
know something.

I'm not familiar with the design of switching mode power supplies. I
just replace 'em when they stop working, so I don't know what the "Y
cap" is and why there would be unwanted energy at the secondary and
that you'd want to couple back to the primary. However, if it causes a
problem with the audio, it's an inappropriately applied design.

[Richard Crowley]

"Mike Rivers" wrote ...
> I'm afraid I've lost the threa here. I had to think hard
>before I figured out what SMPS meant. I thought we
> were talking about a hum problem, not an EMI problem,
> but it's easy to get derailed when you know something.

Many people use "hum" as a generic term for unwanted
noise. It doesn't necessarily mean something related to
power mains frequency.

> I'm not familiar with the design of switching mode
> power supplies.

SMPS (switch-mode power supplies) basically work by
rectifying the raw mains power (like old AC-DC radios)
and then creating a high-frequency AC out of it to feed
through a smaller (and cheaper) ferrite transformer.
Alas, this high-frequency operation directly from the
mains input if often the source of EMI as designs are
rarely optimized for minimal interference.

> I just replace 'em when they stop working, so I don't
> know what the "Y cap" is and why there would be
> unwanted energy at the secondary and that you'd
> want to couple back to the primary. However, if it
> causes a problem with the audio, it's an inappropriately
> applied design.

Alas, SMPS are getting cheaper than traditional old
analog designs with heavy iron transformers, so we are
seeing more and more "inappropriately applied" designs.
:-(

Some enterprising person will start a "retro PS" business
replacing these "inappropriately applied" SMPS with the
old-fashioned heavy-iron traditional kind. Just think how
much smoother the audio will sound with all that heavy
iron in the power supply! :-)

[Mike Rivers]

On Apr 8, 4:10 pm, "Richard Crowley" > wrote:

> Many people use "hum" as a generic term for unwanted
> noise. It doesn't necessarily mean something related to
> power mains frequency.

Yes, I know, and that often gets discussions off on the wrong track
when someone wants to know what to do about "hum" and it's really
something else entirely.

> SMPS (switch-mode power supplies) basically work by
> rectifying the raw mains power (like old AC-DC radios)
> and then creating a high-frequency AC out of it to feed
> through a smaller (and cheaper) ferrite transformer.
> Alas, this high-frequency operation directly from the
> mains input if often the source of EMI as designs are
> rarely optimized for minimal interference.

I know how they work, I just don't know the tricks. Between FCC and CE
standards and regulations, they have to be buttoned up and filtered
well enough so that they don't interfere with common household things
like radios, televisions, and telephones, but I doubt that they're
tested to be safe around high gain, low noise audio equipment. It
would be smart of the audio manufacturers to make their gear well
enough shielded and filtered so that noise that gets out of "approved"
power supplies wouldn't bother the audio, but some are better than
others.

> Alas, SMPS are getting cheaper than traditional old
> analog designs with heavy iron transformers, so we are
> seeing more and more "inappropriately applied" designs.
> :-(

They always have been cheaper than analog regulated, line-frequency
designs on a watts-per-dollar basis. That's at least one reason why
they were invented (the other being weight). But there are probably
better and worse ways of making a switching power supply.

> Some enterprising person will start a "retro PS" business
> replacing these "inappropriately applied" SMPS with the
> old-fashioned heavy-iron traditional kind. Just think how
> much smoother the audio will sound with all that heavy
> iron in the power supply! :-)

It would be a mighty hard sell. Have you priced analog power supplies
lately? You'd expect to find one (and you do) in a $1,000 mic preamp.
And you probably would find one in a $5,000 computer that was purpose-
built for audio applications. Then someone would come along and ruin
it all by hanging his cell phone on the mic stand.

[Eeyore]

Mike Rivers wrote:

> Eeyore wrote:
> > Mike Rivers wrote:
> >
> > > What capacitor?
> >
> > The 'Y cap' that bumps unwanted HF energy back from the secondary side to the > primary
> reservoir cap. Most SMPS designs have it (whether 2 or 3 wire).
> >
> > > And if the capacitor is leaking, why not replace it with one that isn't defective?
> >
> > It's not defective. It's doing what it's meant to do (for EMC).
>
> I'm afraid I've lost the threa here. I had to think hard before I
> figured out what SMPS meant. I thought we were talking about a hum
> problem,

We are.

> not an EMI problem, but it's easy to get derailed when you
> know something.
>
> I'm not familiar with the design of switching mode power supplies. I
> just replace 'em when they stop working, so I don't know what the "Y
> cap" is and why there would be unwanted energy at the secondary

Due to the high frequency switching of the SMPS along with the various consequences of
practical transformer design.


> and that you'd want to couple back to the primary.

To meet the EMC compliance specs.


> However, if it causes a problem with the audio, it's an inappropriately applied design.

It causes an AC line frequency (plus harmonics) 'leakage current' from the AC mains into
the secondary circuits. That's where your hum comes from when the laptop is connected to
grounded audio equipment as the leakage current finds a path to ground through the audio
interface.

Graham

[Eeyore]

Mike Rivers wrote:

> On Apr 8, 4:10 pm, "Richard Crowley" > wrote:
>
> > Many people use "hum" as a generic term for unwanted
> > noise. It doesn't necessarily mean something related to
> > power mains frequency.
>
> Yes, I know, and that often gets discussions off on the wrong track
> when someone wants to know what to do about "hum" and it's really
> something else entirely.

This IS hum I'm referring to.

Graham

[Eeyore]

Mike Rivers wrote:

> I know how they work, I just don't know the tricks. Between FCC and CE
> standards and regulations, they have to be buttoned up and filtered
> well enough so that they don't interfere with common household things
> like radios, televisions, and telephones, but I doubt that they're
> tested to be safe around high gain, low noise audio equipment.

That's not a requirement as such in the standards.


> It would be smart of the audio manufacturers to make their gear well
> enough shielded and filtered so that noise that gets out of "approved"
> power supplies wouldn't bother the audio, but some are better than
> others.

The answer here would be to make 'audio grade' laptop power supplies. I'm
considering it. You can't blame external audio kit for the leakage current from
the laptop.

Graham

[Mike Rivers]

On Apr 9, 1:28 pm, Eeyore >
wrote:

> > > The 'Y cap' that bumps unwanted HF energy back from the secondary side to the primary reservoir cap.

> It causes an AC line frequency (plus harmonics) 'leakage current' from the AC mains into
> the secondary circuits.

Well, I've yet to see a digital computer that's hum-sensitive. But an
audio device? Well . . . hmmmmmmm.

[Mike Rivers]

On Apr 9, 1:31 pm, Eeyore >

> The answer here would be to make 'audio grade' laptop power supplies. I'm
> considering it. You can't blame external audio kit for the leakage current from
> the laptop.

Nor can you blame the laptop computer for being a bad player in an
audio system. The people who design laptop computers don't design them
for that purpose. The problem is with the system engineer, who's often
as not first a drummer or guitarist.

[g]

On Apr 9, 1:28 pm, Eeyore >
wrote:
> Mike Rivers wrote:
> > Eeyore wrote:
> > > Mike Rivers wrote:
>
> > > > What capacitor?
>
> > > The 'Y cap' that bumps unwanted HF energy back from the secondary side to the > primary
> > reservoir cap. Most SMPS designs have it (whether 2 or 3 wire).
>
> > > > And if the capacitor is leaking, why not replace it with one that isn't defective?
>
> > > It's not defective. It's doing what it's meant to do (for EMC).
>
> > I'm afraid I've lost the threa here. I had to think hard before I
> > figured out what SMPS meant. I thought we were talking about ahum
> > problem,
>
> We are.
>
> > not an EMI problem, but it's easy to get derailed when you
> > know something.
>
> > I'm not familiar with the design of switching mode power supplies. I
> > just replace 'em when they stop working, so I don't know what the "Y
> > cap" is and why there would be unwanted energy at the secondary
>
> Due to the high frequency switching of the SMPS along with the various consequences of
> practical transformer design.
>
> > and that you'd want to couple back to the primary.
>
> To meet the EMC compliance specs.
>
> > However, if it causes a problem with the audio, it's an inappropriately applied design.
>
> It causes an AC line frequency (plus harmonics) 'leakage current' from the AC mains into
> the secondary circuits. That's where yourhumcomes from when the laptop is connected to
> grounded audio equipment as the leakage current finds a path togroundthrough the audio
> interface.


If, the power supply is isolated, leakage current can exist. If the
power supply output has one side tied to ac comm on the 3 prong plug
input, there is no leakage current, but then you have a ground loop.
The leakage current can cause a high Z ground loop, but that should
not be a problem.

greg

[Eeyore]

Mike Rivers wrote:

> Eeyore >
>
> > The answer here would be to make 'audio grade' laptop power supplies. I'm
> > considering it. You can't blame external audio kit for the leakage current from
> > the laptop.
>
> Nor can you blame the laptop computer for being a bad player in an
> audio system.

No ? The fact is that laptops weren't designed to be used as professional recording
devices of course. Also, their designers are clueless about audio.


> The people who design laptop computers don't design them
> for that purpose. The problem is with the system engineer, who's often
> as not first a drummer or guitarist.

You use a grand title there for someone's friend !

Graham

[Eeyore]

g wrote:

> If the power supply output has one side tied to ac comm on the 3 prong plug
> input, there is no leakage current, but then you have a ground loop.

You can't win can you ? At least not with the manufacturer supplied power supplies.

Graham

[Laurence Payne]

On 9 Apr 2007 11:55:45 -0700, "Mike Rivers" >
wrote:

>> The answer here would be to make 'audio grade' laptop power supplies. I'm
>> considering it. You can't blame external audio kit for the leakage current from
>> the laptop.
>
>Nor can you blame the laptop computer for being a bad player in an
>audio system. The people who design laptop computers don't design them
>for that purpose. The problem is with the system engineer, who's often
>as not first a drummer or guitarist.

Maybe it's surprising how many laptops DO function very well indeed as
a portable recording solution. All of mine have, so far (touch wood
:-) My biggest problem has been that ridiculously fragile and
insecure 4-pin Firewire port.

[Mike Rivers]

On Apr 10, 1:00 pm, Laurence Payne <lpayne1NOSPAM@dslDOTpipexDOTcom>
wrote:

> Maybe it's surprising how many laptops DO function very well indeed as
> a portable recording solution. All of mine have, so far (touch wood

The two of mine do, also. But with all the people who have trouble
with them, either the computer manufacturers or the users must be
doing something wrong.

> :-) My biggest problem has been that ridiculously fragile and
> insecure 4-pin Firewire port.

Since neither of my laptops have a Firewire port built in, that hasn't
been a problem. In fact some laptop Firewire problems have been
resolved by using a PCMCIA Firewire adapter rather than the built-in
port, and most of those have 6-pin connectors, though they don't carry
internal power out through the connector, most likely because it (or
enough of it) doesn't go to the PCMCIA connector. So I've been
tempting fate (so far, successfully) by using the laptop and audio
interface each with their own AC power supply. But since neither power
supply has a safety ground, the only way I'd have a ground loop
through the power system is if I get electrocuted. <g>

By the way, I have a Hum-X on the way for a review. Hopefully I'll be
able to figure out what makes it work without resorting ot a hacksaw.
(I hope Ebtech doesn't read this newsgroup).

[Laurence Payne]

On 10 Apr 2007 12:21:50 -0700, "Mike Rivers" >
wrote:

>> Maybe it's surprising how many laptops DO function very well indeed as
>> a portable recording solution. All of mine have, so far (touch wood
>
>The two of mine do, also. But with all the people who have trouble
>with them, either the computer manufacturers or the users must be
>doing something wrong.

Yeah. Some just have noisy power supplies, which manage to get into
the recording despite electrically isolated external audio interfaces.
More of an issue, I think, is that a large percentage of users are
dabblers. They're the ones who'd have laced the tape wrong, spilled
tape all over the floor the first time they tried a rewind, been
incapable of setting up a gain structure to give a reasonable noise
floor....etc. etc. It's got much easier, but not THAT easy.

[[email protected]]

Let us know if you can figure anything out once you have one of the
mysterious Hum X devices. I was rather disappointed to learn that
even if I got a 6 pin firewire port as a PCMIA card, that it still
wouldn't be able to power my audio interface. I thought it would be
rather nice to be able to power a decent audio interface and my
computer all without using AC power...but I guess I was being overly
optimistic.

-Andrew V. Romero

Mike Rivers wrote:
> On Apr 10, 1:00 pm, Laurence Payne <lpayne1NOSPAM@dslDOTpipexDOTcom>
> wrote:
>
> > Maybe it's surprising how many laptops DO function very well indeed as
> > a portable recording solution. All of mine have, so far (touch wood
>
> The two of mine do, also. But with all the people who have trouble
> with them, either the computer manufacturers or the users must be
> doing something wrong.
>
> > :-) My biggest problem has been that ridiculously fragile and
> > insecure 4-pin Firewire port.
>
> Since neither of my laptops have a Firewire port built in, that hasn't
> been a problem. In fact some laptop Firewire problems have been
> resolved by using a PCMCIA Firewire adapter rather than the built-in
> port, and most of those have 6-pin connectors, though they don't carry
> internal power out through the connector, most likely because it (or
> enough of it) doesn't go to the PCMCIA connector. So I've been
> tempting fate (so far, successfully) by using the laptop and audio
> interface each with their own AC power supply. But since neither power
> supply has a safety ground, the only way I'd have a ground loop
> through the power system is if I get electrocuted. <g>
>
> By the way, I have a Hum-X on the way for a review. Hopefully I'll be
> able to figure out what makes it work without resorting ot a hacksaw.
> (I hope Ebtech doesn't read this newsgroup).

[[email protected]]

On Apr 9, 5:47 pm, Eeyore >
wrote:
> g wrote:
> > If the power supply output has one side tied to ac comm on the 3 prong plug
> > input, there is no leakage current, but then you have a ground loop.
>
> You can't win can you ? At least not with the manufacturer supplied power supplies.
>
> Graham

Graham,

I understand that 2200pF caps compromise the isolation of the power
supply, but at
200 Hz, they have an impedance above 350 kohms. This might harm a
pristine audio
connection, but for most cases it is surely orders of magnitude less
problematic than
a dead short from the safety ground to the computer chassis.

I just found this thread from a problem I was having connecting my
Dell Inspiron 8600
to an external power amp. VERY bad noise. Of course, the PA probably
has a
flawed input connection, but that is not helped at all by the Dell
supply, which has
the ground side of its DC output connected to the safety ground on the
three-wire
plug. Why??? Anyway, one of the replies to this thread stated that
the newer Dells
have two-wire plugs. Sure enough, I swapped over to a supply from my
son's newer
Dell and my problem is gone. Not a subtle difference, either.

Scott

[Chris Hornbeck]

On 14 Apr 2007 18:28:56 -0700, wrote:

>I understand that 2200pF caps compromise the isolation of the power
>supply, but at
>200 Hz, they have an impedance above 350 kohms. This might harm a
>pristine audio
>connection, but for most cases it is surely orders of magnitude less
>problematic than
>a dead short from the safety ground to the computer chassis.

The noise comes in big spikes at much higher frequencies. Many,
if not to say most, of the problems (especially Mystery Problems)
in modern electronics arise from out-of-band stuff. And
they modulate down.

We'd all better just get used to it, or ready for it, as
the Spirit wills. That's the cards as dealt.

Much thanks to all,

Chris Hornbeck

"Beauty will save the world."
- Feodor Dostoevsky

"Information is not knowledge. Knowledge is not wisdom. Truth is not
beauty. Beauty is not love. Love is not music."
- Frank Zappa

[pstar]

On Apr 14, 8:56 pm, Chris Hornbeck >
wrote:
>
> The noise comes in big spikes at much higher frequencies. Many,
> if not to say most, of the problems (especially Mystery Problems)
> in modern electronics arise from out-of-band stuff. And
> they modulate down.

Yes, that's a very valid point for debugging stubborn problems. On
the other hand, the point of my post was that simple ground-loop
problems are not to be discounted because these other potential
problems exist. Power supplies that connect the power-line safety
ground to the low-voltage laptop chassis are, IMO, the first factor to
eliminate in debugging audio hum and buzz problems.

Scott