Dell Insprion 1520 very bad recording hum

B

BrettOnTheNet

New member
Hi there

I suspect I should be posting in the Newbie section because I most certainly am a newbie when it comes to audio.

I am trying to do some simple screencast recording on my Dell 1520 Laptop, or for that matter, use Skype, but there is a really bad hum whenever I record.

I have a USB headset/microphone that seems to be OK when I use it on other computers, but on this one (my main one) it's nothing short of terrible (and getting worse).

I am wondering whether there are any simple solutions for me, such as having an external device that does the conversion to digital and just passes the digital signal directly to the computer, bypassing the internal sound card.

I've done a bit of a search for sound cards, but they all seem to have a line-in type input rather than USB input. And because I don't really know what I am looking for I thought I would ask the experts.

Is anybody able to recommend a cheapish external device that will allow me to record sound without using my internal soundcard? Is this even feasible?

Thanks a lot for your help.

Brett
 
Oh, hang on a minute. I was just reading up more on this and I found some pages that said a USB headset won't be using the soundcard anyway because the signal is already digital when it hits the computer. So the analog to digital conversion has already taken place.

Is that right? Is the problem going to be with my headset, rather than with the onboard sound?

Maybe it just doesn't show up as bad on my other computer?
 
Ok. Back again. I've tried a few things - isolating various external components. I seem to get the cleanest (and a tolerable) recording when I unplug my power supply and run off battery.

The only problem is that my battery is basically screwed and I don't get more than a few minutes out of it. So do you know if there is a way of removing this power supply hum but still have the power plugged in? All my USB ports are right next to the power supply so I wonder if that has something to do with it?
 
Try borrowing a compatible power supply from someone who has a Dell and see if the problem is in your particular one, or the notebook design. (If the AC adapter is bad, that could also be why your battery is not charging.)

If a different adapter fixes the problem, replace yours.

If it's *not* the adapter, you'll probably need to consider buying a battery that will hold a charge, or a new computer for what you want to do. You could try to borrow a different USB mic/headset/interface and see if it's less susceptible to noise, first, though.

Good luck.
 
Hi there,
I used to have a dell vostro 1500, which is the same as the inspiron 1520 in many ways.
In fact, I think it might be identical apart from the plastics etc.

Anyway, I had serious trouble with recording hum and buzz when using any usb or firewire audio interfaces.

I don't exactly understand it, but the bottom line was that the chassis of the laptop (and any connected usb or firewire device) is ground.
However, it is isolated from mains ground which stops at your power transformer, if it even goes that far.

The laptop ground was floating a few volts above my household mains ground. This difference in potential allowed me to hear mains hum when recording.

Like I say, I don't completely understand it but as I hear it's a common enough phenomenon in laptops.


My 'solution' was to connect a mains powered usb or firewire device to the laptop.
By that I mean something like a digi 003 which has mains live, neutral and EARTH right to the unit.

Because the chassis of the 003 was continuous with household earth, the body of the laptop was too (usb or firewire shield connects the two device chassis).

I also found that making up a cable to manually mains ground my laptop chassis worked, but I don't recommend anyone should try that.
I'm in the UK where we have three pin mains, one of which is ground.
*This may not be applicable elsewhere*
 
if it's humming because of the ground you need to get it fixed ASAP. Called a ground loop. If that is what it is then basically what is happening is the electricity that was supposed to tapper off through the ground is recirculating through your computer. This can be very bad, and destroy everything.

It has to be properly grounded. Often times a ground loop will generate a buzzing sound. That is the sound of the excess electrical current going through parts of the system that it shouldn't be going through.

It can be quite serious, and you need to make sure first and foremost that your ground is proper.
 
A ground loop is caused by having more than one path to ground; Often two grounds at different potentials.

Anyway, this guy has no path to mains ground which I suspect is the problem.
I may be wrong about that, but it's definitely not a ground loop unless there are racks of gear he's not telling us about.

Brett, does the problem go away or decrease if you switch off the laptop power supply?
In my case the laptop was susceptible to noise from nearby transformers etc, and the laptop PSU was the main offender by proximity.

When switched off at the mains there was much less audible hum.
 
Steenamaroo said:
A ground loop is caused by having more than one path to ground; Often two grounds at different potentials.

Anyway, this guy has no path to mains ground which I suspect is the problem.
I may be wrong about that, but it's definitely not a ground loop unless there are racks of gear he's not telling us about.

Brett, does the problem go away or decrease if you switch off the laptop power supply?
In my case the laptop was susceptible to noise from nearby transformers etc, and the laptop PSU was the main offender by proximity.

When switched off at the mains there was much less audible hum.
Click to expand...

you get ground loops from not having a ground as well. i think I should know. I have had one before. Caused by ungrounded gear.

The current that was supposed to go out the ground circulated in the gear, and caused a hum.

It's better to assume that it is a ground loop, and trouble shoot for that first.

Or let's pretend it isn't a ground loop like you are advising, and then it actually turns out to be one, and fries his gear.............
 
Hi all. Sorry for the delay in responding. Notifications from here were going into my Spam folder so I didn't realise that a lot of people have replied.

I have a short term fix.. I stole my wife's battery :) So I can do some recording now and it's sounding really good.

Power supply off + no external monitor = excellent recording. On this machine there are 4 USB ports, all right next to the power socket.

Regarding the grounding. Steenamaroo is correct ... I seemingly have no path to ground at all. My wall plug for the power supply has only two prongs. And the plug in the adapter (which connects to the lead for the laptop) also only has two prongs. I have a vague feeling that the one I had before this one had three. (But still only two into the wall). In New Zealand we have the third prong for ground.

So it seems there is no grounding.

I have lost a couple of batteries and a couple of adapters so far in 5 years of owning this thing, but never considered that grounding might be an issue causing that. Could it be? It's how it is supplied so that seems odd.

I will try my wife's adapter in it to see if that changes things. Hers still only has the two prongs into the wall though. Why don't Dell make these things with a path to ground? How else is it supposed to be grounded? It seems pretty common with laptops though.

I had wondered about trying a powered USB hub, and might look into that too. I had seen elsewhere that this might fix things, but I never considered that it could be to do with the grounding.

And regarding the potential frying of my laptop... That would be great :) It would finally mean I can get a new machine!

I think I've covered most of the points you guys have made in this thread.

I sincerely appreciate all your help.

Brett
 
Super Producer said:
you get ground loops from not having a ground as well. i think I should know. I have had one before. Caused by ungrounded gear.
Click to expand...

I'm pretty sure a ground loop is usually a loop to ground; Ie more than one path to grounds, both of which should be at the same potential.
The symptoms here are the same as a ground loop, but there's a different reason for it.

I'm not qualified to argue over it, but I suppose it doesn't really matter at this stage anyway.


BrettOnTheNet said:
I will try my wife's adapter in it to see if that changes things. Hers still only has the two prongs into the wall though. Why don't Dell make these things with a path to ground? How else is it supposed to be grounded? It seems pretty common with laptops though.
Click to expand...

It does seem to be the done thing.
The adapter converts to AC voltage ( live, neutral and earth here ) to DC voltage ( + and - ).
The DC ground is at a different potential to mains earth, which I believe causes the problem.

By connecting to a mains interface (or whatever), you create continuity between the DC ground and the mains earth.
This creates one path to mains earth.

BrettOnTheNet said:
I have lost a couple of batteries and a couple of adapters so far in 5 years of owning this thing, but never considered that grounding might be an issue causing that. Could it be? It's how it is supplied so that seems odd.
Click to expand...

I don't think this would be causing your problems.
It's not so much a fault as the way these things are designed.

I guess most consumers aren't going to be worried about moderate susceptibility to interference, so it's probably not a consideration for the manufacturer.

As I say, when I used a mains powered interface (motu 828, digi 003 etc) there was no problem.
It's really use of usb/firewire powered interfaces, or interfaces that use a wall wart that shows up the problem.

I bet if you plugged some kind of audio cable between your laptop and a VCR/DVD player/Hifi, it'd earth the whole setup!
 
Last edited:
mjbphotos said:
I doubt ANY laptop manufacturers have a grounded power cable to the laptop, the standard is the 2-conductor plugs.
Click to expand...
The 3 HPs in our house all have 3 prong connectors, as does the Dell in this topic: 331-0536r1.jpg.

Lenovo looks like they use 2 prong adapters.

Now, maybe you mean grounded from the notebook chassis all the way back to the AC plug. No, not very likely.
 
still_fiddlin said:
Now, maybe you mean grounded from the notebook chassis all the way back to the AC plug. No, not very likely.
Click to expand...

This is the key point.
Whether there's ground to the transformer housing or not, there's never mains earth up to the laptop.
The transformer isolates one from the other.
 
Update, and "I stand corrected," as they say. The real answer probably is, "It depends."

At least for one manufacturer, here's the direct quote from the person that designed these things:
"... there is a resistive connection to ground; there is not a direct coupling of the notebook chassis to the ground on the socket, but it does go through a resistor and capacitor .... changed from a direct connection a few years ago exactly for ground loop issues ..."
 
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