New computer, issues with noise in audio chain.q

[Gizzmo0815]

Ok so I've got an issue with my setup.

I've recently purchased a nice new laptop to replace my aging HP. It's a Lenovo i7 with 4 gigs of ram (I'll be putting in another 4 soon). And it runs Studio One and the Universal Control software just fine. I've got a Firestudio Mobile, which is being run through and expresscard firewire 400 port. I've also got a pair of KRK Rockit 5 monitors.

So now the problem. With my old computer I could plug in all of this equipment into the nearest outlet to my computer and it worked just fine. However with my new one, there seems to be some kind of interference which is causing an audible hum in my monitors (or headphones if I'm using those).

Here's what I've noticed. If I leave the monitor TRS cables unplugged from the Firestudio and listen on the headphones it sounds fine. As soon as I plug the monitors in (even if the monitor's power switches are off), there's a buzz. Now if I unplug my laptop power cord from the strip it's plugged into, the buzz goes away, OR if I unplug the monitor's power cord it also goes away.

Now...the next thing I tried was running an extension from a different outlet and plugging my laptop into that, which at first seems to have removed the buzzing...however! One thing I noticed about this power cord is that it doesn't have a "ground" pin on it...if I use an extension cord that DOES have a ground pin, the buzz comes back.

So essentially, if I plug my monitors, my laptop, and my Firestudio into a power strip, they're all grounded and I have the buzz in my audio chain.

If I take either my laptop OR my monitors and plug them into an ungrounded extension cord...the buzz goes away.

So the way I have it set up right now, I've got my laptop plugged into a three to two prong adapter and into the power strip. Is this 1) ungrounding my laptop and 2) dangerous?

If so, how can I fix this problem?

I've been looking at power conditioners, but I have no idea if this is the right solution for this particular problem.

Thanks for any help I can get.

 

[Washburn100]

That was some good sleuthing there Gizzmo.

Yep, you have the dreaded ground loop problem. Personally, I would do what you did by using the laptop with the 3-2 prong adapter. Laptops seem notorious for causing that problem.

Now, that said, I by no means am an electrical person and I suggest more research into the ground loop problem.

 

[Gizzmo0815]

Yeah...from everything I've read it seems that I've got a ground loop issue. Given that I've just got my laptop plugged into my surge protector with the 3 to 2 prong adapter, it seems to be working fine and I've got no more buzz. I suppose as long as the surge protector is working alright it should be good...the plug is good and secure, so the only odd bit is that the laptop remains ungrounded. Otherwise I'm fine with it.

I think that's one of the most annoying aspects of home recording...not necessarily knowing what the problem is right off the bat (lack of experience)...however, it is extremely rewarding when you solve one of these goofy issues yourself ;-)

 

[dgatwood]

This is a little peculiar. Lifting the ground on either the computer or the speakers fixes the problem? That's a much more subtle problem than most. Usually, you can immediately conclude that one device or another other is producing a lot of noise and adding a ground (a single working ground) causes the hum. In this case, it's only having two grounds that causes it, which likely means that either:

1. The lower resistance to ground and/or extra capacitance somewhere is wrecking some of the power filtering in the laptop. Switched mode power supplies can be cranky, particularly if they are brain damaged....

2. The improved ground means that now there is suddenly a lower resistance path from the Presonus's power supply circuit to ground through the signal ground than through the earth ground in the power supply, and since the signal ground is connected to each input through a resistor (or several), a small portion of the power supply's noise bleeds through those resistors into each input, and probably into some of the little power amplifiers that provide the headphone output and stuff as well.

3. The hum is really there with either one plugged in, but just isn't loud enough to be audible.

4. The improved ground means that now some poorly designed amplifier circuit in the Presonus has started oscillating. (Unlikely, but maybe in theory....)

If you want to get rid of the noise without ground lifts, odds are you can fix it by unfloating... something... probably the Firestudio's signal grounds, but the only way to know for sure is to experiment.

Buy a power plug and a spool of 10-12 gauge stranded copper wire at your nearest hardware/home improvement store, Wal-Mart, wherever. Fasten the wire to the ground pin of the power plug and thoroughly tape over the other contacts with electrical tape so that even if the wire were to work its way loose, there would be no possibility of it coming into contact with either the hot pin or the neutral pin. Now plug in the plug and touch the ground wire to... say the outside of an XLR or 1/4" plug connected into the Firestudio. See if the hum goes away.

If that doesn't help, try touching it to any exposed metal on the speakers, to exposed metal on the laptop (NOT any of the ports, please...), or exposed metal on the Firestudio's case. Then create an appropriate grounding pigtail to ground the crap out of whichever piece of gear made the noise go away. The basic idea is that you make a short extension cable with a plug on one end and a jack on the other (so that you don't give up an input or an output) and on the plug end, you also fasten the shield to that 10 or 12 gauge copper wire.

For example, if grounding the computer's case made a big difference, try using that audio input that everybody has but nobody uses. For that, just take an 1/8" mini cable, cut it, and ground the shield. You're not going to use that jack while recording anyway, so there's no reason to make a proper pigtail (which is hard because 1/8" connectors are a pain in the backside to work with).

If grounding the Firestudio helped, make yourself a foot long XLR cable (or just use an existing cable) and solder the wire on the male end where it plugs into the Firestudio. Solder the wire either to the ground lug (if grounding the case or an XLR connector helped), to the ground pin (if grounding the metal back of a 1/4" cable helped), or to both if you want to be thorough.

If grounding the speakers helped, get or make a 1/4" cable (or whatever kind of cable you use to connect your speakers to the FireStudio) with an end that you can take apart. Solder the ground wire to the shield at the speaker end.

If none of these help, try making a ground bus. Build a pigtail for all three pieces of equipment, connect them all together, and connect them all to the ground on the power plug. That's almost guaranteed to fix any grounding problem you could realistically encounter.

 

[Steenamaroo]

i've read about, and had laptop ground issues.

in my case with dell vostro 1500 and mbox 2, i get mad buzz on mains power, and slight buzz on battery power.

two possible solutions were available that may help you.

one was to remove the ground pin which has been discussed and generally doesn't seem to be recommended.

the other is the solution i use.

turns out, the grround of the laptop is different to mains ground.
i made a cable that plugs into an audio jack WITH ONLY THE SHIELD WIRED.
the other end goes to a mains plug wired to EARTH ONLY.
by using this, i'm directly connecting the laptop chassis to mains earth.

boom...no more more buzz

i don't know if your firestudio uses mains power, but a way to test if this solution will work for you, is to plug in a mains powered device via firewire, for example.

the reason i say this, is if i plug in my 003 over firewire, the buzz disappears. this is because laptop chassis is getting to mains ground through the firewire shield.

**edit. didn't see that this has already been suggested.

The basic idea is that you make a short extension cable with a plug on one end and a jack on the other (so that you don't give up an input or an output) and on the plug end, you also fasten the shield to that 10 or 12 gauge copper wire.


If none of these help, try making a ground bus. Build a pigtail for all three pieces of equipment, connect them all together, and connect them all to the ground on the power plug. That's almost guaranteed to fix any grounding problem you could realistically encounter.