Any way to get rid of this hum - laptop output?

Hi everyone,

I was wondering if anyone had suggestions on this apparent grounding problem I am having. Some background:

I have a newish laptop that I've been using with SONAR (an HP DV6125, dual core) with a built in Realtek audio chipset.
For serious use I use my MOTU firewire audio device with this.
However due to the convenience, I often use this laptop for practice away from my studio where I don't have my MOTU.
I've been using the built in Realtek audio and it works great with SONAR and other applications especially with ASIO4ALL.
What I do is hook the line out using a miniplug to dual 1/4" Y-adapter, into the second channel and aux return inputs of my amp (nice fullrange acoustic image lightweight amp), so essentially I have control over each channel sent from the laptop, and can play my instrument hooked into channel 1 along with this.

This has been really handy for practicing away from the studio and the audio output sounds very good. So here's the problem. This setup sounds great as long as the laptop is hooked up this way and running on internal batteries. The moment I plug in the power supply, I get this God awful hum. I have tried everything I know - I plugged both the amp and power supply into the same outlet to eliminate potential ground loops, tried a better quality power strip, tried a different power supply, but nothing helps.
The interesting thing is if I plug in headphones to the laptop, I don't hear this hum audibly - its only when plugged in to the amp that this occurs.

Does anyone have any ideas on how to solve this? I can continue to use battery power but that means I have to shut down and recharge periodically.

Hi Noel

I think a lot of us who use laptops have exactly the same kind of problems, some have tried lifting the ground or using three to two prong adapters. You could have a look at the ground hum eliminator on this page http://www.21best.com/21_best/electronic/security/video/filters/for_sale_.html

I've not tried it myself (it won't fit a UK plug!) but my local music shop has something similar http://www.gear4music.com/Recording_Accessories/Useful_Boxes/ART_Cleanbox_II_ground_loop_eliminator.html which you plug the audio cables into rather than the power supply, but I haven't researched it further as yet.

Suprised to see the CTO has this kind of problem!!!

Andy

PS and as a SP6 user, thanks for a fantastic program

No the amp cord is pretty good - in fact it has one of those RF filter type things built into the end of the cord. AI makes pretty high end components so I'd be surprised if they were the weak link here. The more likely culprit is the poor quality electronics in the laptop itself. And if you were referring to the jack from the comp to the amp itself, its not very high end but its a standard HOSA Y cable.

"HOSA"

You may have just said the magic word. Really, they make the worst shielding out there. I bought two different HOSA Y-cords for using my DBX compressor with the effects loop on my Boss AD-5 acoustic preamp and I was picking up trucker's CB radio signals left and right with both of those cords. I know Frank and a few others here have talked about how bad their shielding is too.

Pmac, if it was a ground loop shouldn't plugging into a single power strip have eliminated the hum?

Yeah, you would think so, and according to the theory, you are in effect creating a 'star ground' system, but sometimes the only thing that works is breaking the ground. My laptop had more of a 'sizzle' than a hum, so it may have been some other grounding issue, but 3 to 2 fixed it.

I don't know if this would have anything to do with yours or not, but the only laptop I ever had was an old one with a 286 processor. I opened it up once to try to change the BIOS chip and noticed that there was a ground wire attached to the keypad (it had a metal base). So maybe you're right about your occassional keypad problem and the ground having something in common.

noel, i'm almost certain the laptop is the problem. i've owned a couple dells and both had the humming issue. on battery they were fine. rather than spending money on an electrician spend it on a decent internal laptop card (like an indigo or whatever) and use that instead of the realtek. believe me, i've tried all sorts of things and i've had my laptop plugged into all manner of different outlets including battery backups and the only thing that fixes the hum is to unground the power cord.

Jack, yeah I wont be using the onboard sound for anything serious - definitely not for recording. I have my MOTU for that.
Its surprising that electrical specs in laptops are still so dismal these days. This is supposedly a HD audio device too and in theory by the HD audio spec, manufactures are supposed to conform to more stringent specifications. I suppose nobody enforces these.

By the way, any of you guys ever try to take a laptop apart? Man, I will never go through that again! Uh uhhh....

ORIGINAL: Joe Bravo
By the way, any of you guys ever try to take a laptop apart? Man, I will never go through that again! Uh uhhh....

yes. it was the most pointless 2 hours i've spent in my life...

ORIGINAL: Joe Bravo

By the way, any of you guys ever try to take a laptop apart? Man, I will never go through that again! Uh uhhh....

Ever have a mechanic hand you a box of extra parts when he's done fixing your car? That's the way my last experience taking a laptop went... NOT fun! lol

Noel: While you're probably ok, I'd be a bit concerned about using a power ground lift. It can be dangerous... there's a reason they have a ground on amps and laptops these days. Just something to think about.

Corey

What, you8 don't think that's me?

I've put up several videos of him at YouTube in recent months. Did you hear he's gonna do a couple of concerts near his home in Oregon where he's going to play every song from the trilogy? I'd love to go but it's just too far for me to travel and justify the expense. I would sure love to videotape it though. I hope somebody else does.

Well he just had the first of two eye surgeries and this concert is suppose to pay for the second one. They posted it on his website a few days ago. I just found out about it too. I drove out to Louisville with a friend to see him solo around ten years ago. He played for four hours! I left wondering how any human being could possibly remember the words to so many songs without the use of music sheets, and he seldom missed a word. Johnny Cash is the only other person I've ever known who could do that, but Johnny's memory is legendary. I once saw him on some country cable show where the host asked him about some old poem he used to quote from back in the 60's. Cash said he had nearly forgotten the poem after all these years and then proceeded to recite the whole thing. And it was a very long poem; I think it took him a good five minutes to recite it, and he didn't skip a beat.

ORIGINAL: Noel Borthwick [Cakewalk]

So whats the theory - although I plugged the amp and adapter into the same power strip, why was I still getting hum? Also should I bother getting a hum filter for this, now that the problem was solved with this simple solution?

Do you guys think I should get an electrician to look into my house wiring?

Late to the game here, but I'll fire with a theory: It's noise from the switching power supply traveling up the ground AC pin and into your audio lines. This is why it's much nastier than the classic 60Hz + overtones sound of a ground loop.

I get the same issue on both my laptops, regardless of the audio interface used (either on-board, or fireface), and it happens everywhere I've tried it, even on old houses with no ground at the AC recepticle.

I wouldn't bother with the electrician, nor the hum filter, especially if your adapter is all plastic (I'm sure it is). After all, AC ground doesn't go to the laptop (check it with a continuity meter) so it's not adding safety to the computer, just to the power brick which, being all plastic, presents little shock hazard.

I suspect this is one reason apple uses ungrounded power supplies for their laptops.