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Audiophiles HELP!! Rec from 16ch 'board -> laptop = noise... but only when laptop on AC?

Submitted by Macinjosh on January 23, 2007 - 7:35pm. Other Technology

Ground noise?

I tried recording one of my band's practices using my new(er) Latitude C600 laptop, and a few different softwares. Audacity ROCKS! But, the recording sure didn't.

I'm sitting there going nuts, plugging stuff in and unplugging it, between our 16 channel Yorkville sound board and my laptop. No matter what I do, I've got this overpowering noise coming through, unless I unplug the audio connection. Tried the RCA recording outs, line level left and right outs, the headphone jack on the board, everything. Also tried every possible combination in the recording settings of Windows, the mixer, Audacity.

Finally, I'm thinking "well, it's a laptop. maybe it's not going to work" because I pulled this same stunt with my Blue and White, and got perfect results. Being the troubleshooter that I am though, I just happen to try pulling the AC connection on my laptop... BAM! Noise gone. Crystal clear.

Too bad I only get very close to an hour on battery!

So, I'm thinking I am getting some noise from, the board and the laptop being on the same circuit? Tried plugging in as far away as I could get from the board, on a different room's AC... no dice.

Plugging an MP3/DVD player the same way, no trouble and perfect results.

What can I get to throw a) on the AC power of my laptop b) between the board and my laptop ... that will filter out this noise? WTF is it, anyway?

Laptop and board are both grounded three-prong style as far as the wall jack; don't know after that. But I did try this at a gig with the same overpowering noise, so I don't think it's specific to the house's wiring either.

-- Macinjosh

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Dr. Webster's picture

It's fairly obvious that you

Submitted by Dr. Webster on January 23, 2007 - 8:36pm.

It's fairly obvious that you have a ground loop between the mixer and laptop. The loop breaks when you pull the laptop's AC plug because then the laptop is electrically isolated.

First thing I would try is, assuming you don't use it, turning off the phantom power on the mixer. Other things you could try would be to use one of those grounding plug adapters on the laptop's AC adapter, to remove that ground pin from the picture. It could also be that the mixer is an old piece of crap (Yorkville isn't known to make the best-quality stuff) and the internal power supply is leaking current.

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Macinjosh's picture

Cool, I'll try the adapter route.

Submitted by Macinjosh on January 23, 2007 - 8:44pm.

Cool, I'll try the adapter route, and check the phantom power. Jives with the MP3 player having no problem; it's not grounded.

The mixer board definitely isn't a POS though; it's this:

PowerMAX

Though I'll concede that Yorkville's not-new stuff can be rather crappish.

I know it might have seemed a simple enough question; but hey, that board cost ten times what this laptop did, so needless to say I consult before I try.

-- Macinjosh

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Dr. Webster's picture

Re: Cool, I'll try the adapter route.

Submitted by Dr. Webster on January 23, 2007 - 8:53pm.
Macinjosh wrote:
The mixer board definitely isn't a POS though; it's this:

PowerMAX

Ugh, a powered mixer. The possible sources of ground loops just went up exponentially. Sorry, but powered mixers are total pieces of crap.

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Macinjosh's picture

Re: Cool, I'll try the adapter route.

Submitted by Macinjosh on January 23, 2007 - 9:17pm.
Dr. Webster wrote:
Macinjosh wrote:
The mixer board definitely isn't a POS though; it's this:

PowerMAX

Ugh, a powered mixer. The possible sources of ground loops just went up exponentially. Sorry, but powered mixers are total pieces of crap.

All righty then. For what we do though, which is live performance, and which I have done for like 15 years, it's been an outstanding performer and one of the quietest setups I have been around.

-- Macinjosh

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Switching phantom power shoul

Submitted by sfinro on January 23, 2007 - 10:46pm.

Switching phantom power shouldn't matter should it? After all, it is only present on balanced inputs.

I've had a similar problem with my Compaq Evo laptop connected to a Yamaha non-powered mixer. I tried everything - ground cheaters, different inputs and outputs, turning the display off, different cables. The only way to make it quiet was to run it off battery. I eventually put it down to noise coming through from the power supply - switch-mode power supplies can introduce high-frequency noise - and ran the sound from my venerable 9600 with perfect results.

» Romana: 9600 with Sonnet G3/400. 384mb RAM, 8gb + 4.5gb HDD, OS 10.3.9
Davros: Beige G3/266. 384mb RAM, 10gb HDD, OS 10.3.9
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Dr. Webster's picture

A noisy phantom power transfo

Submitted by Dr. Webster on January 23, 2007 - 11:31pm.

A noisy phantom power transformer can cause noise. It's actually pretty amazing the places where noise/signal problems can come from, that you wouldn't think of. For example, have you ever stepped up to a mic, electric guitar in hand, and gotten a static shock from the mic grille? That's not static electricity -- believe it or not, that's AC current leaking out of your guitar amp. The moral of the story is, when diagnosing audio problems, parse the entire chain, not just the component(s) you think are at fault.

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