Hi guys,
My first post here. I found this thread while searching the Net for possible solutions to laptop computer
power supply noise problems. I decided to join up, partly because I am a musician and recording/sound tech professionally, and partly so that I could tell you my experiences on this problem (and what I found to be the solution).
I had been going 'round and 'round with this laptop noise problem for a few years- ever since I purchased a Sager (Clevo) M570-TU laptop for audio work in Aug. 2009. I typically use my M-Audio ProFire 2626 audio interface for recording work, along with various other audio gear-
Mackie 1402-VLZ3
mixer, PreSonus HP4 headphone amp,
etc.. When using the
system with my Sager laptop, I kept getting an intermittent noise in my audio, consisting of a low-level, but very annoying, hashy, dirty hum (not primarily 60 Hz, but higher),
mouse zipper noise, and other noises related to computer activity. For example, the frequency of the noise changed when I used a different audio buffer setting on the 2626. I tried a couple Radio Shack "
Ground Loop Isolator" stereo cable assemblies between the ProFire 2626 and my
mixer, which sometimes lessened the noise. But I would still get the noise in other equipment in the room, such as a
bass guitar amp.
I found that if I disconnected the laptop
power supply and ran the computer on its internal battery, the noise went away completely. This pretty much narrowed the problem down to the
power brick, but I was at a loss about how to eliminate this problem, short of getting an expensive linear
power supply for the laptop- I know that 13.8 VDC
power supplies are common, but an 18 VDC supply capable of 6 Amps of
current is probably harder to find, and more expensive. I lived with the problem for way too long. When I heard some of this noise getting onto a vocal
track I was recording for a client, I said, ENOUGH.
At first, I assumed that the
power supply was generating this noise. But it seems more likely to me that the
power supply is acting as a path for noise generated in the laptop to travel back up through the DC cable, the
power brick, and onto the AC
power circuit via the
ground pin. I don't have the test equipment to prove this, but that's my impression. If it was just the
power brick generating the noise, why would this noise be affected by activity on the computer? And, when I
disconnect the DC cable from the laptop, the noise goes away, even though the
power brick is still plugged into the AC
outlet. What's interesting to me also, is that the laptop noise is apparently NOT transmitted through the firewire cable to my audio interface- in that case, I would hear the noise in my audio even when running the laptop on the battery, no?
The solution? Lift the ground pin of the laptop's power supply with a 50-cent 3-wire to 2-wire AC adapter, like the one G15 pointed to above. I have not experienced any of the annoying "
power supply" noise since.
Now, I can understand the
safety concerns about lifting the
ground on an AC
adapter, but practically speaking, we're not talking about a hazard of high-voltage AC on the laptop side here. We're not using a
power tool with a metal casing. Any failure of the
power brick on the AC side would be confined to the
power supply, right? And besides, as some of you have observed above, many laptop
power bricks come with 2-prong AC plugs. What,
safety is a concern for some laptop
power supplies and not others? I think the hazard is minimal at best. And, AT LAST, I have NO noise related to the laptop's
power supply, in my audio
system. I have gone over to the dark side, the ground-lifted side, the QUIET side.