5 Replies Latest reply: Dec 4, 2010 12:42 AM by IlMolto
IlMolto Level 1 Level 1 (5 points)
Hi guys,

Anyone experiencing this? I have an Astro Gaming MixAmp that is connected to the line out of my Mac Pro. I have this setup so I can listen to music through iTunes while playing my PS3. Anyway, I get a weird buzzing sound coming into my headphones (connected to the MixAmp). When I disconnect the cable that's connected to the line out on the Mac, the buzzing stops.

I also posted another thread about a buzzing sound coming from the power supply of my Mac. The buzzing coming out of the line out sounds very similar to the buzzing coming from the power supply. Do you think they could be related?

Anyway, I thought I'd post my experiences here just to see if anyone else has noticed a buzzing sound coming from the line output. Please post your experiences if you have.

Thanks for reading and I hope to hear from someone soon.



Mac Pro 3.2GHz Quad-Core Intel Xeon "Nehalem" (Mid 2010), Mac OS X (10.6.4), 12GB 1066MHz DDR3 SDRAM
  • Deborah Terreson Level 4 Level 4 (1,000 points)
    Could be that the line-out cable has a pinched section somewhere and the shielding is compromised - I had a line-out extension cord that produced a wicked buzz which drove me nuts until I sussed it out. Guh! Cheap patch cords are the bane of clean sound, for sure.. ALSO! that pre-amp may not be on a circuit that's properly grounded. MacPros are basically ALL ground, but even so, if the house you're in isn't.. and especially that you've an amp.. noise galore!
  • IlMolto Level 1 Level 1 (5 points)
    Hi Deborah,

    Thanks for your reply. It's definitely not the cable because I tested the same cable with my iPod classic. I don't get any buzzing at all when the iPod is connected to the MixAmp. I also connected that same cable from the line out of the Mac Pro to the line in and recorded to see if the buzzing still occurs. Nothing. Just noise. I'm so confused. What could be causing this annoying buzzing noise! I wish I could record a sample and post it on here of what it sounds like. But as I said, when I recorded it the buzzing wasn't there. The only time the buzzing occurs is when I have the line out of the Mac Pro connected to the MP3 input of the MixAmp. And there's no way to route the MP3 input back into the Mac for recording...
  • IlMolto Level 1 Level 1 (5 points)
    I just realised. Of course I can get the input back into the Mac! I'm such an idiot. All I had to do was connect a cable from the headphone out of the MixAmp to the line in on the Mac. Anyway, here's a sample of the buzzing:

  • William Kucharski Level 6 Level 6 (14,890 points)
    I suspect a ground loop; is the mixer grounded? Is it on the same electircal circuit as the Mac Pro?
  • IlMolto Level 1 Level 1 (5 points)
    Hi William,

    Thanks for your reply. I'm not sure if you have ever used an Astro Gaming MixAmp before, but its main use is for PS3 or Xbox connected via USB for voice chat. It's a professional gaming mixer that amplifies the signal and allows you to balance between game audio and voice chat volume. It also has a line in port that is used for injecting your own music while playing. This is what I connect the Mac to.

    From what I've discovered so far, the buzzing is being caused by the USB cable picking up radio interference. However, the buzzing is only audible when I have the line out of the Mac Pro connected to the line in of the MixAmp. It seems the 3.5 mm cable is picking up this interference and sending it to the MixAmp. So the Mac Pro is definitely not the main cause as the buzzing goes away if I disconnect the USB cable. But the weird thing is, if take the cable out of the Mac Pro's line out and put it in my iPod classic, there is no buzzing at all, even with the USB cable connected.

    I'm fairly sure that the USB cable is the main problem because if I bend, straighten or move the cable around while it's connected, the buzzing changes. Sometimes for the better and sometimes for the worse. I've actually been able to completely remove the buzzing for a short period of time by positioning the cable in a certain way. But it's pretty much impossible to keep it in that same position forever.

    Anyway, if you have any other suggestions I'd love to hear them. Nothing will please me more than to get rid of the buzzing. Thanks again for your time.