<br><div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><br>This is frustrating. The buzz is still present even if all the devices are connected to the same AC ground,
i.e. the laptop and the amp both plugged into the same outlet or power strip. It does not make the buzz any softer.</blockquote><div><br>Try a different power strip? Shouldn't be the case, but just in case. Also make sure your outlet is running off the same circuit on the top and bottom, I have been some places where it hasn't always been the case.
<br><br>Couple quick questions, does varying any of the level controls on your interface make a difference in the volume of the buzz? Does it change at all when moving the mouse, or when your HD spins up, or you make your video card do work(Change desktops etc)? Does it exist when nothing is plugged into your interface, or when only certain things are plugged in to it, but not others?
<br> </div><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">I have captured a sample of the buzz (normalized; it's nowhere near this loud) if that helps:
<br><a href="http://www.restivo.org/misc/buzz.ogg">http://www.restivo.org/misc/buzz.ogg</a></blockquote><div><br>To be honest, I am wondering if there aren't a couple of different things adding up in your case, most of the time a ground loop on a laptop, unlike in straight audio, will show up as digital noise that fluctuates as you move the mouse, or videoc ard starts going a bit harder, or your HD spins up. This sounds a bit more like standard interference, of the sort I would expect to find from a poorly shielded or isolated internal audio on the laptop. As such running through an external interface means that you should not have that problem.
<br><br>The audio wiring you were told is an internal problem on laptops, only applies to internal audio, it does not apply to external audio. Internal audio cards are prone for problems because they are poorly, if at all, shielded and pick up lots of interference from other devices, and the general signal flow on a laptop, both power and data, is generally not done for audio quality.
<br> </div><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">I have been told that this is probably caused by the power distribution circuitry within the laptop: it does not separate earth ground from "signal" (I'm assuming USB signal since my audio interface is USB) ground. The buzz certainly sounds more like "computer" noise than 60 cycle hum.
</blockquote><div><br>Again though see above, the problem you are referring to should only affect internal audio, not from an external interface.<br>
<br>And to confirm, your USB interface is bus powered? I assume then you are running it without the power cable for it? Does this problem exist if you unplug your amp, but leave the settings(Gain etc) like you still have it plugged in to your interface(Meaning nothing is plugged in at all)?
<br></div><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">So far the only thing that works is to lift the ground on the power supply. Luckily my audio interface has balanced outs, so I'll try lifting the ground on the balanced output instead, as soon as I can build or locate an adatper which does that.
</blockquote><div><br>A simple cheap DI box will do it fairly well in most cases. They usually have a ground lift switch on them for just such a purpose.<br> <br>If you make your own, a 1:1 transformer will do the trick.
<br></div></div><br><br> Seablade<br>