RF on my bass!

[sardonic_z]

Hey there all. Just had an interesting experience and thought I'd pass it along..

I have one of those Creation Station desks with the rackmounts right above the main desktop. I'm currently running my whole setup (Digi 002 LE system) off of a MacBook (the slightly older one) that has only one FW port, so I have a firewire hub so that I can use my external drives. This hub sits on the left side of my desk, underneath my SCA preamp kit.

So, I've been tracking some demo bass parts lately through a DI and I've noticed that I was getting some really bad high-frequency oscillations on my tracks, right around 8400Hz, especially at high gain on the C84 preamp, which is the IC-based module cloned from the Millenia. I have two other modules, both A12s, which are transformer-balanced and didn't seem to be as susceptible to the hum problem. At this point I am thinking that my single coil bass is just picking up some interference.

So, I started doing some bass tai chi and noticed that there was some hash on the tracks that would get better when I would sit at a right angle to the laptop. The main HF problem was still there, however, and all the usual stuff, lifting grounds, moving cables around, etc. wasn't having any effect at all. I was getting frustrated and thinking that something might be wrong with the preamps, when I realized that my small portable HD was also sitting right below the preamp. I moved it and, sure enough, the buzz got a lot quieter. Then I realized that the FW hub was still there...

Basically just flipped it on its side and the problem went away.

Moral of the story is, apparently firewire devices emit a really audible and annoying radio squeal in very specific directions. So, don't keep them anywhere near anything that amplifies anything if you can help it.

-z

ps.. as I type this with PT still open I am noticing that any time I touch the track pad an audible ground buzz comes through. Kind of makes me want to stop keeping my cell phone in my front pocket..

[cavern]

that seems to be a problem on older mac laptops only. there have been other reports incl. low level hums, R.F. and even feedback. no such problems with new macs apparently or p.c. the connection on my p.c. is dead quiet and it's right beside my outboard rack.

[sardonic_z]

I'm not sure if I buy that.. my Mac isn't exactly right off the line but it's only like a year old Intel MacBook. Maybe the metal cases on the MacBook Pros offer better shielding. Either way, the worst noise was coming from my FW hub, not the computer.

[cavern]

yeah, it could be the hub but if you do a serch here, you'll find all kinds of firewire problems. all with mac only and mostly older power books. your issue may stem from your hub as you say though or cables.