yo!

i had alot of problems with buzz from some of my stuff using laptop-style ac-adaptors. funny thing was that sometimes it wasnt there and i didnt know why. after a few (read: a lot of) hours spent on the internet i got the solution from a guy i spoke to irl. naturally...
dont know if your problem is the same as mine but it could be... so:

when the laptop was plugged in to the same power outlet as the mainmixer and monitors i had the buzz sound.
and when they were plugged in to different outlets the buzz was gone.

i got just one power source in my making-music-closet but fortunately it has two outlets. and theyre not just like a two-outlet power strip fixed to the wall because if they would. i'd have to find another source for my laptop. i've got some stuff that's run with laptop style adaptors and when i checked they made the same buzz. so now i have power strips from the two different outlets. one for my mixer and monitors and all of the other stuff that dont make the buzz. and one that carries all of the buzz making adaptors.

so now life is good.

first forum post yo! i'm getting a 404 tomorrow so i really needed what i've just found: sp-forums.com! whut whuUT!!!

mines buzzing but i think mice are chewing on my rca cables,

last year a mouse would always crawl on me when i was sleeping.

Welcome aboard, yeahkarl! Did you get your 404 today?

Master Lo, you gotta set some traps, homie.

man, you're sure it was that same mouse every time?!

the 404 inherently has a few noises and such.. wouldn't be surprised if the recording part of it also has its nuances and strange quirks!

flashing lights on the 404 can be heard as faint pulses,
turning the volume up beyond about 3/4 also introduces undue noise..

still a loveable box.. so much so that I'm finally getting another one in a week or so.. I feel like im missin out . . almost 50 battles gone by and I've not entered a single one!

It's funny how the sp494 is better on batteries, yet the MPC500 is better on mains power.. guess it goes to show akai have got everything backwards

madmantis: yeah the 404's been on my lap for the last 5 days ... took a little time but now i got most of it.
feels like im baak in school, studying the manual like a... i dunno.
pc

You can minimise the risk of ground hum by making sure all your gear that has a ground is plugged into the same grounded AC outlet. The easy way to do that is with a single AC socket strip with enough outlets for your gear.

Next, whenever possible, everything feeding your mixer that has a volume control have set to as loud as possible. Turn the listening volume down to taste on the mixer. Reason is that a mixer is a bunch of amplifiers and that means any noise picked up on your cables is going to get amplified just as much as the signal in the cable. If the signal is as loud as possible in the first place, then the mixers amplifiers don't need to be boosting and so won't amplify the cable hum/noise by much. If you have a separate power amp or powered speakers, use the mixers main fader close to maximum so the next amplifier down the line isn't boosting so much. See the pattern in level setting? High to Low > High to Low etc and never Low to High if you can help it.

Try not to plug amplified gear (like the 404) into inputs meant for guitars or microphones - they are very sensitive and will pick up more noise.

Try not to use headphone outputs - they are often not as good quality as a proper line output - they aren't meant to feed something that can amplify.

With turntables, somewhere there must be phono preamp, either in the turntable or a separate box or in your mixer. Normally, you'd ground the TT to whatever it's RCA cables are feeding provided that that is grounded. If that isn't grounded then try adding a wire from it's case to something in your rig that is.

You can try adding grounds safely provided you know you have something that actually is grounded. Some mixers might not be grounded if they run off an AC "wallwart" transformer but your power amp should be (and if that's in the mixer, then that ought to grounded already anyway).
Lightweight auto jump-start leads might be handy for trying out extra ground connections since they have handy clamp connectors.

If all that fails, I think you're into "ground-lift" territory and there are some special isolators for that as already mentioned.

Good Hum-huntin'

Jim