When you say "terrible low noise", what do you mean? Are you referring to a "60-Hz. hum"?
If so, this can be caused by using the wrong cable to connect your gear together, it can be a "ground loop" where different pieces of gear are plugged into differently-grounded outlets.
Are you using the PreSonus TubePre? I suppose that you are attempting to add "tube coloration" to the mic with this little box?
Why would you place it in the Insert Loop of the Onyx? The Onyx should have a much better mic pre than the one afforded by the TubePre. Sorry, I was editorializing there....
I would think that to get the cleanest, least-noisey signal, you should run the mic directly into the Onyx channel and take the line out from that channel into your Firewire box. I understand that the channel EQ won't affect the signal, but still....
Or you could run the mic into the TubePre and connect that to the Firewire box.
Do you still get the noise when you DON'T plug the TubePre into the system? Please fill us in a bit....

yes its definitly a 60 hz hum...and it gets louder when i turn the gain up ( weel this is obvious). i tried running the mic into the pre and then to the firebox and the noise is still there..yes i am trying to get tube coloration...the noise is with no doubts coming out of the tubepre box. even when i only connect the output to the mixer and no input..
...i didnt get the "ground loop" explanation.well as i write from italy and the voltage here is 220 i had to buy another power supply...oh god...i just realized what the prblem was....i didnt change the voltage...it was on 9v.....ok thank you so much for the answer....i am happy now...and well it might help another ignorant....jeje
bye
LULO

NOW SMOKE IS COMING OUT OF THE TUBEPRE BOX....I WILL LAUGH JUST NOT TO CRY!! WHAT S THE PROBLEM NOW?I THINK I LL THROW AWAY THIS SHIT!!ANYWAY THE DIFFERENCE WAS NOT GREAT FOR THE 2 MINUTES THAT IT WORKED..HARDLY HEARD ANY DIFFERENCE!

Yeah I own that pre mine isn't that noisy but it sure isn't that great, I mainly use it as an extra xlr input.

Too bad, Lulo. I guess that there is something to be said for gear with an internal power supply with automatic voltage switching. By the way, your English is pretty good, even under less-than-ideal situations. Keep the TubePre and put it where you can see it all the time...as a reminder, capiche? I have a Beyer M500 RIBBON mic
sitting on the top of my console.It is dead.That's what happens to a ribbon mic when you TURN ON the PHANTOM POWER!!! It is a reminder to think before I connect. We all learn from our mistakes,no? I am glad that you were not hurt or burned up.CIAO!

i couldnt be more stupid, could i?? i agree...now everything is working fine...the voltage was not 24 but 16!! and i m glad i am answering my own questions but here is another one:

my connection is mic to tubepre and then to the firebox...now...even the tubepre and the firebox have a PAD button...i read on the manual of the tubepre that when using a 48v mic this button should be on...but the sound changes so much...so....any suggestion?

then there is another question.....i just bought the bosendorfer 290 imperial samples and i love it.....but the mac is not very happy...clicks and clicks......i tried changing the buffer size and it works but latency is killing my hands as i play! so whats the best configuration?? stand alone program or au plugin ( use digital performer) where should i put the sample folder? system hd or firewire 800?? any tip is welcome!
thanx again
LULO

The "pad" is simply a circuit that "attenuates" the signal coming into the pre. That means it drops down in level whatever amount is indicated (typically 10-20 dB). This is in case the output from the mic is too "hot" in strength. Sometimes even non-condenser mics need to be "padded"( like when they're stuck in front of a Marshall amp or inside a kick drum). Maybe the TubePre needs to have the Pad "in" whenever a condenser mic is used because the input is very sensitive. But a decent pre shouldn't require that in ALL cases. What are you trying to mic? You are right about changing the sound. Some mics do not "like" to see a pad switched into the circuit. It will affect not only the volume (duuuh!) but also the "tone" (dull or thin). Try setting the input gain down all the way, switch the pad OUT, and then slowly bring up the gain. See how that works with your mic and the source...
As far as the Mac problem is concerned...try David French in the "Digital Audio Recording" section...he's the man for that!

thank u so much guys...you sure answer very quick! yeah i think pad button sucks! the tone gets thin!! very thin...i am trying to record piano and voices....this means i play, sing and record at the same time.....i wouldnt like to have different takes for the piano and the voice mainly because, well you know, it wouldn be right! the essence is there...no metronome and that extra millisecond counts a lot..... so no way jose! i wouldnt blame apple...so i am begining to think of m-audio firewire..do u know about firewire option for onyx mixer?? this is out of topic here....i ll go to the right place and write sth! lets contact david french!
thanx again
LULO