DC Offset with MBox2 -- any solutions, please?

[JRob]

Okay, I've heard about it, I've experienced it. At first, it only happened with a pair of cheap condensor mics that I used in live applications. However, now it's happening with EVERY analog input -- no matter whether it's condensor, dynamic, or a line input from another piece of gear in the basement.

(For those who don't know, that's the phenomenon when the waveform in your recorded channel "sits" or "hangs" on one side or the other of the center line, instead of being symmetrically distributed. Usually, when nothing's happening, you'll see your meters sitting at about 1/2 way up -- and it's easy to overload the channels.)

I'm running an MBox2 with a 12" G4 Powerbook, ProTools LE 6.8.1

Is there any fix for this? I know about the tool for removing DC offset, and that's all well and good -- but if there were some way to prevent it from happening in the first place, that would be much, much better. I don't even know for sure whether this might be a software-related problem (and as such, might it be fixed by upgrading to 7.x?)

I've googled quite a bit (and searched here quite a bit) for a definitive solution, but I have yet to find anything. Help me -- I used to love my MBox, but now I'm becoming reluctant to even deal with it.

[Craig F]

is it the mics or the M-Box2?

if you have a dummy load (a 50 ohm resistor between pins 2 & 3) w/ the gain cranked up do you sill see the offset?

[tele_player]

I bet the answer is yes to that.

[JRob]

I can try the resistor trick, but since it happens with line inputs and mic inputs, and happens with a variety of mics -- I'm going to guess in advance that the answer will be "yes, it's the box and not the mics". If that turns out to be the case, does anyone have a recommendation? Would it mean that I should return my MBox, or is there something that can be done in cases like this? I guess I'm wondering whether it's something that others have experienced, or whether I've just "got a problem."

[JFreak]

Insert a hardware hi-pass filter to your recording system.

[tele_player]

An A/D converter should introduce minimal DC offset. If the Mbox does it, with various source signals, something is wrong with the Mbox.

JFreak - why do you suggest a hardware hi-pass filter?

[JFreak]

JFreak - why do you suggest a hardware hi-pass filter?

Just a gut feeling. Many times I've noticed that if you just help the converter a little, the problem goes away even if the reason were not completely eliminated.

[tele_player]

Interesting concept, but I don't think it will help. Since he's tried several mics, including condensers and dynamics, and line inputs - the DC offset isn't being caused by a defective external device, and a filter between the external device and the Mbox input won't change that.

If he gets a DC offset when the mic inputs are connected through a resistor, there's something wrong inside the Mbox.

[JRob]

If he gets a DC offset when the mic inputs are connected through a resistor, there's something wrong inside the Mbox.

I'll confess to not knowing what to do with this information. How do I connect the mics through a resistor?

Edit: sorry, I see it mentioned in a previous post. I'll contact my EE dad, and give it a shot.

[JRob]

...so am I the only one with this problem? Is there any hardware thing I can do to "reset" the inputs? It was all beautiful when I first bought the box; now I kinda don't want to use it, and I'm outside of my one-year warranty. :-(