I am running a new Yamaha mixer with preamp capabilities. I just ordered a DI box to connect in our bass guitar into the mixer. I realize I have to balance the signal in order to do that. The DI converts the standard unbalanced bass signal into a low impedance balanced mic signal. Just a question of curiosity- what is the impedance level of a standard bass guitar? I play the mixer, and that is extent of my musical talents.
The only thing you need to worry about - a little - is the input impedance of the DI - IF the instrument is passive. The higher the input impedance, the better the instrument will sound (as the DI will load it less). I like the Radial Pro48 and the Audiopile.net active DIs. If the instrument is active, a passive DI will be just fine. If the instrument has a piezo pickup, you should have an active DI with very hi input impedance - 1M Ohm or better. I believe that the Countryman 85 meets that, as does the Radial PZ-DI.
You need a di box to convert the signal only if you are going longer distances, which is going to be most of the time, unless the mixer is onstage. If the bass (or other instrument) is within 15 or 20 feet of the mixer, it can be plugged directly into 1/4 inch jack on the mixer. I like the Countryman. The impedence becomes an issue in the connection from instrument to mixer because high impedence offers more resistance to the signal and low impedence offers less- hence the low impedence signal will travel long distances. That's how I understand it.
Actually, I'm not sure I got the technical stuff right, but the unbalanced signal from the instrument is good for short distances, and the balanced signal from a mic or di box is good for long distances. Hope that helps.