DI Boxes/ Preamps....

Discussion in 'Effects [BG]' started by carlos_07, Nov 30, 2005.

  1. I've been reading threads for about 2 hours now and I'm just a little confused.

    First of all, what does a DI box actually do? That might sound stoopid to people who use them but I really don't get it. (DI= Direct Input right?)

    Also, if I have a bass pod acting as a preamp do I need a DI box when rehersing/ playing live?

    Finally, if I have my boss pod hooked up to an amp and there's no PA involved then should I have a DI box between the pod and the amp? Or is a DI box just for use with a PA?

  2. if you send an xlr line from the pod to the desk, it will be the same as having a DI. A DI basically boosts the signal of your guitar, so that it is louder, and it can run the distance to the desk without getting noise...

    I think it boosts the signal from -10db to +4db?

    what I don't know, is what is the difference between a signal coming from a bass through a DI, and the signal that runs straight from a mic? are they both +4db? does the mic have a different impedance?
  3. SteveC


    Nov 12, 2004
    North Dakota
    I use a Pod as well. I use a DI to split the signal so I can go to the PA and my amp. If you are just using your stage amp, you don't need a DI.
  4. WalterBush


    Feb 27, 2005
    Yuma, Az
    A DI does not boost signal. It changes from high impedance to low impedance. The -10db and +4db are low and line level, and have nothing to do with impedance, except that high impedance outputs are usually line level and low impedance outputs are usually low level.

    The whole purpose of a DI is to turn an unbalanced, high impedance signal coming out of a pickup into a balanced, low impedance signal, such as a mic puts out. This allows longer cable runs (such as from the stage snake to the sound booth) and lower noise due to the balanced signal. It also keeps your bass from losing volume and high-end information due to impedance mismatch. None of this has anything to do with gain, just impedance.

    You might get better information searching, "impedance mismatch" or "impedance matching" rather than DI.

    Also, the bass Pod is a preamp that happens to send out a balanced, low impedance signal through the XLR out, allowing it to both boost signal and match impedance with the mixer's inputs. No DI is necessary between bass, Pod, or amp; only when matching impedances between your bass and PA or recording gear.

    Oh yeah, DI stands for "direct injection" or "direct injector", depending on how it's used in a sentence :)
  5. congrats, that's far better than just coming in totally green and asking stoopid questions! Thanks for properly participating in the forum!

    so, looks like it's covered, but I'll add my 2 cents.

    DI boxes are purely for connecting to PAs or similar equipment. They take high impedance, unbalanced signals and output balanced, low impedance signals. They do this for several reason;
    - all signals appearing at the inputs to a mixing desk are balanced and of a similar amplitude to each other.
    - balanced signals are less suceptible to noise and interference and hence are ideal for long cable runs.
    - mixing desk inputs are not suited to accepting high impedance sources (resulting in high freq. loss and improper gain structure)

    detail for those interested folk - a balanced input feeds what is called a difference amplifier. This amplifier literally amplifies the difference between it's two input terminals. A properly balanced signal actually has two signals 180 deg. out of phase with each other. Hence, when one signal is at maximum amplitude, the other is at minimum.

    So, the difference amp actually outputs the difference of these two signals (duh!), which is in effect twice the amplitude of either signal by itself. Connecting an unbalanced signal to a difference amplifier creates a situation where one of the amplifiers terminals is fixed at ground potential. Thus, the difference between it's two terminals is only equal to the amplitude of the signal - not twice the amplitude as mentioned above.

    Thus you require a fair bit of gain in order to make up for this lack of signal, and this in turn creates noise. Not only that, but impedance mismatches can also adversely affect amplitude and frequency response - but I won't go into that here!
  6. except for the pod *pro*, i don't think any of the other bass pods (xt and orginal) have xlr out. they only have 1/4 unbalanced out. :confused:
  7. SteveC


    Nov 12, 2004
    North Dakota
    That is correct. The Pro has the XLR. I use a PodXT and I run the output to a DI for 2 reasons:

    - so I can split the modeled signal for my stage amp and PA
    - so I can use an XLR cable for the PA connection
  8. 33degrees


    Jun 4, 2005
    Radial bassbone does everything i need it to do and some.