What exactly does a D.I. do?

[aframe9999]

I know that is changes a high-Z signal into a low-Z signal. But what does THAT do and why do I need a D.I.?

 

I realize that LowZ works much better for long distances (i.e. a snake) but why else?

 

I've got an acoustic with a piezo pickup. no active electronics or anything. plug a cord into the guitar and the other end in to the P.A. (no onboard volume or eq etc. just a straight shot to the board) But I have to have the trim on the board all the way up to get even a moderately decent signal. and I get lots of hum.

 

Is that because of impedence mismatch? would a Direct Box make a difference?

[fet]

Yes, a direct box/preamp will make a big difference. FWIW, I like the L.R. Baggs Para-Coustic DI - works great for guitar to PA applications. Not to plug 'em, but this is a nice unit - provides boost, cannon and 1/4 inch outputs, phase reverse, several bands of boost/cut EQ. I believe Fishman and Tech 21 also make similar products. Hope this helps.

[gtrmac]

It has a transformer or active electronics which boost and balance the signal to match it with a microphone preamp. The balanced line can also reject induced hum by using common mode rejection, whereby one signal is phase reversed producing a cancellation of the hum at the amp, when the signals are combined. I like the passive DI's personally but only if they have high quality transformers like Jensens. You can even use them backwards for re-amping stuff or use two to run a guitar cord between two rooms. You can't do that with the active ones.

 

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Mac Bowne

G-Clef Acoustics Ltd.

Osaka, Japan

[gtrmac]

It's also the guy who yells a lot and insults the recruits in boot camp. makes em do pushups and that sort of thing.