From: heke@stekt.oulu.fi (Heikki Paananen)
Subject: Re: How do DI boxes work?
In-Reply-To: lancer@oconnor.WPI.EDU's message of 15 Apr 93 15:02:28
Lines: 38
Organization: University of Oulu, Dept. of EE, Finland

In article <LANCER.93Apr15150228@oconnor.WPI.EDU> lancer@oconnor.WPI.EDU (Stephe Lewis Foskett) writes:

>   I'm doing sound for a couple of bands around here and we need Direct
>   Input boxes for the keyboards.  These are the little boxes that take a
>   line level out of the keyboard and transform it into low-Z for the run
>   to the mixer.  Sadly they cost like $50 (or more) each and I'm going
>   to need like 5 or 10 of them!  I looked inside one (belonging to
>   another band) and it looks like just a transformer.  Does anyone have
>   any plans for building them?  Perhaps in Anderton's "Electronic
>   Projects for Musicians" book (which I am having a hell of a time
>   tracking down...)?

An Easy way to solve the problem is to use two op-amps to form the
balanced low-Z output, but this solution does not provide any
galvanic isolation between keyboard (or whatever plugged) and
mixer. If no tight requiremets are demanded and some hum, snap,
crackle and pop sounds (formed by ground loops) can be tolerated,
the op-amp solution is just what you are looking for! (It is
cheap...somewhat $10/DI-box).
Not sure, but Craig Anderton did introduce one DI-box project
in Guitar Player mag years ago (transformerless).....

>   Thanks a lot!

Hope this helps. Email, if more details wanted....

>   - lancer@wpi.wpi.edu -                    - 0{{  MoDiMiDoFrSaSo: -
>   -   Mein Kopf ist ein Labyrinth, mein Leben ist ein Minenfeld    -

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Heikki Paananen                           heke@stekt.oulu.fi
The University of Oulu                  
Department of electrical engineering      -Just a student
Finland
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