Transformer balanced, phantom powered active DI

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Transformer balanced, phantom powered active DI

Postby chris p » Fri Oct 27, 2006 7:11 pm

Hi y'all

This must be the easiest DIY project in the world that produces a functional result. Its a guitar DI box based around a Burr Brown OPA2604 dual opamp.

You start off with a $38.50 DI kit from JLM Audio, and get a JLM 1:4 tranny ($44) while you're at it - http://www.jlmaudio.com/JLMDI.htm. The only extras are an XLR(M) socket, an LED and a box.

Here's the hookup, based on Joe's webpage schematic -
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The genius is in wiring the tranny backwards, so you get a 12db drop rather than a 12db boost. This returns the opamp output to a level that is just right for plugging in to a preamp, while balancing the output so you can use the OPA2604 opamp on phantom power (without the tranny, Joe recommends swapping to a TL072 FET opamp.

So simple, yes? Here's my build ...
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You can add in 9V battery power if you want, which also allows you to put in a ground lift. You might want to do this is you are DI'ing something with a power source, but I wanted this just for guitars, so I kept it as simple as possible.

And what would you call such a military grade DI from Mr Malone?
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chris p
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