This is a really good project for anyone wanting a bells and whistles DI that doubles as a door stop on windy nights.... Seriously though, it is very handy device in any pro audio workshop, PA or recording situation.
The project is a combination of the now deleted DI kit from companies such as Altronics Distributors and JAYCAR, part of the old EA DI kit from the '80s, and a bit of myself. If you wish to build this now, you'll have to do it all on vero board. It utilises the power section of the old EA kit to sort phantom power and 9V battery, with it's momentary LED indicators designed to come on for a few seconds and then fade out to save power. I have also added a mains power capability which gives the best fidelity because of the higher operating voltage. All three power sources can be plugged in and the unit just sorts the best one via blocking diodes. The original kit is useless on phantom power because the ICs specified drain too much current. I fixed this by using TL064 8 pin twin op-amps which draw a miniscule 600uA at idling. Also on the original kit PCBs there is a design boo boo with the phase of the output. 'hot' and 'cold' are the wrong way round, and this is easily corrected during wire-up to the O/P sockets.
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