The project is a combination of the currently available 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. 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 orginal 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 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.

At right is the Vero board for regulating whichever power source is used. On this board a larger LM7815 regulator (TO-220) was used instead of the little LM78L15 TO-92. I works just the same but takes up more room and cost.

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At right; detailed pictures of the vero board after parts soldered in place.

The copper breaks are scalloped out with a 5/32 drill bit with a rubber band wrapped around as a handle.

All the hookup wires are threaded through the board by just drilling 1/16th holes where convenient (without disrupting the circuit) and feeding the wire up from the underside to the appropriate hole. This makes for highly reliable wiring. If the wires are just directly soldered in from the top they easily fatigue and break off whilst assembling. Many of the track breaking scallops can be used for this dual purpose.

The parts list on a Word doc.

At right is the overall schematic including the Altronics / Jaycar kit and the power adaptor board from EA.

Note: There is a mistake on this circuit relating to what is 'HOT' and 'COLD'. The indication on the board of +ve or 'hot' is in fact -ve phase , or 'cold', so these need to be reversed when connecting the XLR & TRS output sockets.

At right is the wire up connection diagram for the DI. Click on the pic for the full res one.

The extra bits for -15dB pad are best put on a small board like the pictures at the bottom of this page.

Note: There is a mistake on this circuit relating to what is 'HOT' and 'COLD'. The indication on the board of +ve or 'hot' is in fact -ve phase , or 'cold', so these need to be reversed when connecting the XLR & TRS output sockets.

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At right: plans for the case which is an Altronics part number:

Diecast Aluminium Box With Flanges 222x146x55 IP66 H0429 $36.95

Front layout:

Rear layout

Left side layout:

Right side layout

The one pictured at right was built by a student in class.

The extra bits for -15dB pad are best put on a small board like the one indicated in the pictures at right.

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The one pictured at right was built by a student in class.

The extra bits for -15dB pad are best put on a small board like the one indicated in the pictures at right.

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