So I've spent the evening building the active DI box from the end of this page: http://sound.westhost.com/project35.htm . As I don't have any bipolar electrolytic caps, I've made it only battery powered for now, with appropriately oriented regular electrolytics for the output decoupling.
I also added a buffered 1/4" output, by just slapping a 1kiloohm resistor and 10uF capacitor on the output of the unity gain non-inverting opamp. The opamp I used is a TLC272CP.
My problem is when I hookup a mic cable to the balanced XLR output, it goes crazy with noise all over (and it bleeds through to the regular output too). It does it even if it isn't plugged in at the other end so its not a ground loop. I also hooked up a guitar cable through an 1/4"->XLR converter and the same thing happen. If I don't hook up anything to the XLR output, the 1/4" output works fine on its own.
I hooked up my scope and it seems to be a constant oscillation in the 500khzish area, 700mV amplitude, it jumps around a bit if you touch the circuit board.
It's late now and can't be bothered to go in for another round of soldering. But does this sound like capacitive loading on the opamp? The are the 100ohm resistors too small (as the output with the 1000ohm resistor functions ok)? Or is there just something funky about the opamp I used?
So, the followup: I swapped the TLC272CP for a TL072 and it now work fine. May be this a heads up to anyone ever working with one of these.
> The opamp I used is a TLC272CP.
That's a 16V max chip. Rod's plan applies 24V.
Dunno if that was the problem, but....
INFO:
the link in the OP no longer lives, but here is its other location:
https://sound-au.com/project35.htm
(https://i.postimg.cc/nCxgFP0t/arise.png) (https://postimg.cc/nCxgFP0t)