Doobooloo designed and built his balanced portable Doobooloo amp way back in 2008. The thread is dated November 1st, 2008, much earlier than Ray Samuel’s Protector. Some may argue that it’s not a 100% percent portable, as it still requires power from an external PSU unit, but I’m not here to put fire over the debate. 🙂
Anyway, I received this amplifier yesterday. It’s a very nice built. Very clean and professional build, especially if you consider it’s a DIY project. I’m impressed at how clean the PCB layout and soldering work is. It’s a pity that doobooloo never made the PCB available to the general public. I believe that he made several PCBs, but after those are gone, he never made any more. People were dying to get a hold of the PCBs, since at the time, it was the smallest balanced amplifier that you can find.
It takes both a 3.5mm and RCA input. Convenient for hooking up to a desktop source or from a DAP. I don’t think you want to plug both sources in at the same time, as there is no input selector. Output is through two TRS (aka 1/4″ jack), meaning that you need to recable your balanced cans to dual TRS jacks, or build an adapter.
What’s interesting is that the TRS jacks serve a dual purpose for feeding single ended cans too. The left TRS is marked (+), and you can plug in a single ended headphone there. The left TRS is marked (-), and likewise you can plug in a single ended headphone, but reversed in polarity. I’ve made the proper TRS to XLR conversion adapter, so I can use my balanced HD800 with it.