I have a first generation Digidesign Mbox and I'm looking for some help from anyone who has experience with these and is familiar with the control circuits. I have done the Zach Poff mod that allows it to be used as a standalone pre-amp. U23 pin 16 has a jumper to the via next to pin 12 and the trace to pin 12 is cut.
From Zach Poff's website detailing the mod
Explanation: Pin 12 of the HEF4094 drives the “enable” pin of several MIC5205 voltage regulators which power the audio circuits. When you plug in the Mbox, the microprocessor tells the HEF4094 to keep pin 12 grounded (audio circuits disabled) until the computer grants permission for full power. Then the HEF4094 brings pin 12 high and audio turns on. Our jumper replaces this logic, forcing pin 12 high all the time so audio is always on.
It works great, except the phantom power is only +5V. I'm wondering if there's maybe a logic control to activate a regulator, or DC-DC step-up converter for the +48V rail. I don't have schematics, so I'm not sure where the +48V rail comes from. I suppose it's possible that the IC for the +48V rail is just bad. I'm powering the Mbox from an old Apple 1A +5V USB supply. When I power the Mbox off a computer's USB bus, the phantom power is still only around +5V.
From Zach Poff's website detailing the mod
Explanation: Pin 12 of the HEF4094 drives the “enable” pin of several MIC5205 voltage regulators which power the audio circuits. When you plug in the Mbox, the microprocessor tells the HEF4094 to keep pin 12 grounded (audio circuits disabled) until the computer grants permission for full power. Then the HEF4094 brings pin 12 high and audio turns on. Our jumper replaces this logic, forcing pin 12 high all the time so audio is always on.
It works great, except the phantom power is only +5V. I'm wondering if there's maybe a logic control to activate a regulator, or DC-DC step-up converter for the +48V rail. I don't have schematics, so I'm not sure where the +48V rail comes from. I suppose it's possible that the IC for the +48V rail is just bad. I'm powering the Mbox from an old Apple 1A +5V USB supply. When I power the Mbox off a computer's USB bus, the phantom power is still only around +5V.
I mistakenly put the jumper from U23 pin 16 to pin 12 and it is supposed to go from pin 16 to the via that connects pin 12 to the circuit and then the trace to pin 12 is cut. I did cut the trace, but I had the jumper soldered to the incorrect side of the cut. Now that I relocated the jumper to the via, it is powering up in full-power mode and the +48VDC rail is active.
