FET DI: Impedance converter...

[Gus]

Look at R6 and R8 what is the DC voltage drop across them.  The voltage drop across R11 gives the current draw of the complete circuit with voltage / resistance.  What supply voltage did you use for testing? 

One way to use this might be with a DC to DC converter you will need to figure out the power used by the circuit and if phantom can supply enough power.

 

[3nity]

you're right 48v might not supply enough.
i tested with +24V...

 

[3nity]

2sk170GR wich i'm using calls a drain current for 6.2ma max... the BL type on the schem calls for a 12mA max...

 

[JPK]

The circuit pulls around 5mA from a 24V supply. No problem for a phantom 48V. But the 2SK170 won't like it, too much voltage. You could insert a 20V zener serially with the 48V, that will reduce the voltage to 48-20=28V (cathode towards +48V).
Remember that this circuit is designed for driving a mic input. It has a -20dB attenuator that will bring an instrument signal down to a microphone level.