The EB-703/258 is a high quality power supply and low-noise All-FET +48V Phantom regulator on one 150x40mm PCB. The regulator is capable of supplying 6 condenser microphones. The regulator is a discrete All-FET opamp. The differential input stage consists of the dual JFET Q1 and the cascode Mosfets Q2/Q3. The input FETs are operated at 2mA each. The second stage is also a Mosfet, operating at approx. 5mA. The output stage, a TO-220 Mosfet, operates as a source follower and is capable of delivering 100 mA. Q5 has to be heatsinked. The regulator is getting its reference voltage from D6, a low-noise buried zener reference diode. The diode is fed from D5, a 2mA FET constant current source.

The power supply needs 42V AC at 100mA to produce +55V unregulated DC for the regulator. The EB-703/258 can be mounted in the same case as the microphone preamps. However, it is recommended to mount the mains transformer in a separate case for maximum signal integrity.