OPA2134 CMoy Style Portable Headphone Amplifier

This simple headphone amplifier is based on the high performance OPA2134 opamp chip. This headphone amp\driver is good sounding and portable. The schematic is based on the very popular CMoy headphone amp design with some changes in passive parts values. For the power supply I elected to power the amp from two 9V batteries (18V) which provides longer playback time and greater dynamics.

There is only 100 mm of hookup wire in the signal path and all connections are component-2-component on the protoboard. Low ESR 200uF caps and a resistive network provide the differential voltages required to operate the chip without an output capacitor. The brd. is silver soldered with Mil. spec machined chip socket and Russian PIO caps on the input. Power only comes on when both phone jacks have plugs in them and the power switch (at the back) is on. The enclosure is impact resistant and lined with heavy aluminum foil for shielding and enclosure resonance control. The sound is clean and bright with good volume and dynamics. The amp is dead quiet with no signal.