The Meier Audio Corda Opera is the first amplifier with a balanced headphone ground, offering many of the advantages of a true balanced headphone setup without the need of balanced connections.
The OPERA does not keep the signal of the ground wires fixed but adds an extra signal to all the four wires (signal wires and ground wires) such that the sum of the voltages of the 4 wires is constantly zero. This extra signal is the same for all wires so the voltage differences between the two wires of a single driver do not change. The effective audio signal is still the same.
The OPERA has two headphone-sockets, one with a very low output impedance and one with 120 Ohm output impedance. This allows to optimize the driving characteristics for the headphone used.
The amplification section is build around LM6171 opamps biased into class-A. For the output stages BUF634 buffer amplifiers are used. The amp is DC-coupled and any capacitors found in the signal path are of the highest quality polypropylen and polystyrol.
An extra feature of the OPERA is a high quality built-in DAC. Digital data are accepted through the coaxial S/PDIF input or through the USB-port that can be easily connected to any computers system.
The digital receiver section is based on the CS8420 receiver chip and provides effective jitter reduction at all frequencies above 1 kHz. Of course digital input signals are decoupled using a pulse transformer to minimize any adverse interferences coming from the digital source.
The DA-conversion section is based on the Burr-Brown PCM1794. The I-V conversion is performed by a non-standard circuitry of our own design based on the LM6171 opamp (of course biased into class-A for maximum sound quality).
It is impossible to think of a CORDA amplifier without crossfeed filter. A crossfeed filter simulaties aspects of the natural hearing process to reduce this stress and to make headphone listening more relaxing.