Aelius

About the Aelius

The Ypsilon Aelius is a hybrid monoblock power amplifier that uses a single-ended class-A tube input stage transformer-coupled to a push-pull MOSFET output stage, implemented with only two gain stages and no overall feedback for high transparency and musicality. Its original design employed a NOS Siemens C3g pentode tube for the input stage with tube rectification (EZ81/6CA4), while later production has also supported alternative small-signal tubes depending on market and revision. The current Aelius specification is 200 W RMS into 8 ohms and 350 W RMS into 4 ohms, with approximately the first 60 W operating in pure class A before transitioning to class AB, providing substantial power and control for real-world loudspeakers while retaining single-ended-like purity. The amplifier uses an interstage transformer for phase splitting and low-impedance drive to the MOSFET output devices, preserving signal integrity and wide bandwidth. Published specifications list a bandwidth of 11 Hz-75 kHz (-3 dB), input impedance of 47 kohm, voltage gain of x30 (~29.5 dB), and output impedance around 0.25-0.4 ohm depending on revision and measurement. The Aelius chassis measures about 425 x 425 x 230 mm (W x D x H) and weighs roughly 45 kg (99 lb) per unit. It is equipped with balanced (XLR) and unbalanced (RCA) inputs, with a rear-panel switch to select input type, and includes a ground-lift switch to help minimize hum from ground loops in complex systems. Hand-built in Greece, the Aelius is widely described by reviewers and distributors as combining high power, transparency, dimensionality, and a spacious soundstage, and is positioned to drive virtually any high-quality loudspeaker while maintaining the refinement associated with Ypsilon's tube-based designs.