Class A tube amplifier with 24-Bit 384K USB DAC. Version with tube power supply. The Woo Audio WA7 "Fireflies" Amp/DAC is a combination of a high-performance headphone amplifier and an integrated USB DAC. It features a pure tube design with 6C45 tubes in Class A, a single-ended topology, and transformer-coupled outputs. No semiconductors have been used throughout the amplification path. The D/A converter is designed for sampling rates of up to 24 Bit/384 K, ensuring pure data integrity transmitted via a standard high-speed USB 2.0 interface in asynchronous mode. High-quality design elements include a pair of output transformers with nickel cores, a screwless aluminum chassis that is visible from any angle, a remote-controlled linear external power supply for the amplification circuit, a custom-made toroidal transformer, and military-grade multilayer circuit boards. A dedicated connector for in-ear monitors features comprehensive volume controls to minimize noise. Despite its extremely compact size, the Fireflies are a true powerhouse capable of driving almost any demanding audiophile headphone. Fireflies can also be used as a standalone DA converter to meet various system deployment requirements.