Sennheiser HD820 Closed-Back Headphones Pre-Owned Quasi mono directly heated double-diode

Quasi mono directly heated double-diode valve-rectified B+ power supply

and the result is a DAC that sounds like music rather than a convincing reproduction of it

Triangle Borea BR03 Connect active speaker

open-back Transducer type Dynamic Driver diameter 53mm Housing Honeycomb aluminum with magnesium frame Frequency response 5 Hz - 30 kHz Sensitivity 100 dB / mW Impedance 38 ohms Weight 235g (without cable) What Reviewers Say

using Kovar lead-wire with matched thermal expansion coefficient to eliminate vacuum leakage

Sennheiser HD820 Closed-Back Headphones Pre-Owned Quasi mono directly heated double-diodeSennheiser's flagship closed back headphone, the HD 820 uses Gorilla Glass ear cup covers with a concave design borrowed from reflector telescope technology to redirect sound reflections away from the driver. The result is a closed back headphone that sounds unlike any other. Type and Technology Over ear, closed back, dynamic. 56mm ring radiator transducer derived directly from the HD 800S, with concave Gorilla Glass ear cup covers that manage