EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier

Dave reverse engineers the XuanZu X2-U808 Hi-Fi Headphone Amplifier to see if the valves actually do anything.
What is the circuit topology?
E180F (6J9) pentode valve datasheet: http://frank.pocnet.net/sheets/009/e/E180F.pdf
Doug Ford's Microphone design series: https://www.youtube.com/playlist?list=PLvOlSehNtuHv98KUcud260yJBRQngBKiw
Reverse Engineering How-To video: https://www.youtube.com/watch?v=lJVrTV_BeGg
Forum: http://www.eevblog.com/forum/blog/eevblog-837-reverse-engineering-a-valve-headphone-amplifier/

EEVblog Main Web Site: http://www.eevblog.com
The 2nd EEVblog Channel: http://www.youtube.com/EEVblog2

Support the EEVblog through Patreon!
http://www.patreon.com/eevblog

EEVblog Amazon Store (Dave gets a cut):
http://astore.amazon.com/eevblogstore-20

T-Shirts: http://teespring.com/stores/eevblog

Donations:
http://www.eevblog.com/donations/
Projects:
http://www.eevblog.com/projects/
Electronics Info Wiki:
http://www.eevblog.com/wiki/
💗 Likecoin – Coins for Likes: https://likecoin.pro/@eevblog/dil9/hcq3