I created hybrid headphone amp using op-amp & electron tube. (quite unique!)
see http://www.fa-schmidt.de/YAHA for details.
Most of parts are bought from mouser.com and digikey.com.
Capacitor: Nichicon Muse KZ
Op-amp: TI OPA2134P
Resistors: Dale
Case: Hammond Steel Instrument (1454 Series)
The schematic. I changed some parameters from the original.
The board.
I bought 2 electron tubes from tubedepot.com, electro-harmonix 6922 and Sylvania Jan 6922 (deadstock made in 1972). electro-harmnix tube is less noisy. People say this amp produces a lot of distortion but I think this amp creates better sound than the original iPod touch. Especially the low sound is much better than iPod touch.
Im sartisfied with this headphone amp. It sounds nicely! Also the orange light from the tube makes me relaxed!
