Valve headphone Amplifier

It is not just power amplifiers that can deliver the much sought-after warmth of the ‘valve sound’ — headphone amplifiers can too. What is special about this project is that it is achieved using a safe anode voltage of just 40 V.Heated debates rage over whether, and how, a valve amplifier sounds different from (or perhaps better than) a modern semiconductor amplifier. There certainly are reasons why a valve amplifier might sound different. First there is the particular form of the characteristic curve (Ia plotted against Ug), whose gentle curve inevitably gives rise to increased distortion as the drive level is increased, especially when negative feedback is not employed.

Resistors:
R1,R3,R5,R7 = 1kΩ
R2,R6 = 100Ω
R4,R8 = 220kΩ
P1 = 100kΩ stereo logarithmic
potentiometer
Capacitors:
C1,C2 = 100nF
C3,C5 = 100µF 10V radial
C4,C6 = 10µF 63V radial
C7 = 100µF 63V radial
Valves:
B1,B2 = EL84 or 6BQ5 with noval socket (18mm diam.)
Inductors:
L1,L2 = 330mH choke (Toko 10RBH 239LY334K)
Miscellaneous:
JP1-JP4 = 2-way pinheader with jumper
K1 = 3-way PCB terminal block, 5mm lead pitch
K= 2- way PCB terminal block, 5mm lead pitch
TR1,TR2 = mains transformer 18V/4.8VA (Gerth # 421.18)
PCBs, order code 030064-1 and 030064-2