• on Audio/Video/Photography
  • Published in issue 10/2003 on page 0
About the article

Valve headphone Amplifier

EL84 (6BQ5) at an anode voltage of 40 V

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.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Resistors:
R1,R3,R5,R7 = 1k?
R2,R6 = 100?
R4,R8 = 220k?
P1 = 100k? 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
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