• on Audio/Video/Photography
  • Published in issue 9/2003 on page 0
About the article

Valve Preamplifier (1)

Classic technology revisited

Valve Preamplifier (1)
This stereo preamplifier is primarily intended to be used as a companion to the Valve Final Amplifier described in the April and May 2003 issues, but it can easily be used with other power amplifiers as well. The circuit has all the usual controls and input options, and it is relatively easy to build, even if you’re not a valve guru.Like most preamplifiers, this one has controls for volume, tone (treble and bass) and balance. The input options also correspond to the usual scheme, the only exception being that this preamplifier has a phono input — which can no longer be taken for granted these days.
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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.

Extra info, Update
In the Components List for the Power Supply board, the lead pitch of capacitor C13 should be amended to read: 15 mm.
Amplifier board
Resistors:
R1 = 680k?
R2,R12 = 150k?
R3 = 68k?
R4,R9,R17 = 2k?2
R5,R11 = 100k?
R6 = 390k?
R7 = 10M?
R8,R19 = 10k?
R10 = 0? (wire link, see text)
R13 = 15k?
R14,R16,R20 = 47k?
R15 = 1k?2
R18 = 1k?5
R21 = 1k?
All resistors: metal film 0.5-1W, e.g., Beyschlag MBE-0414
P1,P2,P4 = 500k? logarithmic, stereo
P3 = 20k? preset, horizontal, lead pitch
5.08/2.54mm (Conrad Electronics # 424420) or 5/10mm
P5 = 50k? logarithmic
Capacitors:
C1 = 100pF 250V polypropylene, e.g. Conrad Electronics # 458686
C2 = 330pF 250V polypropylene, e.g., Conrad Electronics # 458740
C3 = 10µF 385V, axial, 12x30 mm
C4,C10 = 15nF 630V, lead pitch 10mm
C5,C14,C17 = 220µF 35V, radial, lead pitch 5mm
C6 = 2µF2 250V, lead pitch 27.5mm or 22.5mm
C7,C12 = 100nF 400V, lead pitch 15mm
C8 = 4nF7 630V, lead pitch 10mm or 7.5mm
C9 = 270pF 250V polypropylene, e.g., Conrad Electronics # 458732
C11 = 1nF 630V, lead pitch 10mm or 7.5mm
C13 = 22µF 350V, axial, 16x36 mm
C15 = 1µF 250V, lead pitch 22.5mm
C16 = 10µF 35V tantalum, lead pitch 2.5mm
Valves:
V1 = EF86, 6267 or CV2901
V2 = ECC82, E82CC or12AU7
Semiconductors:
T1 = BF245A
D1 = 1N4148
Miscellaneous:
Re1 = DIL relay, 1x changeover, 12V coil.
2 Noval (9-pin) valve sockets, PCB mount, pin
circle 18mm, e.g., Conrad Electronics # 120529.
IC socket, 14-way, turned pins (for Re1).
36-way pinheader, straight.
36-way socket, straight.
4 PCB solder pins with mating sockets.
PCB, order code 020383-1
I/O board
Resistors:
R1-R4, R6-R9 = 100k?
R5,R10 = 20k?
Capacitors:
Cx,Cy = 2µF2 MKT (metallised plastic) (see text)
Semiconductors:
D1-D8 = 1N4148
Miscellaneous:
Re1-Re8 = SI relay, 1 make
contact, 12V coil, e.g., Conrad Electronics # 504602.
14 cinch chassis sockets.
SIL PCB header, 5-way.
6 solder pins with mating sockets.
PCB, order code 020383-3
Power supply bo
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