• on Audio/Video/Photography
  • Published in issue 7/2006 on page 0
About the article

Simple Hybrid Amp


Simple Hybrid Amp
The debate still goes on as to which are better, valves or transistors. We don't intend to get involved in that argument here. But if you can't make your mind up, you should try out this simple amplifier.
This amplifier uses a valve as a pre-amplifier and a MOSFET in the output stage. The strong negative feedback makes the frequency response as flat as a pancake.
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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.

R1 = 1M?
R2,R4 = 180
R3 = 2k2
R5 = 1k
R6,R7 = 100k
R8, R9 = 4k7
R10 = 47k
R11,R12,R13 = 1.5 5W
P1,P2 = 4k7 preset
C1 = 100nF 250V MKT, lead pitch 15mm, dim. 7x18 mm max.
C2 = 220pF
C3 = 10µF 400V radial, lead pitch 5 mm o 13mm max.
C4 = 2µF2 250V, lead pitch 27.5 mm, dim. 11x30 mm max.
C5,C10 = 100nF
C6 = 100µF 25V radial
C7 = 2µF2, lead pitch 5 or 7.5mm
C8,C9 = 4700µF 25V radial, lead pitch 7.5mm, o 18mm max.
L1 = ? 50 mH, not on board, see text
D1,D2 = 1N4001
T1 = BC337
T2 = BUZ11 (or IRFZ34N)
V1 = ECC88 with 9-pin valve socket (Chelmer Valve Company)
Heatsink for T2, ?1 K/W
PCB, ref. 050153-1 from The PCBShop
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