About the article

Improved Hybrid HeadPhone Amplifier

Improved Hybrid HeadPhone Amplifier
Jeff Macaulay’s excellent single valve ECC82/12AU7 'Hybrid Headphone Amp' (HHA) published in spurred the author to implement some modifications culminating mainly in an additional input preamp. The resulting project was then slightly reworked In the Elektor Audio Labs and the result is shown here, along with a PCB design to Elektor standards.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD 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


Voltages measured w.r.t. circuit ground
T1/T6 base 0.7 V
T2/T7 base 1.4 V
T3/T8 base 3.8 V
T3/T8 Emitter 2.8 V
ECC82 grid 4 V
T10/T12 Emitter 6.2 V
T9/T11Base 0.67 V
ECC82 anodes 10 V
ECC82 pin 5 9.4 V
D2 (across device) 0.8 V
T5 VCE 1.3 V
R6/R14 (across device) 6.85 V

Component list

R1,R8,R9,R15 = 10k?

R2,R4,R10,R12 = 91k? (E96: 90k?9)

R3,R11 = 15k?

R5,R13 = 22?

R6,R14,R16,R17,R22,R23 = 1k?

R7 = 39k?

R18,R21,R24,R27 = 560?

R19,R25 = 33k?

R20,R26 = 8k?06


C1,C6 = 2?F2 100V, lead pitch 22.5mm (WxL = 10 x 26 mm abs. max.)

C10,C12 = 10?F 63V, lead pitch 22.5mm (WxL = 10 x 26 mm abs. max.)

C2,C7 = 100nF, MKT, lead pitch 5mm or 7.5mm

C3,C8,C11,C13 = 100?F 25V, lead pitch 2.5mm, diam. 8.5 mm max.

C4,C9 = 2200?F 25V, lead pitch 7.5mm, diam. 18mm max.

C5 = 1000 ?F 25V, lead pitch 5mm, diam. 10 mm max.


D1,D3 = red LED

D2 = 1N4004

T1,T2,T6,T7,T9,T10,T11,T12 = BC550C

T3,T5,T8 = BC517

T4 = BD139


V1 = ECC82 or 12AU7

9-pin (‘Noval’) PCB mount socket, e.g. Conrad Electronics # 120529

PCB, # 080310-1 from www.thepcbshop.com

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