Mini Class A Audio Amplifier

Posted on Aug 8, 2012

The philosophy behind this minimalist design has been explained by Flavio Dellepiane on his highly interesting site 1. I have myself written an article about this fleapower amp from Italy in the American magazine AudioXpress 2. All relevant details are published there. A single channel of the amplifier can be built for only a few Euros, especially if you have a well-stocked junkbox. I used a regulated power supply to feed the two amplifier channels, Q6 is mounted on a heatsink. The power transformer comes from a damaged TEAC amplifier. It has a secondary voltage of 60V with a center tap. D1 and D2 are fast recovery diodes, e.g. MUR860. It is a good idea to bypass C7,C10 and C11 with smaller MKT or MKP capacitors.

Mini Class A Audio Amplifier
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The sound of this amplifier is very good for such a simple design, lively and threedimensional. No cross-over hardness or other transistor nasties. However, don’t push it too hard for then you will begin to hear harmonic distortion. Singers will sound as if they keep both their hands, like a cup, in front of their mouth. If this happens, reduce the volume (or use speakers with a greater efficiency). P1: 47k log potmeter (separate for each channel) R1: 100k R2: 12k R3: 47k R4: 8k2 R5: 1k5 (optional) R6: 2k7 R7,R9: 100 Ohm R8: 560 Ohm R10: 1 Ohm 3W (all resistors ½ W unless otherwise indicated) (R5 and C5 are an optional bass-boost facility) (these parts can be omitted, I did not use them) C1,C2: 10µF 63V (I omitted C1 and I used a MKT cap for C2) C3: 47µF 25V C4: 100µF 35V C5: 150nF 63V MKT or MKP (optional) C6,C7: 220µF 25V C8: 1000µF 25V Q1: BC560C (I used a 2SA970) Q2,Q3: BD439 Sizable heatsink capable of dissipating 17 Watts continuously

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