2 Watt Audio Amplifier

Designed for self-powered 8, 4 & 2 Ohm loudspeakers, Bass-boost switch

This amplifier was designed to be self-contained in a small
loudspeaker box. It can be feed by Walkman, Mini-Disc, iPod and CD
players, computers and similar devices fitted with line or headphone
output. Of course, in most cases you will have to make two boxes to
obtain stereo.

Circuit diagram:

2 Watt Audio Amplifier Circuit

2 Watt Audio Amplifier Circuit Diagram

P1 = 10K
R1 = 33K
R2 = 33K
R3 = 33R
R4 = 15K
R5 = 1K
R6 = 1K
R7 = 680R
R8 = 120R-1/2W
R9 = 100R-1/2W Trimmer Cermet
C1 = 10µF-63V
C2 = 10µF-63V
C3 = 100µF-25V
C4 = 470µF-25V
C5 = 47pF-63V
C7 = 470µF-25V
C6 = 220nF-63V
C8 = 1000µF-25V
D1 = 1N4148
Q1 = BC560C
Q2 = BC337
Q3 = TIP31A
Q4 = TIP32A
SW1 = SPST switch
SPKR = 3-5 Watt Loudspeaker

Circuit Operation
The circuit was deliberately designed using no ICs and in a rather
old-fashioned manner in order to obtain good harmonic distortion
behavior and to avoid hard to find components. The amplifier(s) can be
conveniently supplied by a 12V wall plug-in adapter. Closing SW1 a
bass-boost is provided but, at the same time, volume control must be
increased to compensate for power loss at higher frequencies. In use, R9
should be carefully adjusted to provide minimal audible signal
cross-over distortion consistent with minimal measured quiescent current
consumption; a good compromise is to set the quiescent current at about
10-15 mA. To measure this current, wire a DC current meter temporarily
in series with the collector of Q3.

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