Part number: 12 Haos Redro Last update: 19/07/2009

Mono headphone amplifier module

Resources:

19 Overall schematic FIG | PDF
20 PCB layout FIG | PDF (copper) | PDF (copper+component)

Description:

A single channel headphone amplifier module suitable for driving headphones of 32 ohms or greater impedance. The amplifier is essentially a TL071 operational amplifier with an additional output buffer stage built from a complementary transistor pair.

Table 1: Component function

R1,2 These set the gain of the amplifier. The voltage gain is given by R1/R2.
R3,4 Biasing resistors. These allow a small bias current to flow into the bases of T1 and T2, so that both transistors are in a conducting state.
R5,6 Loading resistors. These prevent excessive current from flowing to the output, or between the supply rails.
C1 Reduces the gain at very high frequencies. Sometimes required for stability.
C2,3 AC bypass for D1 and D2.
C4,5 Low frequency supply decoupling capacitors.
C6,7 High frequency supply decoupling capacitors.
D1,2 Biasing diodes. The forward voltage drop of these diodes keep the base-emitter junctions of T1 and T2 forward biased so that they are conducting with zero input signal. This reduces the crossover distortion of the amplifier.
T1,T2 Discreet transistor buffer for IC1.

PCB layout:

The PCB is 47mm long and 27.5mm wide and uses a single-sided layout. The connectors are aligned along the bottom edge of the board to allow vertical mounting to a motherboard.

Power and cooling:

The module will dissipate up to 1.7W of power in normal operation with a ±15V supply. It is possible to cause overheating with a sufficiently large input signal and/or a an output short-circuit. The output should be limited to 5V RMS to remain within a safe operating area.

Images:


Completed module
Copyright © 2009 Taiyo Rawle. This document is released under the terms of the TAPR Open Hardware License version 1.0 or at your option any later version as published by TAPR: http://www.tapr.org/ohl.html