power supply voltages. Referring again to Figure 1, the
positive supply is at the top and negative is at the bottom.
POWER SUPPLY
CONSIDERATIONS
Regulated power supplies are a totally unnecessary
complication in this project. A well designed amplifier
done with power supply rejection in mind doesn’t care
about precise power supply voltages. Power supply
rejection (the ability of the amplifier to ignore ripple
voltage and changes in supply voltages) is excellent in
these amplifiers. I tend to use perfboard for prototypes
(also referred to as Vector board for the name of the
manufacturer). The holes are at 0.1” centers which is
convenient for placing parts.
For this headset amplifier’s power supply, I suggest an
18 volt center-tapped transformer. The rectifiers (1N4001s)
are very inexpensive and widely available. The filter
capacitors can be found at several surplus places.
GETTING HOOKED UP
Output voltage will be about ± 12 volts — perhaps a
little higher with no load. Connect the ground ends of the
two filter capacitors very solidly and run a short bus off of
them. Connect the center tap of the transformer here. This
will be the “quality ground” for the amplifier.
The amplifier ground will connect to this point using
ordinary hookup wire. The headset ground return should
be to this point, as well. Headset wiring doesn’t need to
be anything special. Ordinary hookup wire will be fine.
Of course, you will want to connect a headset jack to
the output.
30 September 2013
Transistors
Q1-5 2N5551 NPN
Q6-9 2N5401 PNP
Q10-11 BD139
Resistors
All 1/4 watt 5% carbon film
Electrolytic capacitor
voltages as marked.
The 100 pF capacitor must
be mica or NPO ceramic.
■ FIGURE 2.
Amplifier schematic.
