Elenco Electronics EP-130, Руководство пользователя

Страница: 34 / 160

-34-
This circuit is a strong two-transistor amplifier. An
amplifier uses a small signal to control or produce a
large signal. This amplifier is similar to an early
model transistor hearing aid amplifier. The speaker
acts as a dynamic microphone.
Using your VOM on this amplifier to measure circuit
voltages will help you learn how transistors work.
The measured voltages will help you determine
current measurements and the way this circuit
works.
Your kit’s speaker can change sound pressure into
weak voltages. The transformer increases the
voltage somewhat. This voltage is then applied to
the NPN transistor through the 3.3
μ
F capacitor.
The amplifier voltage at the output of the NPN
transistor is coupled into the PNP transistor through
the 0.1
μ
F capacitor. It is further amplified by the
PNP, and is coupled to the earphone through the
100
μ
F capacitor.
It’s about time to talk about the transformer. The
transformer has a copper wire wound hundreds of
turns. We call it a coil. A transformer has two coils
separated by a plate.
When electricity flows through a coil, it creates a
magnetic field. The reverse is also true – if a coil is
subjected to a change in its magnetic field strength,
electricity flows through it. So, when electricity flows
through the first (or primary as we often call it) coil
of a transformer, the magnetic field created by the
number of windings of each coil is different, so the
voltage of the electricity for each coil is also
different.
This establishment of an electric charge using a
magnetic field is called induction. Go back to Project
15 (Capacitor Discharge / High Voltage Generator)
and recall how large voltage is induced at the
secondary side when 9V is applied by the primary
side of the transformer.
Notes:
EXPERIMENT #21: SOUND AMPLIFIER
Wiring Sequence:
o
1-29
o
2-30
o
3-112
o
5-124-48-116-102-78-13-EARPHONE
o
93-109-40
o
41-94-77-14-EARPHONE
o
42-72
o
91-100-101-111-46
o
75-92-99-110-47
o
71-76-115-119
o
121-122
Schematic