Elenco Electronics EP-130 - Sine Wave Oscillator with Low Distortion

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151
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In this experiment, you build and study a low-distortio
n
sine wave oscillator. Build this experiment after you
h
ave
b
u
il
t an
d
stu
di
e
d
t
h
e prev
i
ous exper
i
men
t
b
ecause this one has no transformer; transformer
s
are likely to cause distortion because of their non-
linear characteristics.
A
s
i
n t
h
e prev
i
ous exper
i
ment, you s
h
ou
ld
li
sten to t
he
tone o
f
this oscillator and modi
f
y the control
f
or the
clearest-soundin
g
sin
g
le tone (the one with the least
distortion
)
. Again, start with the control nea
r
maximum. The operatin
g
f
requency is about 300Hz a
t
the minimum distortion setting o
f
the control.
We call this circuit an RC phase shift oscillator, and i
t
i
s cons
id
ere
d
a
b
as
i
c s
i
ne wave osc
ill
ator.
Th
e pos
i
t
i
v
e
f
eedback o
f
the signal causes oscillations to occur.
The resistors (R) and capacitors (C) make up the path
for the si
g
nal to the transistor base. Every time th
e
signals pass the R
C
circuits, a slight time lag occurs
.
In other words, the rise and fall of the wave
(
th
e
p
hase) shifts sli
g
htly. That’s why we call it phase shift
.
A
f
ter the signal has traveled through the circuit, th
e
p
hase shi
f
ts 180 degrees. When the collector voltage
rises
,
this rise is
f
ed back to the collector with th
e
p
hase shi
f
ted. When the base voltage rises, the
collector volta
g
e falls. This repeatin
g
cycle causes th
e
trans
i
stor to osc
ill
ate
.
The frequency changes when you change the control
setting, because the degrees o
f
phase shi
f
t changes.
The tonal quality also chan
g
es. Set the control to the
p
oint where you can hear the purest tone; at this point
a clear sine wave is
g
enerated.
No
t
es
:
EXPERIMENT #12
9
:
S
INE WAVE
OSC
ILLAT
O
R WITH L
O
W DI
S
T
O
RTI
ON
Wiring Sequence:

124-27-48-82-80-EARPHONE

47-105-93-77-EARPHONE

81-109-108-28

94-110-46

78-138

79-106-107

119-137

121-122
S
chematic