Elenco Electronics EP-130 - Twin-T Oscillator

-
152
-
The twin-T type audio oscillator is very popular fo
r
use with electronic or
g
ans and electronic tes
t
equipment because it is very stable
.
Th
e res
i
stors an
d
capac
i
tors
i
n t
h
e tw
i
n-
T
networ
k
determine the frequency of oscillation. The letter T is
used because the resistors and ca
p
acitors ar
e
arranged in the shape of the letter T in the schemati
c
dia
g
ram. There are two T networks in parallel acros
s
f
rom each other
;
hence the term twin is used. The
capacitors in series shi
f
t the phase o
f
the wave; th
e
resistors in series supply volta
g
e to the transistor’
s
base as well as shi
f
tin
g
the phase o
f
the wave
.
Carefully adjust the circuit to obtain pure sine wav
e
output as in the previous two projects. Modi
f
y th
e
contro
l
very s
l
ow
l
y over
i
ts ent
i
re ran
g
e unt
il
you
h
ea
r
a tone
i
n t
h
e earp
h
one t
h
at
i
s very
l
ow an
d
resem
bl
e
s
the lowest note of a lar
g
e pipe or
g
an. This control
setting should be between 7 and 10 on your dial.
O
nce the oscillation has started, ad
j
ust the contro
l
care
f
ully
f
or the settin
g
that
g
ives the purest soundin
g
low note near the high end o
f
the dial
.
Y
ou can exper
i
ment w
i
t
h
t
hi
s c
i
rcu
i
t
i
n many ways.
We
suggest you try di
ff
erent values
f
or the 10k
Ω
an
d
4
7
0
Ω res
i
stors, an
d
try us
i
ng
hi
g
h
er an
d
l
ower
b
atter
y
voltages. Also, if you have a VOM, try measurin
g
ci
rcu
i
t vo
l
tages
.
No
t
es
:
EXPERIMENT #1
30
TWIN-T
OSC
ILLAT
OR
Schematic
W
iring Sequence:

7
2
-
106
-
116
-
2
7-
124

28-104-102

46
-
103
-
8
7

4
7-101-86-81-EARPHONE

48
-7
1

119-115-82-EARPHON
E

85
-
88
-1
05

121-122