Elenco 130-in-1 Electronics Playground - Manual (Page 92)

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This is another two-power source microphone
amplifier, but this one is an inverting amplifier. You
will use the earphone as a microphone again.
Slide the switch to position B and construct the
circuit. Once you finish the wiring, slide the switch to
position A to turn the power on, adjust the control
clockwise, and speak into the “microphone” – the
earphone. This project works just like the preceding
one.
IC 2 is an inverting amplifier and IC 1 is used as a
buffer between the earphone and IC2, and has a
gain of 1. IC2 is an inverting amplifier, with the input
applied through its negative (–) terminal, not the
positive (+) one as in our last project. IC2’s gain is
about 100, as determined by:
R1/R2 = 100k/1k=100.
If you increase R1 or decrease R2, the gain becomes
larger. See what occurs to the gain when you alter
the value of R2 to 470.
Notes:
EXPERIMENT #73: INVERTING DUAL SUPPLY OP AMP
Wiring Sequence:
1-29
2-30
3-64-90
27-69
63-131
65-89-76
68-67-75
70-134
121-135
122-132
124-119-26-66-5-14-EARPHONE
28-13-EARPHONE
Schematic