A Voice Changer Implemented With Analog Electronics

 

The End-All, Be-All, of Voice Modulation  An in-depth look into audio manipulation

 

Problem How can we recreate the sense of nostalgia that we feel when we think of the voice changer toys we had as children? How can we resurrect the joy of childhood? How can we receive a passing grade in PHYS 3330?

 

The Circuit 5 Sections ● Electret Condenser Microphone/Auxiliary Input

● ● ● ●

Non-Inverting Amplifier Ring Modulator Choppy Effect Push Pull Transistors

 

Electret Condenser Microphone

 

Non-inverting Op Amp Stage 1

Stage 2

 

Theory G = 1 + (Rf  / R) Stage 1

Stage 2

G1 = 1 + (10kΩ pot / 1kΩ)  G1 = 11 - 1

G2 = 1 + (1kΩ / 1kΩ)   G2 = 2

Total Gain = G1×G2 = 22 - 2

 

Model

G = Vout / Vin

G = Vout / Vin

G = 11.3V / 0.561 V = 21.899 Well within 5% of theory!

G = 1.12V / 0.504 V = 2.222 Well within 15% of theory!

 

Ring Modulator

 

Effect

 

Model f output = f input × f carrier Output Signal

Sine Wave over a Triangle Wave

 

Test

Output

Input

Carrier

 

Parts BAT 48 Schottky Diodes ● Low forward voltage drop (0.150.45 volts)

42TM018-RC Transformers ● Specific for audio

 

555 Timer Controlled MOSFET Switch

 

Theory vs. Experiment

1=RBC×ln(2) T T2=(R A+RB)C×ln(2) T=T1+T2 f=1/T

Duty Cycle = T2/(T1+T2)

 

49.9 kΩ resistor for R B

Theory: T1=(49.9 kΩ)(2.2 μF)ln(2)=0.076 s  T2=(47 kΩ+49.9 kΩ)C×ln(2)=0.148 s T=T1+T2=0.223 s f=1/T=4.46 Hz Duty Cycle = T2/(T1+T2) = 66.1% Measured: T1=0.080 s T2=(47 kΩ+49.9 kΩ)C×ln(2)=0.156 s T=0.236 s f=1/T=4.24 Hz Duty Cycle = T2/(T1+T2) = 66.1% Well within 5% of theory!

 

100 kΩ resistor for RB

Theory: T1=(100 kΩ)(2.2 μF)ln(2)=0.152 s  T2=(47 kΩ+100 kΩ)C×ln(2)=0.224 s T=T1+T2=0.376 s f=1/T=2.65 Hz Duty Cycle = T2/(T1+T2) = 59.6% Measured: T1=0.160 s T2=(47 kΩ+49.9 kΩ)C×ln(2)=0.240 s T=0.400 s f=1/T=2.50 Hz Duty Cycle = T2/(T1+T2) = 60.0% Within 10% of theory!

 

Wire for RB (effectively zero ohms)

 

Theory: T1=(0 Ω)(2.2 μF)ln(2)=0 s  Duty Cycle=T2/(T1+T2)=T2/T2=100% Measured: Duty Cycle = 100%

 

Push-Pull Output Parts used: NPN: 2N4922 NPN:  2N4922 PNP: 2N4919 PNP:  2N4919 Power Rating: 30 Watts!!!!

Image Credit: http://upload.wikimedia.org/wikipedia/en/1/1e/Pushpull.PNG http://upload.wikimedia.org/wikipedia/en/1/1e/Pushpull.PNG