My Circuit (First Edition)
Describing the Main Control Side
Side Note: The capacitor connected to AO and AIN is removed due to me receiving no improvement on audio out (AO). The capacitor was most likely intended to be a smaller value, but I decided to remove it entirely. Also, the LED on LAMPB, in my case, is used as an indicator if there is sound coming through. The LED lights up whenever there is a signal coming from the microphone. The louder the signal, the brighter the LED will be. The LED also starts out lighted up once power is turned on but will grow brighter with more noise.
Background to Control Pins
ROB: The robot pin activates the robotic voice effect. This changes your voice to sound flat, monotone, and synthetic.
VIB: The vibrato effect modulates the pitch slightly up and down.
FVIB: This is the frequency vibrato control. By connecting a potentiometer between FVIB and VSS, you can control how fast the vibrato oscillates.
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If SW0~SW2 are all high, TGU and TGD can shift the frequency through 7 steps. So for my circuit, I removed the switches as I am utilizing push buttons, and SW0~SW2 are by default set to high. TGU stands for "Tone Go Up" and TGD stands for "Tone Go Down".
Describing the Audio Amplification Side
I am using an external PAM8403 Mini 2 Channel 3W Stereo Class D Audio Power Amplifier to boost the microphone signal.
I connected a 10kΩ potentiometer in series with AUDIO and INL for volume control. Since not in use, according to the datasheet, INR must be tied to ground, and a resistor must be placed on OUT_R.
I am utilizing the PAM8403 audio amplifier because it provides 80-85% efficiency with 3W output power and can operate from 2.5V to 5.5V. Comparing this to the other audio amplifiers, the LM386 provides ~25% to 30% efficiency with an operating voltage of 4V-12V (commonly 9V), and the TDA2822 provides ~35% efficiency with an operating voltage of 3V–15V