I. The Tone Circuit
The first Op-Amp acts as the Tone circuit by implementing a bandpass filter.
R1/R11 and R2/R3 are the potentiometers that change the cutoff freq of the bandpass filter
Bass Parameters:
Active Frequency: 50 - 500Hz
High Pass: 50 Hz
R1 = 1000Ω
C1 = 3.18uF
Low Pass: 500Hz
R2 = 1000Ω
C2 = 0.318uF
Treble Parameters:
Freq: 1000 - 2000Hz
High Pass: 1000Hz
R1 = 100Ω
C1 = 3.18u
Low Pass: 2000Hz
R2 = 250Ω
C2 = 0.318uF
II. The Distortion Circuit
The second Op-Amp is needed for the characteristic Distortion sound of the guitar.
It is a negative feedback, inverting amp. Clipping happens at 0.7 volts, so if the input waveform (from before R4) has overall voltage levels below 0.7, then clipping will not take place.
Therefore we use R6/R7 and R4 to give a gain to the Input signal so that now majority of the waveform goes above 0.7 and gets clipped by two diodes in parallel, thus giving us the distorted sound.
III. The Volume Circuit
The third Op-Amp is used for volume, to adjust the gain, So it is just a normal inverting amplifier.
The number of Op-amps used for implementation is just 4. The last two are for verifying if the circuit works.
The Background noise is input into the Circuit by the use of a mic that is found outside the Noise cancelling Headphones. This noise is inverted and played out with the normal music by the speakers of the headphones.
The first Op-Amp works as a pre-amplifer, to increase the gain of the noise, so we can operate on it.
It is just a non-inverting amplifier with some gain to amplify the signal. We can ignore the R3 due to its very high resistance. The gain is 10.
The Second opamp is an inverting amplifier with a gain of 2 to induce a phase shift of 180 degrees in the waveforms.
Third is a summing amplifier which adds the noise to the music.
The gain for noise is (1/20) to compensate for the gain we provided in the previous stages, as if we do not diminish the amplitude, proper destructive interference will not take place. The gain for music is 1.
However, we now get an inverted output due to the opamp being inverting, so we have to add another inverting buffer opamp to get the inverted noise.
This is the buffer inverting amp which plays the final output through the speakers. The output of this is the inverted noise + the normal music.
Output waveform(inverted noise+music) compared to just the music:
The summing opamp adds the normal noise, which is cancelled out by the inverted noise so we only hear the normal noise.
The Last inverting opamp is added for the same reasons (summing amp is inverting).
We can see that after simulating what happens in our ear, the output waveform is the same as input waveform
Report prepared on May 6, 2024, 11:17 p.m. by:
Report reviewed and approved by Aditya Pandia [CompSoc] on May 9, 2024, 10:49 p.m..