NE5532 0P275 Op-Amp Building Noise Canceling Headphones
Well, maybe not in a position to draw a forest quiet for an hour or two, but you can block background noise with noise-canceling headphones. The theory behind this project is that by picking up ambient sound with a microphone and reproducing it in the phase, we can actively cancel or “null” background noise. In fact, several commercially available devices perform the same function. However, building your own headphones, you can add functionality not otherwise available and have fun while you do it! With the noise performance, so that Active Noise-Cancelling Headphones to you in an auxiliary tank with line-level signal from a CD or cassette mix. This allows you to minimize the background noise while listening to music quietly. The project also has a phase inverters that allow you to keep the microphone signals in phase, thus enabling enhanced in the background. In addition, the design of hearing protection for many other interesting features, we will see later.
How it works. The electronics consists of three op-amp circuits, each built around half of a dual operational amplifiers NE5532. Each circuit uses op-amp in a different configuration. The first circuit is a non-inverting amplifier, the second is a unity-gain phase inverter, and the third is an inverting amplifier headphones. Since the hearing protection is a stereo device, the circuit actualty two identical circuits together. A channel is described, the second channel works exactly the same way.
First The hearing protection is a simple phase-inverting amplifier. All sounds played on the headphones reversed to cancel the original sounds, nothing but silence. The amount of cancellation can be adapted for different situations. Can listen to a CD or cassette, if you want to “fill the silence.”
The diagram shows the structure of the electronic part of the project. A headset is installed, J1, connected a 1/8-inch stereo jack. Electret microphones require a 2 – bias voltage of 10 volts for internal FET preamp. It is supplied with electricity from R2. A network of blood-division, which is decoupled from the bias voltage of the power supply provided by R and Cl This is necessary because of the high amplification of the signal chain.
The signals from the microphone, then ICL one go. set a NE5532 preamp than a standard non-inverting. The gain is set to a higher R8/R6 ratio in the feedback path. The total gain for this stage is about 31 dB. The resistor R4 provides a ground reference for the precursor. A pair of high-pass filter and is formed by C2/R4 C4/R6. These filters block DC, trying to slip through the preamplifier.
The output of the preamplifier, the microphone signal sent to two different ways. It feeds on both a center of SL-A and phase-inverter. The phase inverter is nothing more than a second NE5532 configured as a unity gain op-amp switch (IC2-A). The output of IC2-A is connected to the other pole of the SL-A. In this way, SL-A, either the opposite or non-inverted signal. The signal selected by the common Pole SL-A is the potentiometer R14-a. This control adjusts the signal level feeding the mic headphone amplifier.
The headphone amplifier is built around IC3-A, third NE5532 operational amplifier connected as an inverting stage. The gain is here defined as the ratio of R19/R15. This type of op-amp configuration can be easily modified to add the functionality through a summary of the involvement of R17. The second input comes from an additional line input is attenuated by potentiometer R23-a.
There’s a reason why it was selected 10K ohms to the value of R15 and R17. In addition to maintaining manageable levels of R19 10K ohm resistors interact with 100k ohm linear potentiometer. Potentiometers then behave logarithmically.
This is how the device works: One end of the potentiometer is connected to the earth, because we use it as a voltage divider. Since the intersection sum-ming is an op-amp is a virtual place, the 10K ohm resistor is essentially tied to the land. This affects the response of the potentiometer, the potentiometer is turned on, there is a larger increase in production as the end of the potentiometer travel is reached. This leads to a steady increase in the volume of the received signal. Potentiometer with a cone-audio course available, but a linear taper device is getting easier and costs less.
The output amplifier is coupled to the headphone output J3 by R21. This provides resistance to protect against overload IC3-A when the output is shorted. If you have never used one operational amplifier for driving headphones, you are beautiful in a surprise. The NE5532 will provide a signal of 10 volts RMS into a load of 600 ohms with very low distortion. This corresponds to 166 mW of power. Most personal stereos deliver only 20 to 30 mW for a helmet.
A final note on the use of operational amplifiers as headphone amplifier: Most generics not enough power to function properly can. Some replacement for the NE5532 are known to the work of the 0P275 from Analog Devices, Burr Brown OPA2604 on, and the LM833 from National Semiconductor to be heard. These components are made from several sources, including from Digi-Key, Allied Electronics and Jameco available.
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