This is a circuit that generates white noise, rolled-off to drive earphones or a small speaker. White noise creates is a `rushing` sound, which sounds something like air rushing by your ear(s). White noise would be flat with frequency, and since this circuit rolls off within the audio range, I refer to it as `rolled-off` noise. White (or rolled-off) noise is said to be useful in helping people improve concentration, to make a `noise wall` to improve privacy, to fill empty spaces with sound so they don't feel so empty (done a lot in larger office buildings) and has been touted as a therapy for Tinnitus (ringing in the ears).
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Q2 is a grounded emitter (inverting) amplifier with Q1 in its feedback path. Notice that Q1 is connected kind of "upside down" in that the emitter is positive with respect to its base, so that the junction avalanches, dropping about 5 to 6 volts across the junction. The purpose of Q2 is to provide just enough bias current to make the emitter-base junction of Q1 break down, and under this condition, there is a millivolt or two of broadband noise across the Q2 junction as well. Note that the collector of Q1 is not connected to anything. In the July 2003 version, the collector of Q1 was connected to the base of Q2, but I have since learned that some transistors exhibit negative impedance characteristics when connected in this manner, so the circuit has been revised to take the current signal from the base instead of the collector.
A1 is a voltage follower that buffers the 50% of the battery voltage derived by the two 470k resistors connected to its non inverting input. The 50% voltage is used as a DC bias supply for the other three amplifiers on the chip.
A2 and A3 provide a gain of 50X each, for a total gain of 2500X. The plot of open loop gain vs frequency for the LM324 shows the bandwidth intercepting the 50X gain point at about 5 kHz, so this filtering provides some "coloration" of the noise. Your choice of headphones or speakers will also color the signal. You can get back some of the bandwidth by putting a small...
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Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
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The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
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This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
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