D-type headphone driver based on 555 Timer can be used as an ideal utility amplifier

A widely popular 555 timer can be used as a PWM / D amplifier for instruments or other applications. It operates within a voltage range of 4.5V to 16V and can output 200 mA drive currents. The audio signal is transmitted to the CV (control voltage) pin of the 555 timer. This design example provides two simple, inexpensive drivers for headphones and audio lines, respectively, respectively, shown in Figure 1, and 2, respectively. These two drives are designed for electric guitars and violin, but they can also be applied to more other applications. For such a simple application, noise and total harmonic distortion (THD) are not a key consideration, and therefore do not measure these two values. Figure 1: Headphones and audio line drivers with operational amplifiers and NE555 timers. You can also use CMOS versions (such as LMC555), but the output current is low. Its advantages are high operating frequencies. The following is some design considerations: ● The input resistance of the CV pin is approximately 3kΩ. In most audio applications, a certain audio preamplifier / buffer is required. ● CV requires an extremely magnitude input audio signal. The desired amplitude depends on the power source of the 555 timer and the desired output audio power. ● 555 Timer is used as an oscillator, modulated by a lower frequency audio signal applied to the CV. The oscillation frequency should preferably be 10 times the maximum required audio frequency. For audio applications, the frequency should be between 60KHz and 200 kHz. This simplifies the filter out of the high frequency noise generated by the 555 timer, and maintains high switching efficiency. ● Need to pay attention to RF emissions. A first-order low pass filter should be set at least at the output of 555 timer and the speaker or headset. If the cable is long, the cable parasitic capacitance (preferably twisted pair) should be considered. The first stage gain is set to about 11 by R6 and R12 by AV1 = 1 + R6 / R12. The frequency of the timer when there is no input analog signal on CV depends on the value of R7, R8 and C5, and its standard calculation formula is as follows: F = 1.44 / ((R7 + 2R8) × C5) (Hz) The output signal of the NE555 is transmitted to the connector OUT1, OUT2, and OUT3.R9, C7, and the load can be used as a low pass filter for filtering the high frequency components generated by the timer. If not filtered, these components generate radiation, resulting in problems with sensitive electronic devices around amplifiers. The cutoff frequency of the filter should be reduced as much as possible, and a headset with a higher resistance should be selected. Be Source: Wiku Electronic Market Network

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