Bias adjustment without oscilloscope Vs bias adjustment with oscilloscope, hybrid expandable booster
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Correction: in the oscilloscope adjustment it was with a sinusoidal signal of 2.4 khz. facebook group: / 530292354453846 A poor Bias polarization will cause zero crossing distortion, an over bias polarization will cause excessive heating of the amplifier reducing its efficiency and durability, it could even severely damage the equipment. In the Bias adjustment part with the multimeter for those who are just starting: It is advisable to use alligator clips to facilitate the adjustment, it is advisable to remain between 400 and 500mV from base to emitter of output transistors respectively, this adjustment is without input signal, without load connected to the amplifier output and using the series lamp in the amplifier power supply (I recommend 100w series lamp). Bias adjustment with the multimeter for experts: This adjustment is based on the current (in mA) that flows through the output transistors, this current can be calculated by applying Ohm's law (I = V / R), the voltage across the emitter resistors of the output transistors is measured, the value of this resistor is known and fixed (typical values are 0.22Ω, 0.33Ω, 0.47Ω), and by measuring the voltage, the current that flows through the output transistor can be calculated. How many mA should flow through the output transistors? This criterion varies depending on the designer / manufacturer of the equipment and can range from approximately 5mA to 10mA. This method has the disadvantage that it requires high precision/resolution measuring instruments, so I do not recommend it for beginners, since a beginner will not always have access to a multimeter with the appropriate features. That is why I recommend that those who are just starting out measure between the base and emitter of output transistors, since an average multimeter would have a more acceptable precision in the range of 0.5V than in the range of a few millivolts. Ultimately, the most optimal and professional adjustment is using a signal generator, oscilloscope, and phantom load. In the bias adjustment part with the oscilloscope, the optimal adjustment point is when the zero crossing distortion disappears, at that moment is when you should stop moving the potentiometer. For this adjustment, you should initially leave the bias polarization as low as possible, since when using input signal and load at the amplifier output, the series lamp is not used for this adjustment. The card used in this video is based on the expandable hybrid card popularized by Mr. Joaquin from the Ampletos page Build your own videorokola. Complementary videos on the topic of BIAS Part 1. • A pre-introduction of what is pol... Part 2. • A pre-introduction of what is pol...
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