Design Electronic Filter Circuits
Some higher-end amplifiers have very high filtering requirements for the power supply of the front and receiver, and no hum can be heard from the speakers. Here is an electronic filter with simple circuit and excellent effect, which can achieve the purpose of almost completely eliminating hum by using a small capacitor.
The principle is shown in the figure. BG1 and BG2 form a composite tube. The difference between this circuit and other circuits is that the filter element is added to the base of the composite tube. Since the amplification factor of the composite tube is β=β1·β2, the filtering effect obtained from the emitter of BG2 is β1 times that of L1 and C6. It is equivalent to adding a large capacitor and a large inductance to the circuit, and most of the hum in the circuit is suppressed. Due to the addition of L2 and C7, their filtering effect is enlarged by β2 times by BG2, further filtering out the residual hum. Another advantage of adding inductance to the base of the composite tube is that the base current is small and can be wound with very thin copper wires. The L1 and L2 of this circuit are 200 turns randomly wound on the 1/4W100K resistor with about 0.15mm copper wire.
The composite tube has a small-scale voltage stabilizing effect in this circuit. In actual production, you can choose triodes and other components according to your own requirements.
