I know that the Zobel circuit is to maintain a certain impedance of the load of the speaker at high frequencies. When I test the circuit, the way to measure the impedance is (after measuring the output AC voltage, divide it by the output AC current), but After I came out on the side, whether there is a Zobel circuit or not, the AC current will decrease as the frequency increases. In this way, the impedance will continue to rise, so I don't understand why the Zobel circuit has no function.
Below is my circuit diagram and measure,R9 and L1 are the resistance values of the speakers measured by me.
Below is my circuit diagram and measure,R9 and L1 are the resistance values of the speakers measured by me.
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Try frequencies like 100kHz, 200kHz, 500kHz, 1MHz, 2MHz etc - this Zobel network is about stability at much higher frequencies than the audio signal itself.
Here is my test result, I found that the result is unchanged.
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A Zobel network is not useful in your circuit because it is a complementary emitter follower which generally does not need feedback compensation. However, the LM3886 is a quasi-complimentary chip which does require a Zobel network. While you may see a Zobel network applied to EF circuits, it is required for CFP aka Sziklai pair amplifiers (including quasi-complimentary) that potentially are unstable due to their local feedback. The 10 Ohm+100nF Zobel network is a pole at 160KHz, below which it has no effect. Perhaps more important than the Zobel network is a series R+L build-out that prevents the load impedance from shunting the amplifier global feedback. To understand a Zobel network, you need to understand feedback stability criteria, including phase margin and gain bandwidth product.
