The zener diodes D1,D2 shown in fig5 of the ESP DoZ article are used to stabilize the bias voltage for the the input stage and also the second and output stages of the amplifier. The bias applied is adjustable to set the bias current correctly, according to the instructions.
Fig 5 is actually the finished design of DoZ (since October 2000), so this is what the specifications refer to and there aren't really any other versions now. The previous figures only show the stages of circuit development so you can better understand how it works and why the various features are necessary.
Fig 5 is actually the finished design of DoZ (since October 2000), so this is what the specifications refer to and there aren't really any other versions now. The previous figures only show the stages of circuit development so you can better understand how it works and why the various features are necessary.
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