The servo was decoupled from the current mirror, and instead acts on the input stage without being directly in the signal path. It adjusts the constant voltage sources that bias the sources of the input JFETs in order to zero the offset. Under AC conditions, the bases of the constant voltage transistors are held at a constant DC voltage by the various capacitors to ground. Therefore the servo doesn't really impact the AC behavior of the amp but it still has plenty of gain to zero the output DC offset.
amb wrote:You should never remove the DC servo from the CK²III. The amp has no global negative feedback and requires the presence of the DC servo to keep its output DC offset in check.
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