You can use the servo to synthesize the equivalent of a 530 H inductor in parallel with a 47 kohm resistor. Together with the 120 nF coupling capacitor, that results in Q ~= (1/2) √2. The cartridge impedance will be negligible at 20 Hz, compared to the rest.
This is an example schematic. It should work with op-amps, but may need some changes to make it practical with valves:
The resistors have E96 values. Some capacitors have an E24 value (20 nF), but can easily be changed into two 10 nF capacitors in parallel. The commas are Dutch notation for a decimal point.
This is an example schematic. It should work with op-amps, but may need some changes to make it practical with valves:
The resistors have E96 values. Some capacitors have an E24 value (20 nF), but can easily be changed into two 10 nF capacitors in parallel. The commas are Dutch notation for a decimal point.
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Ah, thank you. I'd misinterpteted the series capacitor to mean in series with the forward path resistor 169R instead of the 3u3F in the reverse path. Wrong opamp!
Chris
Chris