Simple Test Circuit for Tube Noise
On Sep 13, 3:36*pm, (Scott Dorsey) wrote:
wrote:
The 33 Meg resistor is being bootstrapped to at least 330 Meg. *The
bootstrap is direct coupled. *The output Z of the capsules I'm using
is ~50 Meg at 40 Hz.
How did you get that number? *What is the capacitance of the capsule when
idle?
Capsule capacitance is about 80 pF. So its output Z it just its
capacitive reactance, right?
As long as the leak resistance is low enough to permit all the spurious
charge appearing on the grid to be grounded out, you're fine. *The amount
of spurious charge that appears there is dependant on the kind of tube you
use and it's one of the more important things to select when you pick a
tube for microphone applications.
What do you mean by "spurious charge"? Do you mean input current?
Sean B
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