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RE: Poor Design for a Preamp

Regarding the voltage divider . . . couldn't he just use a 33 ohm in series and a 10 ohm to ground? The voltage reduction would be the same.

The resulting output impedance would then be dominated by the impedance of the tube which, assuming a 50k load resistor, would be 8.33k.

If the formula I posted is correct (??) the output impedance would be:

(8.33k + 33 ohms) + (10 ohms || the assumed 100k input impedance of the amp) = 8363 ohms + 9.99 ohms = 8373 / 8.373k

Looks like this would move the rolloff point to ~108k if only the 175pf capacitance of the cable is included.

Am I missing something?


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