I came across a passive pre-amp that has 15k ohm input impedance and a MAXIMUM output impedance of 3750 ohms. I cannot see how that is possible prom a passive pre amp. If it's just a basically a pot, then when the volume is turned down very low, output impedance is going to be roughly equal to the value of the pot in series with the output impedance of the source.
If that is possible then perhaps passive pre-amps are not so bad after all. But does anyone know how it's done? I feel like I am missing something.
If that is possible then perhaps passive pre-amps are not so bad after all. But does anyone know how it's done? I feel like I am missing something.
mr.duck said:
Not only is this possible, it is a certainty. The maximum output impedance of a potentiometer occurs when it is mid-travel (electrically not mechanically if it is a log pot). If the source has an output impedance close to zero then effectively you have the two halves of the track in parallel. As each half has a resistance of 7k5, the resulting output impedance will be 3k75. The output impedance will fall towards zero as the potentiometer is rotated towards its maximum or minimum positions.
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