Changing the internal 47K resistor in the preamp to 120K will not affect the gain significantly, but has the two potential disadvantages that I mentioned (internal preamp modification; possible subtle electrical effects).
Putting an external 73K or so resistor in series avoids those disadvantages, but will reduce the signal level into the preamp by 8.1 db, corresponding to 20 x log (47/120). That would cause you to turn up the volume control by 8.1 db to get the volume you would have gotten without the series resistor, which in turn would raise the background hiss level by 8.1 db.
That may or may not be significant, depending on the signal-to-noise ratio of the preamp, which you can roughly judge by seeing what the hiss levels are that you presently have, and what they become if you turn up the volume moderately. Keep in mind the rough rule of thumb that a 10 db increase in volume corresponds to a doubling of subjectively perceived loudness.
For a "beginner," you ask remarkably intelligent questions!
Regards,
-- Al
Putting an external 73K or so resistor in series avoids those disadvantages, but will reduce the signal level into the preamp by 8.1 db, corresponding to 20 x log (47/120). That would cause you to turn up the volume control by 8.1 db to get the volume you would have gotten without the series resistor, which in turn would raise the background hiss level by 8.1 db.
That may or may not be significant, depending on the signal-to-noise ratio of the preamp, which you can roughly judge by seeing what the hiss levels are that you presently have, and what they become if you turn up the volume moderately. Keep in mind the rough rule of thumb that a 10 db increase in volume corresponds to a doubling of subjectively perceived loudness.
For a "beginner," you ask remarkably intelligent questions!
Regards,
-- Al