Undertow,
If it is a simple inverting op amp configuration, with a single-ended input and a single-ended output, then yes changing a 10K feedback resistor to 5K would cut the gain of the stage in half. However, there are several complicating factors that I think may be present.
And before I get into those, consider that cutting the gain in half will only result in raising the preamp's volume control setting by 6db from the positions it is now used at, which while significant is not a huge difference.
Here is the datasheet for the CS4398:
http://www.cirrus.com/en/pubs/proDatasheet/CS4398_F1.pdf
Note on page 20 the circuit configuration they recommend be applied at the output. It performs differential-to-single ended conversion, as well as 2-pole filtering. If the configuration you are dealing with is similar (and it probably is, since the dac chip itself outputs differentially, and presumably requires similar filtering), simply changing the feedback resistor value will not result in a proportional re-scaling of the output. And more significantly, it will upset the filter parameters, with the likely result of significant sonic side-effects.
Within the audio passband, where the filtering presumably does not do anything, I believe that the relation of output voltage to the two input voltages of the stage shown on page 20 would be:
Vout = -(Out-)*(1.27/1.58) + (Out+)*(.487/1.58)*((1.27+1.58)/(.487+.604)).
Keep in mind also that as the closed loop gain is reduced, the bandwidth is increased, with possible adverse effects on ultrasonic spurii or even stability.
Sorry to muddy the waters!
Regards,
-- Al
If it is a simple inverting op amp configuration, with a single-ended input and a single-ended output, then yes changing a 10K feedback resistor to 5K would cut the gain of the stage in half. However, there are several complicating factors that I think may be present.
And before I get into those, consider that cutting the gain in half will only result in raising the preamp's volume control setting by 6db from the positions it is now used at, which while significant is not a huge difference.
Here is the datasheet for the CS4398:
http://www.cirrus.com/en/pubs/proDatasheet/CS4398_F1.pdf
Note on page 20 the circuit configuration they recommend be applied at the output. It performs differential-to-single ended conversion, as well as 2-pole filtering. If the configuration you are dealing with is similar (and it probably is, since the dac chip itself outputs differentially, and presumably requires similar filtering), simply changing the feedback resistor value will not result in a proportional re-scaling of the output. And more significantly, it will upset the filter parameters, with the likely result of significant sonic side-effects.
Within the audio passband, where the filtering presumably does not do anything, I believe that the relation of output voltage to the two input voltages of the stage shown on page 20 would be:
Vout = -(Out-)*(1.27/1.58) + (Out+)*(.487/1.58)*((1.27+1.58)/(.487+.604)).
Keep in mind also that as the closed loop gain is reduced, the bandwidth is increased, with possible adverse effects on ultrasonic spurii or even stability.
Sorry to muddy the waters!
Regards,
-- Al