Regarding the adequacy of 76 db of SUT + phono stage gain, that is 7 db more than the OP presently has. For a typical rotary volume control, which when viewed as a clock dial can be adjusted between limits of say 6:30 or 7 o’clock at min and 5 or 5:30 o’clock at max, and is used in the upper half of its range, a 7 db difference probably corresponds to a bit more than 45 degrees of rotation. For example, see the dial calibrations shown in this photo, although the photo is of an MFA passive (not active) preamp.
So **if** the volume control on the OP’s Herron preamp has similar rotational limits (approximately 6:30 or 7 o’clock and 5 or 5:30 o’clock or so) he should be able to approximately judge the effects on noise level of 7 db of additional gain by reducing the volume control setting by a bit more than 45 degrees, and seeing how that change in setting affects noise levels when no music is playing.
Also, I agree with Folkfreak that it in general it would be wise to assure that the combination of cartridge output rating, SUT gain, phono stage gain, and line stage gain is adequate to drive the power amp to full power. Even if the most power that is ever used is say half of the amp’s capability, that would only be 3 db less than full power. So if full power can’t be obtained even with the volume control at max (which is the position at which the preamp will provide its rated gain), 3 db less than full power may not be attainable at any volume control setting either. And regarding the KAB calculator, it can be important to note that the calculations of phono stage gain which it provides are based on boosting the cartridge’s rated output to only 325 mv.
Regards,
-- Al
So **if** the volume control on the OP’s Herron preamp has similar rotational limits (approximately 6:30 or 7 o’clock and 5 or 5:30 o’clock or so) he should be able to approximately judge the effects on noise level of 7 db of additional gain by reducing the volume control setting by a bit more than 45 degrees, and seeing how that change in setting affects noise levels when no music is playing.
Also, I agree with Folkfreak that it in general it would be wise to assure that the combination of cartridge output rating, SUT gain, phono stage gain, and line stage gain is adequate to drive the power amp to full power. Even if the most power that is ever used is say half of the amp’s capability, that would only be 3 db less than full power. So if full power can’t be obtained even with the volume control at max (which is the position at which the preamp will provide its rated gain), 3 db less than full power may not be attainable at any volume control setting either. And regarding the KAB calculator, it can be important to note that the calculations of phono stage gain which it provides are based on boosting the cartridge’s rated output to only 325 mv.
Regards,
-- Al