Hi Brent,
That's not quite correct. A 10x increase in voltage does equate to 20db, but an additional 10x increase would correspond to an overall increase of 100x, which in turn would correspond to an additional 20db, making 40db in total. 60db corresponds to a voltage gain of 1000. So the 10x increases you are referring to are multiplied in terms of voltage, but added in terms of db.
Voltage ratios convert to db based on the formula 20log(V1/V2).
In this case the 3 ohm tap of the SUT, providing 30x voltage gain, would provide a gain of 20log30 = 29.5db. The phono stage provides 37db, and the line stage 18db. So the total gain ahead of the power amp is 84.5db, or 16,788x, resulting in 16,788 x 0.24 mv = just over 4 volts, into what I presume is the balanced input of your power amp. That's probably ok, assuming your power amp's sensitivity is not highly unusual, but hopefully the power amp sensitivity is specified to require significantly less than 4 volts input to reach its full output power, or else you might find yourself having to operate the volume control closer to its maximum setting than is preferable.
Of course as we've discussed in other threads your choice of SUT gain will also be a factor in the load impedance that the cartridge sees.
The other thing to consider is the possibility of having too much gain, and consequently overloading either the phono stage or the preamp input circuits. I'm just about certain that won't be a problem even with a 30x stepup, but it's probably worth checking against the overload specs for the phono stage output and the preamp input. 37db gain applied to 7.2mv results in 0.5 volts at the phono stage output and the line stage input.
Overloading of the line stage output and the power amp input certainly will not occur, because those points are "after" the volume control.
Best regards,
-- Al
That's not quite correct. A 10x increase in voltage does equate to 20db, but an additional 10x increase would correspond to an overall increase of 100x, which in turn would correspond to an additional 20db, making 40db in total. 60db corresponds to a voltage gain of 1000. So the 10x increases you are referring to are multiplied in terms of voltage, but added in terms of db.
Voltage ratios convert to db based on the formula 20log(V1/V2).
In this case the 3 ohm tap of the SUT, providing 30x voltage gain, would provide a gain of 20log30 = 29.5db. The phono stage provides 37db, and the line stage 18db. So the total gain ahead of the power amp is 84.5db, or 16,788x, resulting in 16,788 x 0.24 mv = just over 4 volts, into what I presume is the balanced input of your power amp. That's probably ok, assuming your power amp's sensitivity is not highly unusual, but hopefully the power amp sensitivity is specified to require significantly less than 4 volts input to reach its full output power, or else you might find yourself having to operate the volume control closer to its maximum setting than is preferable.
Of course as we've discussed in other threads your choice of SUT gain will also be a factor in the load impedance that the cartridge sees.
The other thing to consider is the possibility of having too much gain, and consequently overloading either the phono stage or the preamp input circuits. I'm just about certain that won't be a problem even with a 30x stepup, but it's probably worth checking against the overload specs for the phono stage output and the preamp input. 37db gain applied to 7.2mv results in 0.5 volts at the phono stage output and the line stage input.
Overloading of the line stage output and the power amp input certainly will not occur, because those points are "after" the volume control.
Best regards,
-- Al