Conversion of mV to dB

Thank you both. I agree the KAB calculator needs to be used with caution as it does not take into consideration all of the parameters that might come into play when trying to convert different values. It appears that an accurate calculation can be done using the formula of 20 log (V1/V2) where V1 is the preamp's nominal output in terms of V rms and V2 is the sensitivity setting that is being converted. The preamp's nominal output is listed as 2V rms so let's say for the 1.4 mV setting, the gain would be 63 dB. This perfectly reflects the range provided by the manufacturer of 52-76 db from the lowest to the highest setting.

I owe credit for this to, and would like to thank, Al (Almarg), whose advice has been absolutely invaluable to me since becoming an Audiogon member. Thanks Al!

Thanks Al. Let me just add that the designer himself stated to me that the setting of 1.4 mV corresponds to approximately 70 dB of gain, and 0.6 mV to approximately 68 dB, which essentially matches to the values obtained by using the formula.

Also, the assertion that "[a] phono preamp cannot output more than a few 100s of mV as it will overload the linestage pre" surely cannot be true. The Parasound JC-3 has a nominal output of 1V, and it will probably output way more than that in peaks. The Sensor is listed to have the max output of a whopping 8V, which I don't quite understand, but certainly the designer would not design it this way if it was likely to be incompatible with most of the line preamps on the market. I certainly didn't experience any incompatibility with my line preamp, which btw outputs 1.5V whereas my power amps are listed as having input sensitivity of 1V, and they are all from the same manufacturer. Needles to say, they work very well together. Sounds like the issue is more complicated than just pure numbers on paper. I also apologize for not providing more information to begin with, which is never a good way to ask for advice. However, I simply and honestly did not know what information was pertinent to the answer.

As a follow up, I looked up specifications for some phono and line preamps out of curiosity. My Rogue preamp has "rated" output of 1.5V, but "maximum" output of 30V PP ("peak power"?)!!! With the power amps listed as having input sensitivity of 1V RMS, it sounds like a bad match, on paper, but definitely not in reality.

Also, the Rogue Ares phono preamp, is listed as having rated output of 1V and maximum output of 8V RMS @ 1KHz. Based on this, and in light of our conversation, I would venture an uneducated guess that the max values are not truly relevant in real life conditions, and even the nominal value in case of the phono pre would depend on either the cartridge's output or the gain setting. So Bombaywalla's assertion might as well be true in that under real life conditions a phono pre will not output 2 or more V's. Otherwise, these figures wouldn't make much sense...

Ahh, the attenuator on the line preamp! Sometimes the obvious avoids us (at least me :).

Yes, the first figure is a mistake; it was supposed to state "0.4 mV" not "1.4 mV." Hazards of posting late. These figures are a few dB off from what is obtained using the formula, but he did say "approximately." Thank you for pointing it out, Al.