Conversion of mV to dB

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...

Thanks for the followups, Marek. A point to keep in mind is that the specs for maximum output, for both phono stages and line stages, refer to the maximum output that the component is capable of (without clipping or a severe rise in distortion). And in the case of a line stage, it is based on the volume control being turned all the way up, as is the specified gain of a line stage.

So that number should be much greater than the maximum output level that would ever actually be used, and it should also be much greater than the input sensitivity of the next component in the chain.

Also, "rated output" tends to not be a particularly useful figure, at least without being put into the context of the input level it is based on. The output level will be the input level factored up by the gain (expressed as a voltage ratio), and (in the case of a line stage) factored down by whatever amount of attenuation is provided by the volume control at the setting that is being used.

Finally, I believe that the reference to 70 db in the first paragraph of your post immediately following mine is a typo, and perhaps should be 60 db.

Glad the new phono stage is working out well. Best,
-- Al

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.

Almarg, Actusreus,
OK, thanx for the clarification.
wow, I have not come across a phono stage outputing a 2Vrms signal! But yeah, the link Almarg sent surely says that...
Looks like this RCM Sensor Prelude phono preamp should be set to the 1.4mV setting so that it provides 63dB of gain for MC & should be set to 5mV so that it provides 52dB gain for MM. This seems to jive with Al's statement "...the mv marking of the gain setting that is used should be significantly higher than the rated cartridge output."
So, really only 2 settings of all those provided really make sense & are really useful. One could play around w/ the other gain settings but one would get the preamp volume control out of the 12 o'clock - 2 o'clock sweet-spot zone.

Jmcgrogan2, it's been many years since I played with LPs, fonocartridges, and fonostages, but I do recall something about 5cm/s (centimeters per second) and 3.54cm/s...being that they're the same!

5cm/s is the standard horizontal groove modulation for a mono signal, and 3.54cm/s is THE SAME goove modulation measured perpendicular to the groove wall and then expressed as a stereo signal, PER CHANNEL.

...I think.
.