Conversion of mV to dB

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.
.

Jeffreybehr, as far as I know, it has to do with which test record the cartridge was measured on, JVC (3.54 cm/s) or CBS (5.0 cm/s). I don't know about the mono versus stereo numbers. I do know that you can translate between the two numbers by using basic math.

As I mentioned, the KAB calculator assumes the 5 cm/s standard, so if your cartridge is measured using the CBS standard 5 cm/s then you can just plug that value in. However, if your cartridge's output was measured using the JVC standard (3.54 cm/s) you can divide 5 by 3.54 and multply the outcome (1.4) by the output to translate the output voltage into the CBS standard of 5 cm/s.

So a cartridge that has a rated output of 0.24 mV @ 3.54 cm/s will put out the same amount of voltage as a cartridge with a rated output of 0.34 mV @ 5 cm/s.