Conversion of mV to dB

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.

John and Jeff, I believe that BOTH of your statements are correct, but there are several factors that muddle the issue.

5 cm/s lateral velocity corresponds to 3.54 cm/s at 45 degrees, meaning 3.54 cm/s in each channel, as Jeff indicated. Also, however, 5 cm/s peak in a given direction corresponds to 3.54 cm/s RMS in that same direction.

See the photos of the labels of CBS and JVC test records near the end of this thread, and also see some of the preceding posts. The 1 kHz test tones on the CBS record are clearly indicated on the label as being at 3.54 cm/s RMS at 45 degrees, which corresponds to 5 cm/s peak at 45 degrees. The JVC record is also marked as 3.54 cm/s at 45 degrees, but with no indication as to whether that is RMS or peak. Measurements cited in the thread indicate that figure is peak, implying only 2.5 cm/s RMS, which is 3 db less than on the CBS record.

So comparing apples to apples, and using peak figures at 45 degrees, John is correct that CBS is 5 cm/s and JVC is 3.54 cm/s. Which leaves open the question, however, of what a cartridge specification is referring to if it refers to "3.54 cm/s." I have no particular knowledge of that, but it wouldn't surprise me if some manufacturers are referring to 3.54 cm/s RMS per the CBS record, corresponding to 5 cm/s peak, while others are referring to 3.54 cm/s as marked on the JVC record, which is peak and therefore only 2.5 cm/s RMS.

Fortunately, though, the difference is only 3 db.

Best regards,
-- Al