Tube Preamp Paired with Tube Phono Stage?

Jmcgrogan2,
I'm not sure, but as I mentioned in one of my posts above, my preamp has five gain settings so it certainly does have gain. I might be wrong, but I believe the KAB calculator only considers the gain of the phono stage. It's possible that an assumption is made as to the base line preamp gain. You can read more about this at www.kabusa.com

Btw, for a cart with an output of 0.24 mV, you apparently need 63 dB of gain so it makes sense that you found 66 dB to be more than enough. I just experienced the opposite a few times, so I am always very careful about matching the phono preamp gain with the cartridge output.

The KAB calculator considers preamp gain period. That's phono preamp + preamp gain. So the calculator said I needed 63 db and I had 66 + 22 = 88db of gain. Way more than enough. I probably could have gotten by with a phono stage with a 50-54 db of gain for my 0.24 mV output cartridge. Maybe I could have turned the volume knob up to 1 or 2 o'clock instead of 9 or 10 o'clock.

Jmcgrogan2,
That has certainly not been my experience. My current phono preamp came with a factory preset gain of 29 dB for MM cartridges and it was not enough to drive my temporary Shure M97-xE that outputs 4 mV. It simply didn't have enough volume even though I could not go past 12 o'clock when I played CDs. I then had the manufacturer up the gain to 39 dB and it solved the problem. As an experiment, I also ran the cartridge using the built-in phono stage in my then-amp, Rogue Cronus Magnum, that had a gain of 35 dB in the phono stage before the line preamplification and the difference was tremendous. According to the KAB calculator, an optimal gain for the Shure was 38 dB...

I experienced a similar problem with my original cartridge, Soundsmith Aida, which had an output of 2.12 mV, when I used it with the built-in phono stage in the Cronus. When I switched to a separate phono preamp (Soundsmith MMP3) with 43 dB of gain, the volume was much higher and just sufficient, which obviously points to the low gain in the phono stage as the problem. Well, the KAB calc is 44 dB for an output of 2.1 mV so, in my opinion and experience, it provides a pretty good estimate of an optimal gain for a given cartridge in the phono stage independent of the line stage. How differences in line stages would affect that calculation, I frankly do not know.

I took a look at the KAB Gain Calculator.

First, it clearly states in its introduction that:

The optimum gain is based on achieving 325mV rms output at 5 cm/s. For the current crop of CD recorders, 300mV is required for 0dB recording level with the recorder's level control set at max. Aiming for 325mV gives a little margin.

325 mv is not close to being enough to drive most power amps to full power, so clearly the answer provided by the calculator applies just to the phono stage, and not to the combination of phono stage and line stage.

All the gain calculator is doing is dividing the cartridge's rated output in mv into 325 mv, and converting that ratio into db based on the standard conversion formula 20log(V1/V2), where V1 and V2 are two voltages, and "log" means the base-10 logarithm.

That is very simplistic at best. Not only does it not take into account line stage gain, but it also does not take into account power amp gain, speaker sensitivity or efficiency, listening distance, and speaker type (volume falls off more rapidly with increasing distance for box-type speakers than for planar speakers, for example). All of those factors will influence the position at which the volume control will be set.

And perhaps most significantly, it does not take into account the signal-to-noise ratio of the phono stage, as I discussed earlier. One phono stage providing a given amount of gain may result in an acceptable level of background hiss, while another phono stage providing the same amount of gain may not, even though both phono stages will cause the volume control to be used at the same setting. That is especially a concern if the cartridge has a particularly low output.

In other words, the calculator should be considered as providing at best a rough rule of thumb guideline. Nothing more.

Best regards,
-- Al

I'm between the Chinook and Zesto Andros.