Tube Preamp Paired with Tube Phono Stage?

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.

Actusreus, (in case its not clear from Al's comments) the reason some preamps offer more loading settings, and that they are audible has to do with the fact that such preamps are not 'graceful', as Al put it, when dealing with RF energy. IOW, the RF energy affects the way those preamps sound.

All we ever found with loading (our preamps have a loading strip above the phono connectors so you can put anything there you want) is there is a slight change in the noise floor.

If you have a moving magnet cartridge, the loading can affect the sound of it directly, IOW the effects are occurring at audio frequencies.

Thank you, Atmasphere. This does help with understanding the issue. I don't want to keep dragging this topic, but I must ask: if Fremer (or anyone else for that matter) hears clearly definable differences in the quality of the sound, not the noise, with different resistive loads when using an MC cartridge, is he full of it?

Jtwrace,

The Andros is a beauty and everyone raves about it, but it is also nearly twice the price of the Chinook, so they are really not in the same league. If you can afford the Andros, it seems it's an easy choice, at least on paper. elast