Page 3 of the
Rogue 99 manual provides a good answer to the op's question:
The optional all-tube phono section consists of two input tubes (12AX7), a passive RIAA equalization section, and an output section that can be configured in one of three gain levels to accommodate different cartridge output levels. Using 12AU7 tubes in the output amplification stage (the two tubes nearest the front of the unit) provides an overall gain of approximately 63dB. This is very satisfactory for moving magnet and moving coil cartridges with an output over 1mV. In this configuration the two small switches on the phono board should be in the l setting. An additional 10dB of gain can be realized by replacing the 12AU7 tubes with 12AT7 tubes. In this case the switches should be moved to the h position. This configuration is recommended for cartridge outputs of 0.4mV and up. 12AX7 tubes can also be used for even greater gain. It should be noted however that very low noise tubes must be used in the first gain stage (the two rear 12AX7 tubes) so that tube noise or rush is kept to a minimum.
The cartridge loading is factory set for 47K ohms and 150pF of capacitance. This is suitable for most moving magnet and moving coil cartridges. Special cartridge loading can be ordered from the factory or from your local dealer.
The bottom line is that with proper tube selection low output moving coils with outputs of around 0.5mv will provide enough volume, assuming the power amp does not have lower gain than typical (0.5mv followed by a gain of 75 db and no attenuation from the volume control, i.e., volume control at max, results in approximately 3 volts into the power amp).
However, both their wording and the fact that 75db overall phono stage + line stage gain is lower than typical for lomc's suggest that hiss levels may be marginal (or worse) with low output cartridges, depending on the particular tubes which are used.
Also, as everyone probably realizes, their statement about 47K loading being suitable for most moving coil cartridges is certainly not correct. It will work, but it will result in an ultrasonic resonant peak which with many mc's will have audible adverse consequences in the treble.
My point about signal-to-noise ratio was simply that, to use the figures that were used as examples earlier, a 60db phono stage followed by a 0db line stage is likely to have lower hiss levels than a 40db phono stage followed by a 20db line stage. The reason being that the higher gain phono stage figures to have been designed with lomc's in mind, while the 40db phono stage was probably intended for mm's or homc's.
Neil (Nsgarch) -- Thanks for the interesting read about the Vendetta Research unit and John Curl. Interestingly, all three of us who have responded use Mark Levinson phono stages. I'm using the phono section of an ML1 preamplifier, accessed via the tape out jacks and going into a Classe CP60 line stage preamp. I used to use the ML1 as a complete preamp, but one of its potted output amplifier modules developed a hiss problem after 30 years or so, and replacements are just about impossible to find. The ML1 phono stage design was carried forward from the phono stage of the Levinson JC-2, designed by John Curl as one of Mark Levinson's earliest products.
Regards,
-- Al
