Input sensitivity, Gain and Preamp matching

Pani,
My experience is based ONLY on TVC and not other types of passives. But nevertheless, I would like to share.
Your amp's sensitivity is actually very low. The way people would look at the sensitivity would be - if it requires less volts for full power, then it is high sensitivity. If it requires more volts for full power, then it is low sensitivity. For a passive to work with an amp, the max sensitivity that you should go for an amp would be 1.5V for full power. The lower the better. My amp is 1V for full power,and I use a TVC. Or else, like Al mentioned, you will not hear the "full potential" of your system. Also Ralph has mentioned about speaker sensitivity - this also plays very important role in a "passive based" system. Ideally your speakers should be 90+db.
At this point, it looks like active pre would be the way for you, unless you change some components in your system.

Most SETs have low gain because they are intended to be used with high efficiency loudspeakers (usually 98 db or more).

Thanks everyone for responding on this one.

My source is mostly analog. A Naim Superline phonostage. I am sure it puts out around 3 volts because my cartridge has an output of 0.5 mv fed into full MC gain of the phonostage.

My speakers are Tannoy Turnberry SE which are only 93 db sensitive (not 103 db). Currently I use a Wavac 300B SET which produces only 9 watts. On 70% of the music I do not hear compression in my room (150 sqft). But there is still 30% of the music which I cannot listen at my desired volume levels. The amp I am considering now has parallel 300B and produces 16 watts (conservatively) per channel. I know I will better with more power but if this is going to solve the power issue with say 95% of my music I am still happy because the combination of Tannoy and 300B SET is amazing.

BTW, isnt it true that a power amp should ideally run at full gain (not full power) all the time ? That is how one can get the best dynamics at any given volume level IMO. All studio amps have a gain control which are always kept at max level. My understanding was that the input sensitivity decides the ease with which one can get the amp to full gain.

Secondly there is this concept of voltage gain amplifiers and current gain amplifiers. Does that have anything to do in this discussion ?

Pani, the Naim Superline has a specified gain of 64 db. That corresponds to a voltage multiplication of 1585. (20 x logarithm 1585 = 64). So the 0.5 mv output of your cartridge under the standard test conditions would be raised by the phono stage to 0.5 mv x 1585 = 0.79 volts. However the maximum levels of some recordings may exceed those standard test conditions several-fold, I believe by something like a factor of 5 in at least a few cases. So there may be SOME recordings on which the max level of the phono stage output might reach 3 or even 4 volts. But as far as I am aware that won't be the case with most recordings.

Also, keep in mind that the difference between 16 watts and 9 watts is just 2.5 db, which subjectively is not all that much of a difference. If you presently cannot listen to 30% of the music at desired volume levels, I would not expect that a 2.5 db increase in power would represent a solution. And even more so considering that on many recordings you may not be able to utilize much or any of that added power if you do go with a low or no gain preamp, because of the amp's low sensitivity (corresponding to a high sensitivity number, as was pointed out).

Re your question about running power amps at full gain, if the amp has a volume control and is used with a preamp having a volume control, yes, chances are that in general it would be preferable to run the power amp's control at max, which in effect takes it (and any adverse sonic effects it might contribute) out of the signal path. On the other hand, though, there may be some cases where that benefit would be outweighed by other considerations. One example perhaps being a need to increase the signal level at the output of the preamp in order to minimize the audibility of groundloop-related noise, and another example perhaps being a need to avoid running the preamp's volume control undesirably close to the bottom of its range.

I believe that your last question relates to what Ralph (Atmasphere) often refers to as power paradigm vs. voltage paradigm amplifiers, which is a separate subject relating to matching amplifiers and speakers in a manner that will result in proper tonal balance.

Good luck, however you decide to proceed. Regards,
-- Al