Input sensitivity, Gain and Preamp matching

As I recall the amp's sensitivity needs to be about .5v. I tried a passive line stage with an amp having 1v sensitivity once with a poor result.

Just a guess that you need a higher gain pre as well, but others with weighty authority here can tell you.

I'd just scrap the idea of a passive pre altogether no matter what amp you consider. In the long run, I'm guessing you will not be happy.

I'm sure Al (Almarg) will see this. He is the master at these type of questions. Whatever he says, listen to his advice.

Active pre-amp would be the safe bet, even more so with a tube or SET amp, but each active pre-amp will impart a sonic signature of some sort. That's just a fact. So if teh goal is to keep that out of teh equation just don't overpay on the passive and give it a try if you must but be prepared to make tweak from there and make changes as needed. Its the usual routine. These things seldom work out just perfectly after the first crack, especially with more esoteric gear like SET amps and passive pre-amps, but things can be tweaked and refined over time. There are many ways to skin the cat which is what helps make all this stuff fun.

Thank you most kindly, Mofi. I should qualify your statement, though, by saying that at best I'm just an amateur master, while Ralph (Atmasphere) is of course a professional master :-)

Pani, Ralph frequently makes the excellent point he states above that to perform at its sonic best a SET should be operated within just a relatively small fraction of its rated power, such as 25%. Unless, and perhaps even if, your speakers are super-efficient, though, such as being in the 103 db area he mentioned, I personally would nevertheless want to have the flexibility of being able to drive the amp to full power, even if it is only a relatively few recordings having particularly wide dynamic range that might require that.

If you are using the single-ended output of a typical digital source, its maximum output won't usually be much if anything over 2 volts. And it will be less than that for many recordings. So with 0 db of preamp gain (meaning, with the volume control set at max, that preamp voltage out = preamp voltage in) you would not be able to drive the amp to full power. On the other hand I believe that some of the Slagle autoformer-based passive preamps, as in the case of the one-stage tube preamp you are considering, provide up to around 6 or 7 db of voltage gain. That would result in their output being double the voltage they are provided with when the volume control is set at max. That would probably allow you to drive the amp to full power with many and perhaps most recordings, but almost certainly not with some.

Perhaps more significantly, if I'm recalling correctly you use a high quality analog source. Most (although not all) cartridge/phono stage combinations provide significantly lower peak output levels than digital sources, for nearly all recordings (the cannon blasts on the famous and nearly unplayable early edition of the Telarc 1812 Overture perhaps being a rare exception :-)).

So it seems to me that even with 6 db of gain you would at best be introducing a significant marginality into the system, that would probably prove to be unsatisfactory for some recordings. Especially if your speakers are not in the 103 db/1 watt/1 meter area that Ralph referred to, or higher. Personally, my instinct would be to pursue a different path.

IMO. Good luck. Regards,
-- Al