Preamp gain vs. poweramp sensitivity

What I can say about gain is the improvement it can make to your system. I have an ML amp and 326S preamp, and I can set the preamp to o gain, 6db, 12db, and 18db. Each step up from zero improves the sound, I like the 12db, but I recently tried the 18Db, and what I have experienced is a more relaxed sound, more open, more dynamics in the bottom end, and just a more pleasant and natural sound without any downsides. 12Bd sounds more sharper and detailed but not as natural as the 18db, So gain does make a sonic impact which is why buying a new preamp with more gain than you had before will sound different for sure and most likely better. My vocals are now in the room with body and openness. I guess much less like a recording. 

@paulfolbrecht Yes, you were thinking about this right. Excellent numeric breakdowns by @herman!

Sensitivity in power amps is a voltage input number that has to be referenced against a specific output power level (225 Watts in your case) to resolve its voltage gain - usually it’s referenced against "full rated continuous power" (for a sinusoidal wave), regardless of what the amp actually measures at - the 300 Watts bench results are irrelevant to its sensitivity rating.

Sensitivity in speakers is a dB output number that’s usually referenced against an input of 2.83 Volts (one Watt into an 8 ohm load, or 2 Watts into 4 ohms).

Voltage multipliers have a constant factor of 20 when you calculate out their dB differential (dB = 20 * log(V1 / V2)), whereas power multipliers only have a factor of 10 (dB = 10 * log (P1 / P2)) - why is that? Because when you keep the resistive load constant (as in the downstream audio component), increasing the voltage also causes a proportional increase in current - and these increases both multiply together to create power. That’s why bridging a "high current" stereo amp (bridging always doubles its output voltage) can elicit a QUADRUPLING in power - as long as it can supply the extra current, exactly proportional to the doubled voltage :)

You amp is indeed unusually high in both gain and sensitivity. You would be wise to avoid preamps with high gain (anything above 14dB). However, I don’t think you necessarily need to stick to passives. When you combine high gain preamp w/ high sensitivity amp & high sensitivity speakers, you will likely face a high noise floor (white noise, hissss). I like Tannoys with lots of tube power, so I’ve been there before.

Tube amps tend to have a higher sensitivity (lower voltage required to hit full output) than solid state amps, though of course there are exceptions. I had an 1950s/60s Eico HF-87 tube amp that was rated at 35 Watts/ch and had a sensitivity of 0.38V. It had a deceivingly high gain (33dB). This is incidentally the same gain as my Rogue Apollo tube monoblocks, which are rated at 1 Volt for full 250 Watts output power. These amps have a noticeably higher gain than any other amps I’ve used! When you see a 12AX7 in V1, get ready for a lot of gain :) 

My passive LDR Tortuga Audio preamp is not lacking in any area. Try one and see for yourself.

@mulveling 

awesome explanation!