Preamp gain vs. poweramp sensitivity

@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!

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. 

That is simply incorrect. More gain from that component may have improved the sound in your system, or perhaps you are confusing louder with better, but there is absolutely no consistent correlation betweeen increased gain and better sound.