What amp do you use with your passive pre?

OK let me try to clarify few things in my mind.
I assume every amplifier manufacturer gives the input sensitivity as per watt not at full power.
Let's say there are two amps.

Amp A:
Input sensitivity: 500mv
Input impedance: 100kOhm
Power output: 40 watts in 8 ohms

Amp B:
Input sensitivity: 100mv
Input impedance: 30kOhm
Power output: 100 watts in 8 ohms

So Amp A should be 500mv x 40 watts =20000mv/2v
Amp B should be 250mv x 100 watts = 25000mv/2.5v

Some amp manufacturers write 1.5v for input sensitivity in their specs. Does this still mean per watt? Because if so then at full power it is crazy high. Say if they mean 1.5v per watt and its output is 80 wpc. Then the input sensitivity is 120v!!!


One last question:
I have a DAC at 3v output. And my music streamer is connected to my DAC via coaxial, has 2v output. Don't know if the streamer's numbers are important here or not??

However, what I just wrote above is different than this. The specs below is from Nelson Pass First Watt J2.

Output power in 8 and 4 ohms respectively.
30 watts @ 1% THD, 1KHz
15 watts @ 1% THD, 1 KHz

Input Sensitivity 280 mV = 1 watt, 1.4 V = rated power

According to what I wrote above,
280mV x 30 watts should be 8400mV but this is 1.4V at rated power.

OK let me try to clarify few things in my mind.
I assume every amplifier manufacturer gives the input sensitivity

I’ve only ever seen the input sensitivity (in volts or millivolts) for amps as stated for the amps full wattage output just before clipping. Unless specifically stated for only 1 watt of output

Speakers sensitivity (where you maybe getting confused) is stated as sensitivity in dB for for 1watt input .

Cheers George

@georgehifi no not confused with dB. 

So, unless stated like First Watt J2, it is always stated at full power?

Yes with poweramps, input sensitivity is usually stated as the maximum voltage input, at which time the amp is just below going into hard clipping usually into an 8ohms load.

Cheers George