Preamps... understanding volume...

Thanks to everyone for all the info... far more than I expected!

the relationship of strong or stronger signal going from preamp into an amp, and whether the amp can therefore produce more power for low sensitivity speakers (or any) has not been answered.

I do not know for sure, but

Isuspect the amp cannot produce more than it's maximum GUARRANTEED wpc (they often produce more power in spec than their official rating).

McIntosh preamps I have owned output 2.5v (all?). McIntosh ampsI have owned have two optional inputs (all?): alternate .75v and 2.5v to match their preamp's 2.5v. The amp only has one set of published output rating for each ohm tap (4, 8, or older equipment 16 ohms). 

They do not have lower or higher ratings depending on which input level is used. 

I always advise, whenever you buy, or switch equipment, try to find more efficient speakers you love. High power amps do not/will not damage speakers, low wattage amps can damage speakers. Efficient speakers set you up to only need/try lower power amps, especially tube amps.

Amp GUARRANTEED WPC. I owned an mc2250, rated for 250 wpc. Testing at lab day at Harveys proved it produced 320 wpc within spec. The McIntosh technician said "sir, you have an unusual unit". Printed out spec sheet showing the results, changed the McIntosh decal on the back, signed and dated it.

You never know, certainly cannot plan on it. McIntosh and NAD amps both have protection circuits to protect your speakers and themselves. They get engaged when asked (by the speakers) for more than their rating. Others probably do too, I just have no experience with others. Indicates you need more power, or more efficient speakers.

Amps are limited, in absolute terms, by

• The voltage rails in the power supplies. These provide the maximum + and - V swing.
  
• The current available from their own power supplies, before those rails sag
  
• Thermally limited in the amount of power they can output before they shut off or melt.This is why peak power may be much  greater than continuous, as well as limit the ability to deliver into low impedance loads.
  

Amps are also a fixed voltage gain. Often around 28 dB. So:
Output = ( Input + 28 dB ) OR ( MAX)
whichever is less.

erik,

does that mean a stronger input signal, from a preamp with more gain (less attenuation), boosted by amps +28db will result in higher volume output, especially important for lower sensitivity speakers like OP is asking about?

Elliott, to answer your question just above:

The gain of the preamp cannot change the amp’s maximum power capability, of course. If the maximum output voltage of the source when boosted by the gain of the preamp is enough voltage to drive the amp to its maximum power capability, additional gain will just result in the amp providing that amount of power, or a given lesser amount of power, at a lower setting of the volume control than would be the case if the preamp’s gain were lower.

The maximum output power capability of the amp, into an 8 ohm or 4 ohm resistive load, corresponds to its rated continuous power capability into those impedances, plus whatever margin may be built into those ratings, plus whatever amount of dynamic headroom the amp can provide for limited amounts of time, plus or minus whatever presumably small differences may exist between different examples of the same make and model.

Regards,
-- Al