My 30 Watt class A is louder than my 100 Watt Class AB?

mwood:

I'm assuming your preamp has a resistive volume control. If that's the case. the "higher" the volume setting the less resistance. That's preferable for better sound. It's been the case for decades that many home audio preamps have much more gain than they need or is desirable. If your volume settings run only up to, say halfway before maxing out, your preamp has too much gain. Your tube preamp 3-5 db gain was actually better suited to your system than the 9db gain preamp. 

Excess gain preamps that result in volume settings between 1-5 have trained users to expect that. When a preamp with a resistive attenuator is used mostly between 5-9 (on a scale of 10) that's ideal, but seems wrong due to previous experience with excessive gain preamps. The output voltage of the preamp should drive the amplifier to maximum power output at just about the full volume setting. That's when the attenuator is resisting the least and converting as little as possible of the voltage gain to heat.

I’m assuming your preamp has a resistive volume control. If that’s the case. the "higher" the volume setting the less resistance.

"Less resistance" where?

You don’t know where the volume control (VC) is located. Is it the first device in the chain functionally a load for the source, or is there an input buffer then the VC, or is it on the output of the preamp which would be very unusual. In any of those scenarios, the total resistance seen by the previous stage will include whatever is loading the VC, which may be so high compared to the VC that the total resistance is effectively constant.

The output voltage of the preamp should drive the amplifier to maximum power output at just about the full volume setting. That’s when the attenuator is resisting the least and converting as little as possible of the voltage gain to heat.

This assumes the VC is at the output of the preamp. This is extremely unusual. It is also inconsequential if it is. The output impedance of the pre will be much lower than the input impedance of the amp so the load it presents will be effectively constant no matter the volume. The VC will dissipate the same amount of heat (extremely little) whatever the volume so it simply doesn’t matter.

The bottom line is without knowing  the topology of the preamp you simply have no idea how the VC is affecting anything. . In any case, it doesn’t work as you described.

I compared a 100w / Channel Shiit Vidar against a 50W / Crown amp. The Vidar had slightly more low-end punch, but the 45yr old 50W Crown amp left it behind when it came to loudness with no distortion. I am not sure why?  When I got a 30W tube amp running KT 77s it seems louder than both with greater dynamics.  I was amazed, but happy!  I think tubes have higher gain. I am sure some electrical engineer could explain.