Guys,
Here is what we know so far:
1. SS - slam, fatigue
2. Tube - musical, non-fatigue
The question is why?
3. SS - characterized by capacitance. Output stage is capacitive and semiconductors are inherently capacitive too.
4. Tube - characterized by inductance. Output stage is inductive.
Equations:
5. Capacitor - characterized by I = C dV/dt (voltage is leading current)
6. Inductor - characterized by V = L dI/dt (current is leading voltage)
where,
I = current
dV/dt = differential change in voltage with respect to time
V = voltage
dI/dt = differential change in current with respect to time
Spare me the math, why?
7. Signals that we hear are characterized by:
a. Hard sounding - rapid increase of energy specially when drums are hit, doors are slammed, hard objects falling on the floors
b. Soft sounding - gentle plucking of guitars, whisper, gentle tapping
8. For capacitors, in situation (a) the current is a very high spike with amplitude approaching infinity (very high dV/dt - you see this when you short a fully charge capacitor) depending on the change or rapid increase of voltage (or signal). The energy or power then (power = voltage x current) at this instant of time becomes very high. This is what I believe is the "slam".
9. For inductors, in situation (a) the current is a slow ramp with amplitude similar approaching that of the voltage for the duration of the signal. For a square pulse voltage the current is a sawtooth. The energy or power then at this instant of time is low due to the slow ramp. This is what I believe is "musical" or "realistic".
10. The truth however, is that hard sounding and soft sounding cannot have energy that is either too high or too low (or delayed for that matter). For signals to approach what we hear, voltage and current must be in phase with similar magnitudes. In other words, neither inductive nor capacitive.
11. The challenge then is how to design an amplifier that is approximates the characteristic of a resistor but can amplify without being capacitive nor inductive.