Apologies for the nerdy comments I'm about to make, I suppose it can come across as pedantic. Meanwhile I would just like to clarify some of the 'mystery' surrounding the question why valve amplifiers are so darn cool. I would also like to add that my post count is far too high already.
Airguitar wrote:
The real difference between the sound from a tube amp vs. a solid state one has to do with the way the amp responds to transients, ie. fast changes in the wave form or signal being amplified.
Not entirely true, but often it is one of the factors. Transient response of most valve amps is faster and therefore causing less listening fatigue, since they tend to need less negative feedback than most ss amps. There are a couple of high-end sand amps with little or no feedback, the sound of which (not surprisingly) gets compared to valve amp sound. Transient intermodulation distortion (as the errors in amplifying with lots of negative feedback are called) however is something completely different from harmonic distortion occurring in valve amps when overdriven.
Airguitar wrote:
Valves tend to compress naturally when they are subject to overdriving. This also happens when they are being fed an already overdriven signal, although not as much.
Correct but note that compression only occurs when overdriven because if the input amplitude goes up, the output amplitude cannot anymore.
Airguitar wrote:
When a valve is overdriven, its inherent natural compression tends to round out the sharp, clipped edges of the waveform, making this clipping sound more musical and less brittle and harsh.
...actually it is not compression that does this, it is the nonlinearity of the valve characteristic close to maximum/minimum current levels.
Airguitar wrote:
Valves {..} have a relatively slow response to very sudden chnges in amplitude.
Eh.. No. The speed at which an amplifier stage responds to changes in the input signal is called rise time; valves stages tent to have faster rise times than sand stages. If you distinguish between amplitude (the average distance between nothing and your signal, measured over a bit of time) and the signal level itself at a certain point in time, the difference becomes clear: the valve stage is at the point of being overdriven no longer able to let the output voltage change follow the input voltage change. This is ONLY at the min/max current through the valve. It is not slow, rather it runs out of current. Because it does not pick up the linear amplification until the input signal goes below the clipping point, the amplitude is not as it should be and that we call compression. If the valve stage were just slow, it would be able to respond at no compression at a later point in time, but it will never. See?
