Tubes vs. solid state.

Unamplified comes to mind first whenever live is mentioned.

And the reason tube amps are loved by guitar players is that they overdrive them into distortion frequently. We all know about tubes even order harmonics when overdriven. How many of you overdrive your home stereo to get that classic distorted rock & roll sound that people like Clapton seem to enjoy so much?
I'm not arguing against tubes, but it's my position that they have a much more practical application in the world of guitar amplifiers than in home audio.

Olesonmd has the critical point - the whole point of tubes in guitar amps is their overload characteristics - in audio, while the way tubes overload may *help* certain things, we want them out of that range!

Yes, Ralph, I would like to hear everything that chaos theory has to say about tubes and audio amplification.

I type this as I listen to an ASR Emitter, which is certainly among the very best, I mean the absolute best, amps I have ever heard, and no tube anywhere.

Alright- here are some basics:

Given an amplifier with a propagation delay (IOW, any amplifier), and a constantly changing waveform (such as a musical signal), the application of loop feedback (negative feedback) creates a 'non-linear dynamic system' which will have chaotic response including signal bifurcation (we audiophiles call bifurcation 'distortion').

In this case, the bifurcation will generate a large amount of harmonics- up to and past the 85th harmonic. There will also be inharmonic distortion- bifurcation that is not exact doubling or tripling due to interaction with intermodulations occurring at the feedback node(s).

The resulting harmonics will be low amplitude and we see this all the time in amplifier specs. The chaotic response cannot be avoided if feedback is applied, and forms an artificial noise floor quite unlike the normal noise floor seen in real life and also in audio circuits that do not employ feedback. The fact that the spectra of noise in a room or a zero feedback audio circuit is nearly identical should not be a surprise as the chaotic behavior of random elements (tubes, transistors, resistors) follow the same rules as is found in a room.

Our ears have the ability to hear about 20 db into natural noise floors, giving us the ability to extract spatial information even if the wind is blowing. The artificial noise floor generated by feedback (chaotic response) cannot be penetrated by our ears in the same manner so any spatial information below that threshold is lost.

This is why amplifier circuits that employ feedback seem to contain less soundstage information. It is also why they seem to sound brighter.

So Chaos Theory is telling us that loop negative feedback cannot be effectively used to eliminate distortion! Other means must be used. To create linearity, we must use the most linear forms of amplification known, otherwise signal bifurcation will be the result.

Now many of you might well be saying 'isn't negative feedack a stabilizing factor in amplifier design?'. While in audio this has been accepted as fact, Chaos Theory teaches something a little different: that the non-linear dynamic system has a stable operating zone (this is the one where we apply a sine wave to the input). In order for the system to have a true stable condition, the feedback has to be **positive** and so will result in the amplifier going into oscillation- when the amplifier oscillates, its condition is now stable; it will not change until the system is shut down. Of course we have no use for that in audio amplification :)

This is the tip of the iceberg, but in this lesson we have seen that Chaos Theory predicts what Norm Crowhurst wrote about in the 1950s- that feedback injects noise into the amplifier. The energy of the distortion is not substantially reduced by feedback- it is chopped up (bifurcated) and spread out over a wide spectrum with a lot of the energy in the ultrasonic range.

Fascinating stuff huh??