I am amazed how almost any sound can be synthesized with modern electronics. I can play a number of instruments and what gets me most is that a sound card can put out a quality that is just as good. This implies that the sound is nothing more than a summation and a device capable of outputting any waveform could reproduce that sound exactly. So my question is can they build a sound card that sounds exactly like these revered tube amps?

For a simple version:
1. Measure the frequency response, and determine the Bode plot.
2. measure the transfer function (V out vs. V in), and store in a look-up table

Then sample the waveform, and apply IIR filters to match the Bode plot.
Form the output of the filter, look up the output voltage in the look-up table, then output to the DAC.

 

No reason why it shouldn't. See the chapter in Doug Self's book about class A. His is just a standard class B amplifier with the bias increased.

Then a guess the definition of Genuine Class A operation has different meaning to different people. I'd call a class B with the bias increased a Class AB. Someone even wrote that in this nice summary...
https://en.m.wikipedia.org/wiki/Power_amplifier_classes#Class_AB

 

I think a push pull circuit could be called class A if neither transistor is ever in cutoff. Otherwise it is AB or B depending on whether both can be in cutoff.

Bob

 

Class C if they can both be cut-off. Class B if one starts conducting at the exact moment the other stops.
class C is not used in audio (unsurprisingly), only in circuits with a resonant Load.

 

It's the conduction angle that defines class, not the type of output stage. This is elementary stuff until we get to digital “switching” classes.

 

Then there’s the dual power supply types - class G and H.

 

Audiofools anon., "Class H is like Class A, but a bit too open in the top"

https://www.chicagotribune.com/news/ct-xpm-1994-04-15-9404150249-story.html

Amplifiers are classified by using letters of the alphabet, denoting how they operate. Class A amplifiers usually deliver the best audio quality at the expense of efficiency. They consume enormous amounts of power even when not amplifying a signal.

It also costs a lot to build a Class A amplifier, with the more inexpensive beginning at $1,000 then soaring anywhere to $30,000.

Feeding the output transistors voltage less than full-time improves efficiency and lowers cost, with a slight sacrifice in audio quality. Engineers devised a multitude of ways to do this, in what is called Class AB.

About 80 percent of the amplifiers on the market are Class AB, which average about $50. Class B and C amplifiers create too much distortion for audio applications. The rarely produced Class D, known as a digital or switching amplifier, occasionally finds its way into an audio amplifier, though experts differ on the suitability of extremely efficient Class D for audio.

Engineers have also brought us Classes F and G, which average $1,200. Class H came and went, with its $950 price tag, falling just short of success.

But Technics engineers realized the potential of Class H and decided to perfect it, with its Class H+ amplifier delivering great sound with high efficiency. The Class H+ enables Technics to market a five-channel surround sound receiver for little more than a regular stereo receiver.

From Apr 14, 1994.
The hype never ends.

 

Modern audio opamps and power amplifiers are class-AB and the design reduces the distortion to almost nothing:

 

Modern audio opamps and power amplifiers are class-AB and the design reduces the distortion to almost nothing:

Except in certain op amps from Fairchild and National Semiconductor made in the 1970's. .

 

Actually, I think class D amplifiers are taking over now.

Bob

 

Rythm
And
Poetry

That's why it's called RAP!

When it is not poetry and not stuff that would be written and even the cadence is offensive then no, it is not music, but rather it is noise.
But the really nasty part about rap is that it seems almost universal that those who play it on sound systems appear to believe that all others should be forced to hear it.

 

My hearing aids have a setting with noise reduction that produces normal gain when a voice is heard. I use it when walking and if a car with blackened glass goes past me the RAP talker is blasting loudly but when he stops talking then the drums and the car backfiring sound levels are reduced until the RAP talker "continues talking to me".

 

He be talkin’ at choo, not to you.

Bob

 

I laugh whenever I hear a singer (who has pitch errors) being corrected with Auto-Tune software. Some of the new singers (there are many singers today who cannot sing in tune) have their Auto-Tune corrections difficult to detect.