mfb said:
Electronics should be able to mimic this saturation effect, if the consumers like it.
They're working on it... Professional journal IEEE Spectrum got interested
http://spectrum.ieee.org/consumer-electronics/audiovideo/the-cool-sound-of-tubes
Solid-state designers have long attempted to produce tube simulators, using solid-state analog circuits like diode clippers and compressors to produce transfer functions and distortion akin to those of tubed guitar amps. Although these products have attracted only a limited following to date, the recent appearance of solid-state amplifiers based on digital signal processing (DSP) and using physical modeling algorithms, has stirred some interest among serious musicians.
And from
http://www.theaudioarchive.com/TAA_Resources_Tubes_versus_Solid_State.htm
Further reading explains in detail the effects that harmonics have on sound coloration:
" The primary color characteristic of an instrument is determined by the strength of the first few harmonics. … The odd harmonics (third and fifth) produce a "stopped" or "covered" sound. The even harmonics (second, fourth, and sixth) produce "choral" or "singing" sounds. The second and third harmonics are the most important from the viewpoint of the electronic distortion graphs in the previous section. Musically the second is an octave above the fundamental and is almost inaudible; yet it adds body to the sound, making it fuller. The third is termed quint or musical twelfth. It produces a sound many musicians refer to as "blanketed." Instead of making the tone fuller, a strong third actually gives the sound a metallic quality that gets annoying in character as its amplitude increases. A strong second with a strong third tends to open the "covered" effect. Adding the fourth and fifth to this changes the sound to an "open horn" like character. "
Now i'll digress on a personal theory , which pushes PF boundaries, but i'll show that it has some basis..
there's one effect I've never seen addressed in the hi-fi journals, probably i noticed it because of my fascination with electric motors.
A speaker is basically a motor. That it moves means it has dynamic response to voltage or current applied to it.
The signal applied to a speaker should be a faithful replica of the voltage applied to the amplifier input...
But should that replica be a voltage replica or a current replica ?
Because the speaker is a motor with inductance, resistance, inertia, as well as counter-emf from its motor action,
its impedance is complex meaning current through it and voltage across it will have different waveshapes - remember your derivative function.
Now - solid state amplifiers employ voltage feedback to make output a voltage that replicates input.
Tube amplifiers of the 1960's employ way less feedback, my Motorola SK47 console had around 10%.
Does a tube amplifier replicate its input with output voltage or with output current?
A pentode tube has high impedance, observe the flatness of pentode's current vs plate voltage curve...
from http://www.6moons.com/industryfeatures/zen8/zen8.html
The pentode tube output stage will do its best to deliver a current that replicates input voltage.
If one is testing the amplifier with an 8 ohm resistor load, of course the voltage developed will have same shape as current for V=IR and R is not complex. Tube and transistor amplifiers will look the same.
Replace the simple 8 ohm resistor load with a complex electric motor(speaker) and it's a different story.
Now V = IZ and Z includes jX
l and f(velocity), so the voltage and current waveshapes are no longer identical .
Exaggerating just a little, one might accuse a tube amp of being an ideal current source and a solid state amp an ideal voltage source.
Current sets the force applied to the cone, while voltage sets counter-emf hence velocity of the cone.
A speaker driven by a current waveform will not have the same motion as one driven by an identically shaped voltage waveform.
So the two amplifiers will produce different sound through the same speaker .
Whether the ear can detect the difference i cannot say. I was taught that the ear is insensitive to phase,
so only amplitude not phase of individual harmonics in the Fourier series would be noticed.One wonders whether this effect had anything to do with recent(to me anyway) standard for speakers to have resistance 80% of nominal impedance, to assure damping with low-Z
out transistor amplifiers?? Indeed better books on speaker design say to include amplifier output impedance, which is low for a voltage source and high for a current source.
Anyhow that's a personal theory and i apologize if it puts anybody off.. But here's the basis i promised at the beginning:
In an old PF thread i mentioned i'd once encountered a Dynaco solid state amp belonging to a local "Guitar-Zan" youth that employed feedback as all solid state amps do. But this one's feedback was measured from output current by a sampling resistor not from output voltage at the speaker terminal. Guitar-Zan described it as "Warm sounding".
Now three decades later i run across this regarding feedback in another Dynaco model, ST120:
http://www.updatemydynaco.com/documents/OriginalAmpModuleAnalysis.pdf
Page 5 of 5
© Daniel M. Joffe, 2011
It’s interesting to note that the feedback is actually current mode feedback, rather than voltage mode feedback. This is owing to the use of
the single transistor, Q1, rather than a differential pair.
I'd assumed Dynaco's current feedback was done to protect output transistors from shorted speaker wires
but maybe they had an ulterior motive ?
It'd be almost trivial to make a current sourcing amplifier
But i'd hear it as an engineer not a musician.
Anyhow -
today i learned I'm not the only one who's noticed current feedback in those Dynaco amplifiers that musical types so love.
And it's being noticed in engineering circles too.
http://www.edn.com/design/consumer/...periority-of-current-drive-over-voltage-drive
Loudspeaker operation: The superiority of current drive over voltage drive
Esa Merilainen -October 22, 2013
This is an overview of the destructive effects that voltage drive has on the performance of electrodynamic loudspeakers. A more comprehensive treatment of the subject can be found in the book
Current-Driving of Loudspeakers: Eliminating Major Distortion and Interference Effects by the Physically Correct Operation Method by Esa Meriläinen.
Today, practically all available audio amplifier and loudspeaker equipment works on the voltage drive principle without significant exceptions. This means that the power amplifier acts as a voltage source exhibiting low output impedance and thus strives to force the voltage across the load terminals to follow the applied signal without any regard to what the current through the load will be.
However, both technical aspects and listening experiences equally indicate that voltage drive is a poor choice if sound quality is to be given any worth. The fundamental reason is that the vague electromotive forces (EMF) that are generated by both the motion of the voice coil and its inductance seriously impair the critical voltage-to-current conversion, which in the voltage drive principle is left as the job of the loudspeaker.
maybe suitable for a thread in PFlounge ?
Ohhhh the curse of curiosity...
old jim
