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In Reply to: RE: The Magic and Mystery of Tubes posted by Madlove on April 17, 2016 at 09:21:04
"I'd love to study a diagram that shows in layman's terms the journey of the sound signal from needle to speakers. Has anyone done this?For instance, when the music signal hits the tubes, how is the signal affected, to sound warm or harsh or whatever?"
Well, to start with the music signal from the phono cartridge goes to ground across the grid resistor of the first tube. That's it, it's done.
That AC music signal voltage is present on the grid of the tube and that causes the current that's flowing in that first tube to increase (on the positive half of the music signal) and decrease (on the negative half of the music signal). You can think of it this way, the music signal on the grid of a tube is constantly changing the bias of condition of the tube causing the current that's flowing through the tube to increase and decrease.
When the current flowing through the first tube increases, the voltage drop across the plate resistor (the resistor between the plate of the tube and the power supply) increases so there is less voltage at the plate of the tube. When the current through the tube decreases there is less voltage drop across the plate resistor so there is more voltage at the plate of the tube.
When we strip away the DC voltage (by using a coupling cap) what's left is an AC signal that is like the signal that came from the cartridge but at a higher AC voltage. (this is amplification).
That larger signal will also go to ground across the grid resistor of the next stage (the next tube in the circuit) and cause that tube to change it's current draw across it's plate resistor.
So each stage recreates the input signal that it "sees" at it's grid.
The first stage "sees" the signal from the source (cartridge, CD player, ect.) but the second stage "sees" the signal that the first stage created caused by the source signal being present on the grid of the first stage and so on and so on.
The output signal of a stage will look very much like the input signal (only larger) if the tube is linear and if the tube is being 'operated' in a linear way. The "operating condition" of a tube includes the voltage from the plate to the cathode, the current running through the tube at idle and the total impedance* that the tube is playing into (* the value of the plate resistor in parallel with the grid resistor of the next stage.
When we get to the output stage of a circuit the plate load is an output transformer instead of a plate resistor and the output stage's job is to increase the current delivery capability so you can drive a loud speaker (current amplifier stage vs. a voltage amplifier stage).
If you get all the operating conditions of all the stages correct then the output of the circuit as a whole can look very much like the original input signal to the first stage (low harmonic distortion, little or no loss or exaggerations of the frequency extremes, etc.).
That was a very brief version of a very long story.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 04/17/16 04/17/16 04/17/16Follow Ups:
Tube Acolyte and Tre', thank you for the replies. I'm going to have to re-read them a few times, to get my head around it, but it seems very clear. I'll follow up on your info suggestions, looking fwd to it. Really great, thanks guys!
As to why, or how two identically functioning tubes affect music, don't think any one knows? but that they do is undeniable!
I suspect, since I lack an adequate understanding of it, that the root of the conundrum is our concept of what "an" electron is? Is it a nice finite little corpuscle of energy? One concept of light has that view.
Of course, the problem could be rooted in how an electrical signal jumps the synapse in my brain cells?
Tin Man bob
Never assume anything I post is accurate.
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