dynamic loadline

[Stefanoo]

Hello to everybody,

I have problem to figure out the exact meaning and mathematical construction of the dynamic loadline.
All the information that i found over internet are under payment (i mean i have to buy them).
The books that i have are not very clear over this subject and so i ask for your help.


hope somebody can give me some usefull link where to download informations.


Thanks in advance.

Regards,
Stefano.

[EC8010]

A resistive loadline is a nice straight line, and could be called static. A loudspeaker is very rarely resistive and will cause the loadline to depart into an ellipse. You could call that dynamic. There are exotic waveforms (bearing little relation to music) that can cause loudspeakers to draw even larger currents than would be suggested by their complex impedance. These would certainly be called dynamic.

[Stefanoo]

thanks for the explanation.
Now i understand that is the deviation from the resistive behaviour that leads to distortion (if i haven't understood wrong).

What i need is the mathematic explanation e construction and some other detailed information.
I'm sure there are information but as i said, those info are not free.

[lndm]

With general regards to loadlines, a place to start might be to learn to draw them for the single ended common cathode amplifier stage. Here is one tutorial http://www.tubecad.com/articles_2003..._Amplifier.pdf
if I have understood correctly

[EC8010]

You can construct a dynamic loadline by first plotting the resistive element in the standard way, then calculating the peak current drawn by the complex element of the impedance at your chosen frequency and output voltage, subtracting and adding this to your quiescent current to give two further points. Then draw an ellipse to go through these points and the peak voltages you chose. It's usually a bit of a waste of time because it would need to be done at a number of frequencies to show anything meaningful.

It is far better to use an active crossover and add a Zobel network across each loudspeaker to cancel the inductive component, then only drive each loudspeaker above its resonant frequency, thus seeing each loudspeaker as a resistor...

[Stefanoo]

well i know how to draw a static load line, of course.
The point is that i don't understand the exact meaning of the dynamic loadline neather do the sense of that.
What can i see trhough a-c load line?
I'm interested to see how MATHEMATICALLY the a-c load line is built.

I can't find anything enough clear that helps!

I'm looosssttt.....help me please !!!

[EC8010]

The use of an AC loadline is that it allows you to see how reactive a load you can drive. If your load is of the form Z = a + jb and V is your maximum peak output voltage, then peak reactive current = +/-V/jb. Plot these excursions from your quiescent current (no voltage swing at this point) and you now have four points of your ellipse, which is the AC loadline for your chosen frequency and output voltage. Now look at the ellipse and see if it crosses through anywhere unpleasant, like the negative resistance region of pentode curves, Vg = 0, or (worst) Ia = 0...

[Stefanoo]

where did you get this information from?
Do you have any helpfull link with pictures and formulas?
Or, could you refere me at any good book that covers this issues?


Thanks

[zigzagflux]

If you are interested in the equation for an ellipse, then it is (x^2/a^2) + (y^2/b^2) = 1, where 2b is the minor axis, and 2a is the major axis.

Basically, if you fit a rectangle just outside the bounds of the elllipse, the height and width will be 2b and 2a.

May the Good Lord help you if you actually want to use this equation, or if you attempt to correlate a speaker to this equation (make it fit).

That's what they make curve traces, trial and error, and experience for.

[Stefanoo]

well......actually right now i'm studying the theory of the tube's amp.
I read a 3-4 books by now and just yesterday i found this dynamic loadline.
honestly your word confused me even more.
I know what an elliplse is and its equation (i'm an electronic enineer).

I just would like to find a clear book that would explain as well as the static load line is usally explained everywhere.
The sourec of infometion that i got don't consider this subject very clear!

first i don't understand why the loadline has to pass trhoug the bias point.

I've just proved the following equation:

given a load zb=rb+jxb
sinusoidal plate current ip=Ipm*sin(wt)

the plate voltage: ep=-ip*zb

ep^2 + 2 * rb* ip * ep + mod(zb)^2 * ip^2= xb * Ipm^2

which is an ellipse with origin on (0,0) so i don't understand how it can pass for the bias point.

But then, from here, i don't know how to move over and match this with the static tube characteristics, what has to do with the distortion and i don't know, mainly, what it represents exacly in the contest of an amplifier stage ....and so on and so forth.


Hope to clearify this point.


Regards.


P.S. i see that you are from milwaukee...my wife is from wisconsin (oconomowok WI)...and i've been to milw last summer....i've been to a jazz festoval there....it was super nice.....the only thing...in wi...they pretend to imitate too much the italian food...and they are not able to get it all the time