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General Asylum General audio topics that don't fit into specific categories. |
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In Reply to: RE: You're welcome to believe what you pleas posted by E-Stat on July 28, 2018 at 21:08:46:
I don't know what to say . I feel like you will think I'm picking on you.
I am not. I am only trying to help.
A circuit is either Class A or it's not. It doesn't "reach" Class A.
** A side note to help clarify. It could be said that a Class A/B amplifier operates in "Class A mode" until it "reaches" the "Class B mode" and that would be an easy way to explain it to someone who's not technically inclined.
That being said, A Class A amplifier is Class A from the smallest output to the largest output it is capable of and then it totally falls apart. So there is no "reaching" Class A with a Class A amp. It just is Class A until it's over driven.
Figures 1 through 3 are showing the output of one of the two transistors in a push pull circuit when those transistors are driven by a sine wave.
Figure 1 shows the output wave form of a transistor that has no bias current (Class B) when driven by a sine wave. The bottom half the wave form is missing.
Figure 2 shows the output wave form of a transistor that has some idle (bias) current (Class A/B). The bottom half of the wave form is mis-shapen but at least there is some bottom half wave form.
Figure 3 shows the output wave form of a transistor that has full idle (bias) current (Class A). This is the idle current that it takes to get the transistor to give a bottom half wave form that looks as much like the top half wave form as the transistor is capable of. This is spoken of as running the device in as "linear a fashion as possible". Some books use the term that Class A is when you run the device only in the "most linear part" of the operating curve.
Another note for clarity, The more inherently linear the device is to start with, the closer one gets to the goal. With a triode vacuum tube the bottom half can look exactly like the top half (within limits). With a transistor, not so much.
P.S. Missing or mis-shapen wave forms or parts of wave forms = harmonic distortion.
I hope you take this in the spirit of good will. The spirit in which I intend it.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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Follow Ups
- RE: You're welcome to believe what you pleas - Tre' 22:32:12 07/28/18 (2)
- RE: You're welcome to believe what you pleas - E-Stat 05:30:17 07/29/18 (1)
- RE: You're welcome to believe what you pleas - Tre' 07:02:57 07/29/18 (0)
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