Yes it would be dirtier..
First off let me state that when an amplifier adds parts to or removes parts of the input signal, that is distortion. Since the transistors in class C amps conduct less than 180 deg. of the full waveform, the clipping of the waveform (missing parts) is a big part of what causes the distortion. If you take a sine wave, as an example, and clip better than half of it, you only get part of the original waveform back, (and a small part at that) but the points at which the wave is clipped form sub-waveforms that are at multiples of the original frequency. This is harmonic distortion. When you increase the bias current and/or voltage, the transistor begins to reproduce more and more of the waveform until, with class A amps, the full input waveform is reproduced exactly. This is the best possible design, since there are no missing parts of the waveform, but requires the most current.
Typically, what a conscientious operator wants is full power, with the least amount of trash (spurious emissions like harmonics and splatter). This is easily obtained with properly driven class A circuitry. Even with class A though, if you overdrive the amp it will cause distortion just like class C amps. Class B amps are dirtier and more efficient than class A by a large margin, but they are cleaner than class C. Class AB is a compromise between class A and class B, resulting in a good balance between cleanliness and efficiency.
Now my understanding of IMD is a bit limited, but as I understand it when a transistor passes the threshold between it's "off" state and it's "on" state (the point at which it starts conducting), at that instant the transistor's output is not always perfectly faithful to the input waveform. I think of it like what happens when you flip a switch. Often there is a spike of power at the instant the switch engages. This is more pronounced when there is a lot of current involved. When there is a large signal entering a transistor, every time it switches on (which happens every cycle) a tiny spike is generated. This train of spikes becomes it's own signal superimposed on the main signal, which is distortion. IMD is much less of a problem at low drive levels, and becomes a BIG problem when an amp is overdriven.
First off let me state that when an amplifier adds parts to or removes parts of the input signal, that is distortion. Since the transistors in class C amps conduct less than 180 deg. of the full waveform, the clipping of the waveform (missing parts) is a big part of what causes the distortion. If you take a sine wave, as an example, and clip better than half of it, you only get part of the original waveform back, (and a small part at that) but the points at which the wave is clipped form sub-waveforms that are at multiples of the original frequency. This is harmonic distortion. When you increase the bias current and/or voltage, the transistor begins to reproduce more and more of the waveform until, with class A amps, the full input waveform is reproduced exactly. This is the best possible design, since there are no missing parts of the waveform, but requires the most current.
Typically, what a conscientious operator wants is full power, with the least amount of trash (spurious emissions like harmonics and splatter). This is easily obtained with properly driven class A circuitry. Even with class A though, if you overdrive the amp it will cause distortion just like class C amps. Class B amps are dirtier and more efficient than class A by a large margin, but they are cleaner than class C. Class AB is a compromise between class A and class B, resulting in a good balance between cleanliness and efficiency.
Now my understanding of IMD is a bit limited, but as I understand it when a transistor passes the threshold between it's "off" state and it's "on" state (the point at which it starts conducting), at that instant the transistor's output is not always perfectly faithful to the input waveform. I think of it like what happens when you flip a switch. Often there is a spike of power at the instant the switch engages. This is more pronounced when there is a lot of current involved. When there is a large signal entering a transistor, every time it switches on (which happens every cycle) a tiny spike is generated. This train of spikes becomes it's own signal superimposed on the main signal, which is distortion. IMD is much less of a problem at low drive levels, and becomes a BIG problem when an amp is overdriven.
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