Originally Posted by bing!
I watch this to 27minutes, it's getting very technical into the internal design of the DAC, the difference between R2R and he called PWM. How the R2R has the max number of FET switching from slightly negative to slightly positive. That's true. But it's not very useful for what we are interested because we have no control how the IC was designed. I kind of called it for the day. Sounds like he actually design circuit, FPGA and write codes for Noise shaper etc. this is really not my interest.
But he talked about the small signal non linearity is of my interest. This mean the gain change some in very low level signal region and that hurts the perception of depth. This is very interesting. I understand what that means in terms of DAC. But I can use this to look at power amp also.
In power amps, most are of Class AB unless you are willing to burn a lot of power, put up with a lot of heat, then go Class A. Class AB amps ALWAYS have crossover distortion when one side of the push pull output transistors turn off and the other side turn on. That's when the driving is handed from one side to the other side. The transition is NEVER smooth, that's crossover distortion
. We know crossover distortion is a major problem and different ideas are used to minimize or eliminate it.
The easiest is to go Class A, there is no crossover distortion as both side of the transistors never turn off and there is no hand over.
Class AB always has crossover distortion. The way to minimize the effect is to increase the bias. Increasing the bias increase the region where both sides stay on longer, increase bias increase the region where the amp behaves like Class A. As the video said, it's the low level signal distortion that is very important, so the higher the bias, the higher the output signal before the amp goes into class B. The larger the signal, the less important is the distortion.
Like if you use 1A bias current, that will give you the first 16W output in class A driving 8ohm speaker. So in most cases, it's a class A amp. So the higher the bias, the better.
That's the reason NOT all amps are the same as long as it's not clipped. It's the crossover distortion that affect the depth perception. To have high bias, you need more output transistors, bigger heatsink. That's the reason I always talked about literally first line judging at how good an amp by looking at how many output transistors and how big the heatsink.......how heavy the power amp is!!! There is NO WAY out of this one. Output power is totally irrelevant as long as it's not clipped, a 200W amp can sound lousy and a 50W amp with good design can sound a lot better. You don't judge the quality of an amp by the power.
I dont' know how true is the relation between small signal linearity and dept perception, it makes sense. More importantly, most high end amps use big heatsink, many pairs of output transistors and good power supply. There are very good reason for that.