Transitional Miller Compensation (TMC) vs. Two Pole Compensation (TPC)

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#41
Bonsai said:
I regret to say, my opinion on this has changed. I settled on TMC not long after posting the above. The HF peaking you get with TPC requires heavier front end filtering if you want a perfect square wave response. Quite how Syn08 [RIP] or anyone else can claim they are equivalent is beyond me and especially given the comments in post #26 above. They both extend the loop gain bandwidth, but in practice, their behaviour is less than equivalent given TPC’s peaking problem.

Re post #26 above, what if the max current available to charge the VAS comp cap is not limited by the tail current as it is in a VFA?
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Compensation is topology dependent, pivotal around this is the zobel. Closed loop as well as open loop behavior dictates stability. Especially when using Cherry one cant put base stoppers all over as some of these may cancel out with Cherrys behaviour, you just need to know where to put them and where not to put them
 
#42
There are two issues to deal with here, although one can trigger the other in some cases (Cordell mentions this as well):-

1.Oscillation due to loop gain/phase issues
2. Parasitic oscillation

In most designs you would have to fix #2 as a matter of course before you can do a proper job on #1 and in an EF3 triple will almost certainly involve base stoppers. These use low-value resistors in the driver and output device bases (John Curl spoke about using 10 Ohms) and the pole associated with the device base capacitance is high (MHz) and well away from anything that would influence the loop poles materially in a correctly compensated amplifier. The base stopper poles at that stage are very much lower than 0dB and >> the ULGF.
 
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#43
Most designers including myself focus on designs that do 100khz square operating the design on the verge of instability, higher bandwidth also exposes an amplifier and listener to some more unpleasant surprises. Setting the range of human hearing as 10kHz , an amplifier that faithfully reproduces square waves at 40kHz has sufficient bandwidth making an amplifiers bandwidth higher than this introduces complexities of noise pickup and additive high frequencies that sum into the audible range. In the digital ream for audio sampling 96kHz is good enough for even the most discerning listeners
 
#44
OnAudio said:
TPC+Cherry also named OITPC by Dadod displays potential for oscillation. Unless all parameters are fed into a simulator it won't catch some oscillations. Some of this instability is waiting for a cymbal strike or a metal track, when cymbals don't sound like cymbals or metal sound as metal. When a class AB amplifier sounds like a class D amplifier, then its likely its oscillating, the difference being that class D is controlled oscillation
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I built a number amplifiers with OITPC with no oscilation problems. Have you built any?
Some of DIYers have built also and no complains with the sound quality .
If you came to this conclusion only from simulation it's not good enough.
 
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#45
Dadod, Bonsai, while we may not during testing visit all possible states of the circuit, here's a small diagram to reason with. Note however there is no claim that an amplifier using your scheme will necessary oscillate in the wild, we don't know
funcky phaser.png
 
#54
#56
Compensation is very amplifier specific, most amplifiers will need just 1 cap to stabilize them, others require multiple caps to stabilize, some of the caps can also be eliminated by using lower ft and lower hfe devices, even cob can be exploited, heres an example of my designs using industry agreed standards for compensation
https://www.pcbway.com/project/shareproject/SYMEF_Audio_Power_Amplifier_8bb70aa8.html
https://www.pcbway.com/project/shareproject/SYMPHONY_audio_power_amplifier_f05686aa.html
https://www.pcbway.com/project/shareproject/SYMEF_Ensemble_audio_power_amplifier_bf5439e4.html
https://www.pcbway.com/project/shareproject/Orchestra_audio_power_amplifier_20a20a77.html
https://www.pcbway.com/project/shareproject/Morpheus_audio_power_amplifier_61fe3f69.html
 
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