The Class-H amp and

rtarbell · 21st February 2006, 04:17 AM

I've been keeping up to date on the recent thread about class-h amplifiers, and I wanted to ask a question that I've had for a long time. I know there exists different terminology, so let me state that by class-h, I mean an amplifier where the power supply rails track the output voltage continuously (NOT a rail switching amplifier).

I understand that the class-h amp is often a class-D amplifier set to high efficiency that surrounds a class-AB conventional amp. How can we be sure that the propagation delay over all audio frequencies of interest will be the same? For instance, let us say that we have a spike on the output of the amp (a sharp increase, followed by a sharp decrease).

==> If the class-D amp does not react in time, then the output transistors of the class AB amp will go into saturation on the positive increase (due to the supply rail not increasing as fast as the base voltage at each NPN output device).

==> If the class-D amp reacts too fast, saturation again as the rail will already be on its way down before the base voltage on the output devices of the class AB amp ever completed their increase.

==> How is this problem addressed in successful class-h amps?

Tim__x · 21st February 2006, 05:48 PM

Even the largest music transients don't slew all that quickly. 100w into 8ohms at 20k requires 5v/us, so as long as you keep 5 volts of headroom for the linear stage a uS of mismatch is acceptable.

21st February 2006, 04:17 AM	#1
rtarbell diyAudio Member Join Date: Sep 2005	The Class-H amp and I've been keeping up to date on the recent thread about class-h amplifiers, and I wanted to ask a question that I've had for a long time. I know there exists different terminology, so let me state that by class-h, I mean an amplifier where the power supply rails track the output voltage continuously (NOT a rail switching amplifier). I understand that the class-h amp is often a class-D amplifier set to high efficiency that surrounds a class-AB conventional amp. How can we be sure that the propagation delay over all audio frequencies of interest will be the same? For instance, let us say that we have a spike on the output of the amp (a sharp increase, followed by a sharp decrease). ==> If the class-D amp does not react in time, then the output transistors of the class AB amp will go into saturation on the positive increase (due to the supply rail not increasing as fast as the base voltage at each NPN output device). ==> If the class-D amp reacts too fast, saturation again as the rail will already be on its way down before the base voltage on the output devices of the class AB amp ever completed their increase. ==> How is this problem addressed in successful class-h amps?

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21st February 2006, 05:48 PM	#2
Tim__x diyAudio Member Join Date: Jun 2004 Location: Edmonton area, Alberta	Even the largest music transients don't slew all that quickly. 100w into 8ohms at 20k requires 5v/us, so as long as you keep 5 volts of headroom for the linear stage a uS of mismatch is acceptable.