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What happened to class H amp technology????

I had a class H Soundcraftsman A5002 250 watt amp from 1983 and had it extensively modded in 1992. I ran it hard and it never never got hot. Just a tad warm. It was driving an Ohm I which could handle a 1000 watts continuous. After the mod the midrange became tubelike. The bottom end had a lot of weight . There was a slight edgy upper midrange that was irratating. I finally sold it and went on to Bryston. However I'm still amazed how it was able to drive near clipping for hours and not even at a strain. So my question is class H a viable thing in the future or is it forever obsolete. It wasn't a bad amp compared to Bryston. Thanks for any responses especially engineers. Mike
128x128blueranger
blueranger's avatar
blueranger OP
575 posts
 
Also one thing that swayed my opinion in buying the Soundcraftsman was the Julian Hirsch  review in Stereo Review. I quote "it's as good as anything else I've tested". 
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bombaywalla's avatar
bombaywalla
1,957 posts
 
blueranger,
class-G/H amplifier technology is alive & well. ARCAM, the British brand, offers several amplifiers using class-G topology such as this one:

http://www.arcam.co.uk/products,FMJ,Integrated-Amplifiers,a49.htm

i'm sure they have more products if your search their portfolio.

in class-G what they do is that they switch in a 2nd, 3rd, 4th power supply of progressively higher voltage levels as the amplitude of the music signal gets progressively higher. The key is to switch in the higher voltage level power supply only on-demand. When not needed, these additional power supplies sit idle consuming just a low amount of bias current. That's why your amp never got hot. Also, when the additional power supplies were switched in, more output devices are also switched in under the assumption that more load current is needed at higher voltage amplitude levels. Thus the output impedance of the power amp remains essentially the same i.e. damping factor is maintained.
Class-H is an extension of class-G. in class-G they have a discrete number of additional power supplies while in class-H they have an infinitely variable power supply rail.
ARCAM must have figured out how to avoid getting a glitch on the output voltage when a power supply is switched in/out. Needless to say having a glitch on the output waveform would have increased distortion many fold & in audio that would have been unacceptable.
So, the biggest con for class-G/H is that it's expensive to engineer & hard to perfect thus very few manuf offer this topology in their product offerings.  



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