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Original Message
RE: I've never heard one, do they sound that good?
Posted by Charles Hansen on October 10, 2010 at 10:43:36:
I still have the original Hitachi databook from 1977 with the suggested schematic, so I know it quite well. The circuit is very ordinary -- nothing unusual at all except for the MOSFETs.
The Hafler DH-200 is fairly similar although with one large difference. The Hitachi circuit is a conventional circuit, with the only complementary stage being the output stage. The Hafler circuit is fully complementary from input to output, as first exemplified by the Ampzilla (James Bongiorno) and later "the Leach amp" (as a construction article in Audio magazine by GIT professor Marshall Leach was popularly known as).
I'm sure that you can find used DH-200's for less than $200, and they would make a fine platform for modification. I think that the XL-280 would be even better, but they are much less common, probably more expensive, and have a JFET input stage that violates your "magic formula".
If you like the vertical MOSFETs, you may or may not like the lateral ones better. The lateral ones are much more linear and even lower in measured distortion. (You may need to parallel additional output devices to compensate for the lower transconductance.) The vertical devices are quite colored (due to their nonlinearities), but some people apparently like that sound. You may or may not be one of them.