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In Reply to: Amity Amplifier posted by chrismercurio on November 8, 2011 at 08:16:20:
I started building the Amity since year 2000 and has made some changes when Lynn Olson (nuthifi) website updated toe circuit (since the Amity circuit has changed frequently between Y2K and 2006).
The amplifier requires tremendous amount of gain and voltage from preamp, you have to make sure your preamp has enough gain and voltage for this amp. To make you safe, better above 25db of gain from your preamp and the output voltage is high enough.
NO matter which version of Amity, it needs both high gain and voltage from the preamp. I finally go to the Karna, yes, it sounds better. Smoother and more drive to the sound, and dynamic contrast is improved. However, one thing I don't agree with Lynn Olson is putting 300B push pull amp and mate with very sensitive horn speaker. It sounds a bit edging on several different horn systems (from Western Electric type to Homebrew electromagnetic system). Maybe his Avangarde behave differently.
However, I insists a good 300B / KR300XLS in SE type circuitry after so many years of work on DHT push pull. But I never give up, still working on a high power push pull amp with group of my friend, well....211 at the output this time.
Back to what you're asking, how it the Amity sounds like. The Lynn Olson Amity can behave like a good SE amplifier in few areas, such as quickness, transient speed and clarity, this is a lot do to the transformer coupled. However, it has better dynamic range than the SE, but no free lunch, the push pull circuit kills the "immediacy" that I really enjoy with the SE amplifier, especially low power 300B or PX25 or even 45!!!
I have came across so many different 300B and other DHT push pull from manufacturers around the world, it can be a Cary 211 PP, Chinese made MingDa, World Audio Design (designed by Andy Grove for HiFi World magazine) transformer coupled 300B kit , Uesugi 300B, VAC Renaissance series 300B that received highest praised from TAS HP during 90s, etc.
Not many 300B push pull sounds really good, and one of the best sounding 300B push pull is the one from Scandinavian called LA audio (LA is the initial of the designer name, not Los Angeles) that has toroid output transformer!!
Few things you have to consider before building the AMity or Karna, the part choice that Lynn Olson settled is for his system and doesn't mean will work on yours. A proper power supply capacitor choice, interstage transformer and output transformer for the Amity or Karna should be caution. The Lundahl amorphous irons is pretty good, and I have tried their phase splitter input transformer couple years ago for my 211 push pull project with great result. I like the sonic character of both Hashimoto output transformer and James interstage transformer. As far as power supply capacitor, you should go for either Continental type A or Blue Line cap from ASC. But you won't go wrong by having all the way Lundahl amorphous core!!
In conclusion, all I can say a well designed KR300BXLS driving by WE 437A via transformer coupled with 2 x 300B or 274B as rectifier blew away the 2 x 300B in push pull circuit. Unlike a decade, it has pretty efficient loudspeakers existed nowadays for low power SE type, take a look at the electromagnetic type horn system.
THis is 100% personal opinion.
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