kimbal Posted June 26, 2011 Posted June 26, 2011 I have interest in unconventional Tube Amp designs - not that conventional ones are bad - but because the unconventional are attempts to exploring things outside the square, regarding sound reproduction. ( Also I'm not satisfied with what everyone else has - I have to be different ! ) But to be fair - anything unconventional also has to be practical in order to be worthwhile. This matrix amp design I have never built, but toying with the idea; but before I do, I'm interested in others findings. I stumbled across the design on Steve Bench's site link below> http://greygum.net/sbench/sbench/1060amp.html After a careful study of it - it's nothing more than a 2.1 " surround sound " having 2 midrange- High frequency speakers and one bass speaker; making 3 speakers in the entire system. Correct me if I'm wrong, but I believe this is what is called " Dual single-ended operation". The main idea of the initial design of the 1950's was to cut costs in having a second Output transformer for stereo reproduction in phone-radiograms, with only using one pair of output tubes for stereo being required. The OPT was the most costly component and by having one instead of two, manufacturing costs could be reduced. In reality, it is nothing more than 2x SE tube output stages which work somewhat like push-pull Class-A in the low frequency band. On the bass end the Power output EXCEEDS the output of both channels driven as 2 single channels. This is the opposite and a very desirable charactersitic to any other amp of it's time. Around 1959/60 CBS studios, under the oversight of Norman Crowhurst, spent a lot of research on this design with some rather impressive results for a budget system. Like all audio sytems they have good and bad parametres - the bad ones in this system are not as bad as many might initially think - so the paper work says. I'm interested in anyone elses findings and what experience they may have had with this idea - since its in use today in solid state form as 2.1 surround sound. Steve Bench used an 813 version of the same amp 55w+55w/ch for a number of years as his main stereo. Instead of a specially made OPT; Steve used 2 conventional units with one acting as a parafeed arrangement. Not much point in my opinion, as it still uses 2 inductors on 2 separate cores, defeating the perpose of the original design. Since finding Steves website material I have unearthered some of Crowhurst papers on OP transformer design and stereo layout using a single bass speaker using this amp. The main differences this design has over a conventional amplifier with a single output tube and transformer, is it requires a third bifilar winding for the bass and two separate primary secondary combinations all on one core. Not that difficult when you study it in detail but initially it looks quite weird. After reading Crowhurt's papers I'm not so sure if Steve has understood it as well as he has described in his articals. His designs do work as th proof is in the results but it's a long way off what was originally intended. If any one wants the Crowhurst articals I mentioned, I can send it to you upon request.
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