e4d8f4fe   
   From: info@turneraudio.com.au   
      
   > But she's been unable to focus much on her audio hobby   
   > interests because of her heavy committments to well paying job at a   
   > university.   
   >   
   > ** The uni's workshops must be where she gets all that nice metalwork and   
   > cabinetry done.   
   >   
   >     Foreign orders anyone ??   
      
   I doubt it. Unfortunately, perhaps you don't know Susan as well as I   
   do, and bearing in mind your own difficulties with females and your   
   sprinklings of negativity I can only smile at your comments, and I   
   hope in that in the fullness of time you would find a wealth of   
   personal pleasures to be had where you wouldn't dream of dissmissing   
   so many people because you can gain access to their wit, their   
   determination to genuinely discuss things, and other wondrous facets   
   of human bevaiour so that you benefit as they might, without duress,   
   or verbal scaldings of boiling oil when there are inevitable   
   dissagreements, as indeed there must be for any of us to attain   
   wisdom.   
      
   Well you may complain about the costs of building a minimamlist   
   amplifier with just an input tranny and output tranny and 2 N mosfets   
   in source follower mode and class A. Ah, but the cost you say -   
   hopeless silly effort. Indeed cost is high, but all hobbies are all a   
   waste of time and money when that time and money could be put towards   
   fine charitable causes, or medical research, or R&D for a company   
   wanting to make 1 square metre solar panels that are 50% efficient for   
   $2 each, with lightweight batteries to go with them. Surely the   
   persuit of listening to music with valve amps is a true monumental   
   waste of human resources, and you'd prefer them all to beat a path to   
   your door to get advice on how to make an amp for $3, weighing less   
   than 100 grams and 99% efficient. Of course that's exactly where the   
   audio industry had headed with PWM amps fed by digital audio signals,   
   so the world beat you to it. Its another huge tragic waste that the   
   world wants 6.1 home theatre, with screens 10 feet wide and suburban   
   houses which compete with those owned by Louis IXV, and of course   
   everyone needs 2 cars each and they want to each eat enough to feed a   
   family of 16 Africans, and only vote for parties that give out yet   
   more Guvvy assistance. They then spnd hundreds of thousands on   
   expensive messy acrimonious divorces, and while learning nothing,   
   repeat it all. So I see your point in complaining about the cost of   
   Susan's minimalism approach. Don't worry, she more than compensates by   
   not having children and living a very simple life while owning a push   
   bike, while battling on in a maddening world.   
      
   I'm left wondering also about what became of your website? Where has   
   it gone? But then it dawned on me that perhaps you never got around to   
   inviting the world to your mind, so they may see how good audio could   
   be achieved. Was it all too vain and selfish to make a website? That's   
   a real pity considering you have vast knowledge. Nobody I know, except   
   possibly someone who might be your twin, would frown on having a   
   website.   
      
   In 1990 I frivolously built a pair class A amps with 4 mosefts with an   
   OPT. Mosfets are driven by LTP with 2 garden variety bjts in LTP and   
   one for a CCS. It has cap coupling, and works just fine, and gives 40   
   Watts in class A with THD < 0.3%. I've never found anyone to say it   
   sounds worse than a tube amp with 4 x EL34 etc, and one may wonder why   
   I made these things but I enjoyed the experience and it taught me   
   more. One of these days I may convert it to Circlotron and have a pair   
   of EL84 as input/drivers, but I may never find the time.   
      
   Susan's amp has a step up input tranny with 600 ohms impedance. The 2V   
   input must be raised to roughly 30V output for gate to gate drive, and   
   to get input Z = 600r, the sec load must be 136k, and if Sec C load =   
   100pF, then Cin at Pri = 0.022uF. I'm guesstimating here but HF roll   
   off would trouble many people unless thay had a very low drive source   
   powering the IPT and if they didn't have a decent IPT.   
   Sue just uses a power mosfet as source follower to drive the IPT. The   
   lower the drive source Z, the less the characteristics of IPT and OPT   
   will cause distortions. Of course many say its a waste, but it matters   
   not, and the status quo is stained by productions governed by   
   accountants, and anything other than what mainstream industry does   
   becomes invalid.   
      
   Anyway, using a pair of EL84 in triode with Ra = 2k5 to drive perhaps   
   50pF of input C at gates seems a reasonable solution. Having mosfets   
   in circlotron with simple OPT means you have matching devices, and if   
   Vds on each mosfet is 20Vrms, then gate drive = about 10.5Vrms Vg-0V,   
   and the amp Rout is low enough and because class A, and ß = 0.5 and   
   open loop mosfet A = about 20, then THD is low, bandwidth vert wide,   
   and so you get hi-fi, fairly simply, without GNFB, or an IPT. The OPT   
   is probably best if an auto tranny, and can have 8 ohms input end to   
   end for 50 Watts of output with 20Vrms. If OPT core = 50mm stack of   
   50mm tongue E&I with partial air gapping for µe = 3,000, then wire   
   size is large and its quite easy to wind. On each side of PP circuit I   
   think a good load is 32 ohms for each of 4 class A mosfets, so that   
   all four drive the OPT primary of 8 ohms. Taps for 4 ohms and 2 ohms   
   are easy but I'm still not sure of HF performance because with say 2   
   ohms, using 1/2 the total auto tranny turns, the leakage inductance   
   affects the HF pole.   
   I'm trying to figure out a decent winding set up that allows many Z   
   combinations so as RL is lowered, the class A action remains and the   
   amp doesn't move into class AB.   
      
   There doesn't seem to be very much online about making audio auto-   
   trannies with very low winding losses and HF losses for Z range   
   between say 1 ohm and 64 ohms. Having an auto tranny which gave say 64   
   ohms to 4 ohms would be a boon to owners of tubed OTL amps. They tend   
   to become dissolutioned by OTL tubes suffering bias failure from   
   overheating due to the inevitable very poor load matching even with   
   multiple 6C33c output tubes. The load line analysis I've done on 6C33c   
   indicates good class A is available if Ea = +160V and RLa = 250r, and   
   Pda = 60W with Ia at around 370mA. 4 such tubes in class A can give   
   40Watts, and OPT primary RL can be 62.5 ohms. To my mind, this is   
   superior to using the same tubes hooked directly to 8 ohms and forcing   
   tubes on each side of PP circuit with low bias, and in class AB2, to   
   each produce say 1.4 amp peak current. 40W into 8 ohms is 3.15 peak   
   amps, so at least 6 x 6C33c are wise, and Pda with continuous signal   
   invites smoke, and things get worse with 4 ohms. Auiophile say they   
      
   [continued in next message]   
      
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