From: info@turneraudio.com.au   
      
   On Tuesday, 8 November 2016 01:52:50 UTC+11, sadlif...@gmail.com  wrote:   
   > Build OTL = transistor   
   > P: 65W   
   > Vin: 0.775V   
   > Rin: 400 kΩ   
   > BW: 30Hz - 17kHz   
   > 0,2%   
   > CMRR: 70 dB   
   >    
   > i don't know where to start. Help me please :(((   
   >    
   > Thanks a lot   
      
   This is a tube based discussion group. But some ppl who have been here since   
   about 1995 don't mind solid state, aka Squalid Stait. There used to be   
   magazines with details for kits you could build for SS, but the Internet   
   killed mags and Pulse Width    
   Modulated amps with solid state and circuit boards so tiny and complex there   
   is nothing for a DIYer to do.   
   Nevertheless, a DIYer can build a very good class AB amp if he sticks to all   
   discrete parts. In 1996 I made a stereo amp with BF469 and BF470 for   
   input/driver, and 6 x npn and pnp mosfets 2SK1058, 2SJ162 for output. It can   
   make 350W per channel with +/-   
   65Vdc rails. THD at 200W < 0.01%, noise with no signal < 0.25mV, so fet inputs   
   are not needed.   
   I've also used bjts  for output stage but I loathe them because they are so   
   much more difficult to stabilize, and suffer cross conduction above 10kHz.    
      
   If you do not want to learn about how all the devices devices work and just   
   want to build a box with pre-made modules, then be prepared for smoke and   
   silence after you turn it on. buy 4 modules. This allows you to fry two then   
   maybe you learn why - and    
   you have two spares.    
   The sound you will hear after you have labored long and hard for 3 month's of   
   sundays might be OK, but maybe it won't be as good as a decent tube amp with   
   OPTs. Probably, you do NOT NEED 65W capability. Nobody I ever knew during 19   
   years in audio trade    
   ever needed average power of each channel above 0.5W. If they turned up level,   
   their wife & dog would leave.    
      
   At least you are not trying to make a tubes OTL amp which IMHO is a pathway to   
   sonic bullshit. Men like to believe the sound is better without an OPT but its   
   a complete myth. DIYer construction of a good OTL is prone with all manner of   
   difficulties. One    
   involves buying at least 10 x 6AS7 for each channel for maybe 50W max, and   
   then having to pay high electricity bills.   
   2 x KT88 in UL mode will sound better than any tubed OTL horror.    
      
   If you wish to learn all you can learn, you need to build a preamp using say 1   
   transistor. Yes, just ONE. PN100 will do. Then you build and READ about bjts   
   from old books, and not jerks online with much to say but nothing about how   
   basic stuff works.    
   Learn & Build needs you to get the gear such as oscilloscope, volt meters,   
   function generators and ability to make a hand made circuit board and how to   
   make a safe PSU - the ONE transistor preamp make take 6 weeks because each   
   step of the way provokes    
   questions you must answer yourself. The single BJT won't be perfect, but its a   
   start. Opamps have dozens of bjts within and you can't ever understand basics   
   with them because you don't yet have any idea about gain of devices, the NFB   
   and many other    
   things.    
   I've said too much, again.    
   The 2x300W stereo amp I made sounded just as well as a class A tube amp   
   capable of 50W pure class A with 4 x GE6550A per channel. I had 4 blokes over   
   one evening for listen session, and I switched to SS amp after an hour with a   
   switch I'd rigged up. They    
   were ALL fooled, not one perceived any sound change. When I owned up to this   
   mean nasty trick, they were not happy, but one said, "well, the same bastard   
   designed both amps, so I guess they both sound just as good..." The lynching   
   rope was put back in    
   the bag.   
      
   Hardly anyone is building any sound gear at home now. The GFC in 2008 lowered   
   standards of living in USA, guys who were self reliant got old, and the   
   Internet and smart phones seem to be making a whole generation quite dumb, or   
   lazy, or dumb and lazy.   
   Patrick Turner.     
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)