From: bill.sloman@ieee.org   
      
   On 6/11/2025 2:39 am, john larkin wrote:   
   > On Wed, 05 Nov 2025 12:34:35 GMT, Jan Panteltje    
   > wrote:   
   >   
   >>> Bill Sloman wrote:   
   >>>   
   >>> But there's a difference between working well enough, and working really   
   >>> well, as I got to find out at Cambridge Instruments when I had to rework   
   >>> bits of the their GaAs single-crystal pulling machine because some of   
   >>> the parts had gone obsolete in  the ten years since it was first put   
   >>> together. There was a lot of bad design - or non-design - in the bits I   
   >>> had to modernise. It hadn't stopped the machine from making 95% of the   
   >>> single crystal GaAs pulled on the western side of the iron curtain.   
   >>>   
   >>> I invented my current mirror version of the Baxandall class-D oscillator   
   >>> to get a better sine wave source for the LVDT-based weighing system. The   
   >>> output amplitude was lot more stable than what we'd got from the system   
   >>> we had to replace. Nobody noticed. Getting rid of a 741 and its pop-corn   
   >>> noise was a lot easier, and that did get noticed.   
   >>   
   >> The 741 and 747 were not realy bad.   
   >> I designed an audio mixer that used the 747 back then used for sound in a   
   big hall,   
   >> got complements for the sound.   
   >> What sort of S/N level in dB are you talking about?   
   >> There is little difference in the 747 chip circuit diagram versus the 747,   
   >> the 747 has 2 extra diodes in series from output to the driver stage.   
   >>   
   >   
   > 741 was vastly better than the 709 or any such opamps.   
      
   It was a great deal easier to use. The 709 needed three frequency   
   compensation components and the input transistors blew up if you put   
   more than few volts between the inputs. The 741's performance wasn't   
   noticeably better.   
      
   Things like the uA715 had more bandwidth, the uA725 had more gain and   
   the LM308 had a higher input impedance.   
      
   The LM307 was National Semiconductor's equivalent to the 741. It was a   
   better part, but didn't sell anything like as well.   
      
      
   > GE made what was probably the worst IC opamp ever.   
      
   Part number?   
      
   > But the original 741s tended to have popcorn noise. Millliseconds or   
   > seconds of silence then a burst of offset pulses, hundreds of   
   > microvolts. It was caused by crud in oxide layers. Current production   
   > parts are probably OK.   
      
   And get packaged up and sold as 741 parts if they aren't.   
      
   Manufacturers test for pop-corn noise these day and modern data sheets   
   specify performance in the 1/f noise region.   
      
   > I like the OPA197.   
      
   Burr-Brown made nice op amps, but they were never cheap. I preferred the   
   Linear Technology parts.   
      
   --   
   Bill Sloman, Sydney   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)