Re: gEDA-user: A little puzzled about the purpose of gschem

[Gene Heskett <gene.heskett@xxxxxxxxxxx>]

On Wednesday 28 April 2010, Dave McGuire wrote:
>On Apr 28, 2010, at 3:40 PM, John Doty wrote:
>> Well, you started out complaining about a 741 model. I'd call that
>> a very rare, obsolete part: I haven't actually seen one in a
>> circuit in over 30 years. I guess it's still in textbooks (read
>> Stephen J. Gould's rants about textbook authors' tendency to copy
>> from previous textbooks sometime), but why would anyone use it in a
>> new design?
>
>   Very rare?!  I see 741s everywhere.  WTF?
>
>              -Dave
>
Sorry to bust the bubble, but he's right.  The 741 is well over 40 years old, 
and its open loop first response pole, where the 6db per octave rolloff 
begins, is a measly 10 hertz.  Today there are $1.00 opamps with a working 
gain of 20 when feedback is applied, with output slew rates of several 
thousand volts per second.  Thats working bandwidth to several hundred 
megahertz at the sort of levels found in either a modern broadcast audio 
mixer, or a production video switcher, and either of those are driving 60 
ohms for audio, or 75 for video.

Slew rate limits alone in the 741 means you can't honestly ask it for more 
than a volt of output at full audio bandwidth.  At 3 volts the slew rate 
distortion is so bad even these 75 year old ears can hear it.  Even a TLO-72 
or 74 can mop the floor with a 741, and output a +- 15 volt rail to rail 
signal doing it, but into the old 600 ohm std load.

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
"The only way for a reporter to look at a politician is down."
-- H.L. Mencken


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