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Monday, November 2, 2015

De-mystifying a chip -- Looking inside the 741 Op-Amp

Inside a 741 op amp, showing the die. This is a TO-99 metal can package, with the top sawed off
Inside a 741 op amp, showing the die. This is a TO-99 metal can package, with the top sawed off

This is really cool and potentially life-changing for radical fundamentalist ludite homebrewers.  As our readers will know, my big objection to the use of integrated circuit chips is the fact that these little black boxes are in fact often, well,  little black boxes.  We don't know what is going on in there.  It seems to me pointless to shy away from the use of large black boxes (the extremely complex "radios" that dominate the amateur airwaves today) only to fill our homebrew rigs with smaller black boxes. 

But when we crack one of these boxes open and take a look at the transistors, resistors, and capacitors formed on the substrate, then diagram it all out,  I think the fog of mystery is blown away by a refreshing wind of insight and understanding.  We saw this happen on a much smaller scale when someone cut open an SBL1 mixer, but that wasn't an IC.  Ken Shirriff has now done this with the venerable 741 Op Amp.  And he did it with a hack saw.  Bravo Ken.  I can now in good conscience uses 741 op amps in my rigs.    



  1. It's all the same physics as galena detectors, condensers and lacquered inductors! Just a bit smaller and a bit cleverer... And there's nothing to stop you building your own equivalent chip out of discretes - see http://spectrum.ieee.org/geek-life/hands-on/build-your-own-giant-555-timer-chip


  2. Looks like manhattan construction in there too! I'm OK with ICs as long as they are readily available and cheap. Then you can buy a few for spares or future enhancements.

  3. If you've really mapped out the internals of the 741 - and drawn a circuit diagram from that - compare that to the diagram published in the spec sheet. If they match, you can quite confidently assume any IC's spec sheet will likewise tell you what the internals are. As you investigate the more complex devices, the sheets themselves become collections of 'black boxes' (block diagrams), but the principle remains. Use the Data Sheets - they can de-mystify.
    In the '80's I built a stereo using 4 discrete 741's, each within 10x10 holes (1"sq!) of Veroboard. These stood on-edge to the main (again Vero)board, becoming themselves "IC's".

  4. If this interests you look at Chris Tarnovsky's work. https://en.wikipedia.org/wiki/Christopher_Tarnovsky

    Watch any of his videos from the hacker conferences and you will be pleased.

    Life changing, huh? ok.


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