Welcome to 2017. This blog is about advanced applications of the LM3900 Norton Opamp. I have been developing electronic music circuits in analog and digital form for more than 30 years. In my teens in the 1970s, my very first music synthesizer prototype was based on the LM3900. My reference encyclopedia was AN-72, released by National Semiconductor in September 1972. Over the longer development, time and time again I would return to this very different current differencing amplifier, the LM3900. In this blog, I will share new circuits and applications, along with hopefully what are novel design ideas beyond AN-72.
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ReplyDeleteHi, I'm delighted to discover this research you did on a favorite device of mine, a favorite since I first learned about it when it came out in 1972. You're right, the device's characteristics make possible a number of non-linear functions not covered in AN-72, among which full wave rectification using a single diode between post-neg inputs, and, thanks to the excellent matching of the four amps, its use as an anti-log generator. One of the designs I'm especially proud of, was the design of a complete and accurate exponential VCO with sine to saw voltage controlled waveshape using a single LM3900n costing 75 cents in 1973 :) A copy of the VCO's schematic can be found on Google Images when searching under "Old Serge VCO". Best regards. Serge T.
ReplyDeleteIt’s a real honor to hear from you Serge! Thank-you for the kind words!
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ReplyDeleteJuan,
DeleteThe LM3900 is still widely available, today:
https://www.digikey.com/products/en/integrated-circuits-ics/linear-amplifiers-instrumentation-op-amps-buffer-amps/687?k=LM3900
Kindly
M