LM13600/13700 History and links

[expanoncolin]

Last night I stumbled upon this story about how the LM13600/13700 operational transconductance amplifier was created.  Interestingly, it is a pretty blatant rip-off of the 3080 series chip, and was mostly made as an exercise to learn IC design!  I particularly liked this image, which is a hacked together solder prototype of the chip:

The LM13600/13700 has now outlasted the 3080, and is a totally vital chip for synths because of its voltage-controllability.  It also has really nice clipping characteristics.  It's somewhat common in analog synths, but I'm surprised it isn't completely ubiquitous.  The page also has a lot of great links to application examples, including articles and the very helpful datasheet (scroll to the bottom).

-Colin

[marmora]

Awesome post.  Love that picture!

[ve3wwg]

Ya, I saw that recently looking at everything OTA/LM13700.

Another good one is this (recently encountered):

http://101science.com/transistor.htm

(The First Point Contact Transistor)

Warren

[pete.m]

I have 10 3080's and some 13700's waiting for something, preferably guitar signal mangling. Any suggestions?

Also, there's a pretty good OTA theory explanation in Musical Applications of Microprocessors (I think...I'll have to check for sure).

pete.m

[expanoncolin]

Good places to start:

http://www.geofex.com/Article_Folders/VCA%20Applications.pdf

http://img294.imageshack.us/img294/5702/93446124.png

And, tons of musicfromouterspace designs use them.

-Colin

[mikebike]

Multichannel fadeover morpher!