There were a couple requests to retrofit a LM13700 into a noise gate/ expander board that originally called for a CA3080.
This is one of the projects that appeared in a Japanese effects book from the 80s. These files have been available on Mark Hammer's site (Ampage) as well as a few other places on the net.
I kept the board layout close to the original, but added a few things. Among the things that were added were input/output pull down resistors, a resistor tied to V+ and pad for effect engaged LED, and a few extra ground pads. Also, the original 2SC1222 and 2SA640 transistors were changed to BC550 and BC560.
There were a few discrepancies between the original schematic and original board routing/layout. These were mainly component positions switched. (C10<>R14, C8<>R12, C6<>R8) The redrawn schematic reflects the original board layout.
As noted above, there is a pad for an effect engaged LED. This would be the pad in the upper right corner marked "LED".
There is an additional LED marked "D5". This should be a gating indicator, and should turn on and off with the gating.
It is my thought that some experimenting can be done with this circuit. The Expand/Normal switch (SW1) can possibly be changed to a 50K pot. (with an additional resistor to ground?)
TR2 can be changed to a 5 or 10K pot? Level control?
Just some things I'm throwing out for the mod minded.
Here's the project file PDF:https://dl.dropboxusercontent.com/u/53299166/DIYstompboxes/Noisegate-Expander%20file.pdf