Make: Analog Synthesizers

Appendix B. The LM13700

The LM13700 Dual Transconductance Op Amp is one of the coolest integrated circuits around today for building the components of analog synthesizers. A transconductance op amp is a special type of op amp that can be thought of as a voltage-controlled current source. The LM13700 is one of the few really useful transconductance amplifiers that are still in production.

Several chip houses are manufacturing the LM13700 with different part numbers, but all use the same circuit originally designed by Don Sauer and Bill Gross, of National Semiconductor. Read Don Sauer’s interesting account of the chip’s design and development on his website, The LM13600/LM13700 Story.

The LM13700 is at the heart of many VCFs, VCAs, VCO wave shapers, ...