(Acronym for "operational transconductance amplifier") A circuit which is useful for several purposes in an analog synthesizer, it is similar to an operational amplifier, but it has an additional input which allows the gain to be set by an external signal. Basically, this is the description of a voltage controlled amplifier, and in fact it is fairly simple to build a VCA circuit using an OTA. Additionally, the OTA has the useful property of acting like a voltage-controlled resistor. Among other things, this turns out to be handy in designing a certain type of voltage controlled filter. Most of the classic Roland analog synths used an OTA-based VCF design.

Since about 2002, many of the widely used OTA integrated circuits have gone out of production. Analog synth circuit designers are becoming concerned about future availability of OTA ICs. The circuit can be built from discrete components, but doing so takes far more space and requires a certain amount of care in part selection and construction.

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