The Elusive OTA ( Operational Transconductance Amplifier ).  The mythic discontinued current amplifier of the late 60’s early 70’s.   Used in several early synths and guitar pedals of the past and even modern modular filters and pedal kits today!

Operational Transconductance Amplifier 1969

Operational Transconductance Amplifier 1969

Picture by Jpoo

References:

Fascinating OTA story

Muffwiggler

OB filter clone OTA style

STE440 modular Filter

::: IF :::