Roland IR3109 Quad Operational Transconductance Amplifier (OTA)
Roland's proprietary quad OTA integrated circuit powering the filters of the Jupiter-8, Juno-6, Juno-60, and early MKS-80.
# Mathematical Formula & Architecture
Logic SpecificationGm = I_abc / (2 * V_t). Cutoff frequency f_c is directly proportional to amplifier bias current I_abc.
Roland IR3109 Architecture (16-pin SIP):
Four identical matched OTAs on one die.
Configured as 4-pole cascaded integrator lowpass filter (-24dB/octave slope)
with external buffer transistors and negative feedback resonance loop.# Deep Technical Analysis & Historical Context
Manufactured by Roland in the late 70s and early 80s, the IR3109 is widely considered one of the holy grails of analog synthesizer filter ICs. Unlike general-purpose OTAs like the CA3080 or LM13600 which required multiple external packages to construct a 4-pole filter, the IR3109 integrated four matched transconductance cells onto a single monolithic substrate with integrated temperature-compensation diodes. In the Roland Juno-6 and Juno-60, the IR3109 provides pristine, velvety filtering that does not thin out in the low end as resonance increases, defining the signature lush sound of early 80s synth-pop and synthwave.
Common Studio Pitfall & Hardware Hazard
Counterfeit IR3109 chips sourced from unverified online sellers often contain repacked low-slew dual op-amps that oscillate violently or produce distorted audio.
# Hardware Synthesizers Using This Technology
Click any synthesizer below to explore its specific memory protect routine, factory soundbanks, and Web MIDI SysEx cloud backup engine:
# Frequently Asked Engineering Questions
What is the difference between the Juno-60 and Juno-106 filter?
The Juno-60 uses the standalone IR3109 chip on its mainboard. The Juno-106 shrunk this design into the 80017A hybrid module, combining the IR3109 circuit with dual BA662 VCA clones under resin.
Related Engineering Concepts
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