Bucket Brigade Device (BBD) Analog Stereo Chorus (MN3007 / MN3009)
Analog charge-transfer delay line ICs used to generate the iconic wide stereo chorus in Roland Juno and modern boutique synthesizers.
# Mathematical Formula & Architecture
Logic SpecificationDelay Time t_d = N / (2 * f_clock). Modulating f_clock via an analog LFO generates pitch modulation (vibrato + direct = chorus).
BBD Clocking Flow:
High-frequency 2-phase clock (MN3101) ---> Capacitive charge packets shifted along 1,024 stages (MN3007)
Output: Delayed analog signal mixed with dry input to generate comb-filtered stereo spread.# Deep Technical Analysis & Historical Context
Because early polyphonic synthesizers like the Roland Juno-6, Juno-60, and Juno-106 had only one oscillator (DCO) per voice to reduce cost, chords could sound thin compared to dual-oscillator boards like the Prophet-5. Roland brilliantly solved this by routing the mono mix bus through an onboard stereo analog Bucket Brigade Device (BBD) chorus circuit powered by Matsushita/Panasonic MN3009 or MN3007 ICs. A BBD consists of hundreds of MOS capacitors. Analog voltage samples are shuttled down the capacitor line like a fire brigade passing buckets of water, creating short, warmth-saturated analog delays (5ms to 30ms). When swept by dual anti-phase LFOs and blended with the direct sound, the single-oscillator Juno instantly transforms into a massive, shimmering polyphonic wall of sound.
Common Studio Pitfall & Hardware Hazard
BBD chips inherently produce a faint high-frequency background hiss; engaging Juno Chorus Mode II without an audio gate can introduce noise floor build-up during quiet passages.
# Hardware Synthesizers Using This Technology
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# Frequently Asked Engineering Questions
Why does the Juno chorus sound so much wider than digital plugins?
Real BBD circuits introduce mild non-linear harmonic distortion, subtle compander coloration, and imperfect analog clock filtering that digital algorithms rarely model authentically.
Related Engineering Concepts
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