ALM Busy Circuits Akemie's Castle
Dual 4-operator FM VCO with vintage Yamaha chip
38 HP Eurorack module
Akemie\x27s Castle is a dual voltage controlled oscillator with authentic 4-operator digital FM synthesis using new-old-stock Yamaha YMF262 (OPL3) chips. Each operator features independent waveform selection (8 types), frequency multiplier (1-15x), and level control (0-63), all with voltage control inputs and attenuverters. Six selectable algorithms determine how operators are routed -- from simple 2-operator pairs (one per VCO) to complex 4-operator configurations shared across both oscillators. VCO A features a chord mode producing up to 5-voice chords (16 types including major, minor, diminished, 7ths, 9ths, and detuned) with voltage-controlled chord inversion. Each VCO has independent feedback control for self-modulation. The authentic Yamaha chip provides the distinctive FM sound of 1980s digital synthesis with some inherent character: slight stepping when changing parameters, potential aliasing at extreme settings, and the ability to go from rich tonal beauty to crushing noise. 38HP, +12V: 120mA, -12V: 60mA.
Features
- Dual VCO (Osc A and Osc B) with independent V/Oct, coarse, fine, feedback, and audio output
- Authentic FM synthesis using vintage new-old-stock Yamaha YMF262 (OPL3) chip
- 4 FM operators each with independent waveform selection (8 waveforms), frequency multiplier (1-15), and amplitude level (0-63)
- 6 selectable operator algorithms covering 2-operator and 4-operator serial/parallel combinations
- Full CV control over all operator parameters: wave, multiplier, and level per operator
- Osc A chord mode with 16 chord types including dyads, triads, 4-voice, and 5-voice chords
- Voltage-controlled chord inversion on Osc A via dedicated Inv CV input
- Independent feedback control per VCO (0-7 range); Osc B normalised to Osc A feedback
- All CV inputs expect 0-5V except V/Oct and Chord which expect 0-10V
- White knobs provide offset with attenuator/attenuverter for associated CV inputs
- Grey knobs act as offset with no CV; become attenuators when CV is patched
- Full frequency output range approximately 0.05Hz to just over 6kHz
Controls & Jacks (52)
- Op 1 Wave In — {"basic_tip": "Voltage-control Op 1 waveform.", "description": "CV input for Operator 1 waveform selection."}
- Osc B V/Oct In — {"basic_tip": "Pitch CV input for Osc B.", "description": "1V/Oct pitch input for Oscillator B. Independent pitch tracking from Osc A."}
- Osc A V/Oct In — {"tips": ["Calibrate using rear trimmers: apply 1V and tune to C1, then apply 3V and adjust trimmer until C3"], "basic_tip": "Patch sequence
- Op 2 Wave In — {"basic_tip": "Voltage-control Op 2 waveform.", "description": "CV input for Operator 2 waveform."}
- Op 3 Wave In — {"basic_tip": "Voltage-control Op 3 waveform.", "description": "CV input for Operator 3 waveform."}
- Op 4 Wave In — {"basic_tip": "Voltage-control Op 4 waveform.", "description": "CV input for Operator 4 waveform."}
- Osc A Freq — {"tips": ["For calibration: set Fine and Coarse so 5V on V/Oct produces 1024 Hz", "Acts as an offset to the V/Oct input — does not override
- Osc B Freq — {"related": ["Osc B Fine Tune", "Osc B V/Oct In"], "basic_tip": "Main pitch knob for Osc B.", "description": "Coarse frequency control for O
- Osc A Fine Tune — {"related": ["Osc A Freq"], "basic_tip": "Use for precise tuning against other oscillators or a reference pitch.", "description": "Fine tuni
- Op 1 Multiplier — {"tips": ["The grey knob acts as offset with no CV; with CV patched it becomes an attenuator"], "range": {"max": "15x", "min": "1x (fundamen
- Op 2 Multiplier — {"basic_tip": "Harmonic ratio for Op 2.", "description": "Frequency multiplier for Operator 2 (1-15x)."}
- Op 3 Multiplier — {"basic_tip": "Harmonic ratio for Op 3.", "description": "Frequency multiplier for Operator 3 (1-15x)."}
- Op 4 Multiplier — {"basic_tip": "Harmonic ratio for Op 4.", "description": "Frequency multiplier for Operator 4 (1-15x)."}
- Osc B Fine Tune — {"basic_tip": "Precise pitch adjustment for Osc B.", "description": "Fine tuning control for Oscillator B."}
- Fb CV In — {"basic_tip": "Modulate feedback amount.", "description": "CV input for Osc A feedback (0-5V)."}
- Op 1 Level — {"tips": ["Sweeping level may produce low audible clicks in the last 25% — normal for the YMF262 chip", "Very low levels may not fully mute
- Feedback — {"tips": ["Can affect tuning at higher settings — retune after changing", "Effect varies by algorithm — experiment"], "basic_tip": "0=clean,
- Op 3 Level — {"basic_tip": "Operator 3 strength.", "description": "Amplitude level for Operator 3 (0-63)."}
- Op 4 Level — {"basic_tip": "Operator 4 strength.", "description": "Amplitude level for Operator 4 (0-63)."}
- Op 2 Level — {"basic_tip": "Operator 2 strength.", "description": "Amplitude level for Operator 2 (0-63)."}
- Algorithm LED 1 — {"basic_tip": "Algorithm display.", "description": "LED indicating current algorithm selection."}
- Algorithm LED 2 — {"basic_tip": "Algorithm display.", "description": "Second algorithm indicator LED."}
- Algorithm LED 3 — {"basic_tip": "Algorithm display.", "description": "Third algorithm indicator LED."}
- Op 2 Level Attenuverter — {"basic_tip": "CV depth for Op 2 level.", "description": "Attenuverter for Op 2 Level CV."}
- Op 3 Level Attenuverter — {"basic_tip": "CV depth for Op 3 level.", "description": "Attenuverter for Op 3 Level CV."}
- Chord — {"tips": ["Chords increase output level dramatically — lower operator levels to prevent clipping", "Detuned modes create thick unison sounds
- Op 4 Level Attenuverter — {"basic_tip": "CV depth for Op 4 level.", "description": "Attenuverter for Op 4 Level CV."}
- Op 1 Level Attenuverter — {"basic_tip": "CV modulation depth for Op 1 level.", "description": "Attenuverter for Op 1 Level CV. Sets depth and polarity of voltage cont
- Operator Algorithm — {"tips": ["Algorithms 1-2: independent 2-op per VCO (simplest, most controllable)", "Serial connections = operators FM-modulate each other.
- Fb Attenuverter — {"basic_tip": "CV depth for feedback control.", "description": "Attenuverter for Feedback CV input."}
- Op 1 Mult Attenuverter — {"basic_tip": "CV depth for Op 1 ratio.", "description": "Attenuverter for Op 1 Multiplier CV."}
- Op 2 Offset — {"basic_tip": "Choose Op 2 waveform.", "description": "Waveform selection for Operator 2 (8 waveforms)."}
- Op 2 Mult Attenuverter — {"basic_tip": "CV depth for Op 2 ratio.", "description": "Attenuverter for Op 2 Multiplier CV."}
- Chord Attenuverter — {"basic_tip": "CV depth for chord selection.", "description": "Attenuverter for Chord CV input."}
- Op 3 Offset — {"basic_tip": "Choose Op 3 waveform.", "description": "Waveform selection for Operator 3."}
- Op 3 Mult Attenuverter — {"basic_tip": "CV depth for Op 3 ratio.", "description": "Attenuverter for Op 3 Multiplier CV."}
- Op 1 Offset — {"tips": ["CV-controlled waveform morphing creates timbral animation impossible on classic FM synths"], "basic_tip": "Choose Op 1 waveform.
- Op 4 Mult Attenuverter — {"basic_tip": "CV depth for Op 4 ratio.", "description": "Attenuverter for Op 4 Multiplier CV."}
- Op 4 Offset — {"basic_tip": "Choose Op 4 waveform.", "description": "Waveform selection for Operator 4."}
- Op 1 Level CV In — {"basic_tip": "Patch envelope or LFO for dynamic operator 1 level.", "description": "CV input for Operator 1 level (0-5V expected)."}
- Op 2 Level CV In — {"basic_tip": "Modulate Op 2 level.", "description": "CV input for Operator 2 level."}
- Op 2 Mult CV In — {"basic_tip": "Modulate Op 2 ratio.", "description": "CV input for Operator 2 multiplier."}
- Op 3 Mult CV In — {"basic_tip": "Modulate Op 3 ratio.", "description": "CV input for Operator 3 multiplier."}
- Op 4 Level CV In — {"basic_tip": "Modulate Op 4 level.", "description": "CV input for Operator 4 level."}
- Op 4 Mult CV In — {"basic_tip": "Modulate Op 4 ratio.", "description": "CV input for Operator 4 multiplier."}
- Op 1 Mult CV In — {"basic_tip": "Modulate Op 1 ratio with CV.", "description": "CV input for Operator 1 frequency multiplier."}
- Op 3 Level CV In — {"basic_tip": "Modulate Op 3 level.", "description": "CV input for Operator 3 level."}
- A Out — {"tips": ["Beware distortion when chords are enabled with high operator levels"], "basic_tip": "Main Osc A output. Monitor levels — output c
- Fb CV In 2 — {"tips": ["With nothing patched, Osc B uses the same feedback as Osc A"], "basic_tip": "Patch here for independent Osc B feedback separate f
- B Out — {"basic_tip": "Osc B output. In 4-op modes, same sound as Osc A but at Osc B pitch.", "description": "Audio output for Oscillator B. In 2-op
- Chord CV In — {"basic_tip": "Voltage-control chord type for evolving harmonies.", "description": "CV input for chord type (0-10V expected)."}
- Inv In — {"tips": ["One of the most musical modulation targets — slow LFO creates beautiful harmonic motion"], "basic_tip": "Patch slow LFO for anima
How-To Guides
- Simple Sine Wave Output
- Classic FM Bell Tone
- Punchy FM Bass
- Melodic Chord Inversion Sequence
- FM Percussion and Drum Hits
- Dual VCO FM Drone
- CV-Swept FM Timbre Modulation
- Operator Waveform Morphing
- FM Noise and Texture Exploration
- 5-Voice FM Chord Pad
Explore the interactive Akemie's Castle panel on BleepDex — tap any control to learn what it does.
