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Circuit Atlas · HUSH M4 · Rev 2027.4 draft

S4 Channel filter

Schematic for S4 Channel filter. Design targets and calculations, no measurements.

IN DEVELOPMENT · REV 2027.4 (DRAFT) · DESIGN TARGETS, NOT MEASUREMENTS

HUSH M4 is in development. This draft is published on zakkhutoretsky.com; it has no price and no ordering. Figures marked design target are goals for the finished product. Figures marked calculated come from the published formulas. No value on these pages was measured on a built unit. Interviews are cited as the design brief, not as an endorsement.

See this control Channel filter on the playable panel

S4 Channel filter

Per-channel one-knob split filterA Butterworth Sallen-Key low-pass tuned by a dual-gang log pot and a Butterworth Sallen-Key high-pass tuned by a second dual-gang pot. A window comparator on the knob wiper drives a relay that takes both sections out of the signal path across a dead zone at the centre.S4 CHANNEL FILTER — one-knob split filter, 12 dB per octave, relay true bypassLow-pass, CCW of centre: 18.108k down to 67 HzHigh-pass, CW of centre: 63 up to 5.961k HzINR11.87k + P5aR21.87k + P5bC24.7 nFC14.7 nF−+OAK=1.59Rf5.9kRg10kLP OUTINC110 nFC210 nFR22.67k + P6bR12.67k + P6a−+OAK=1.59Rf5.9kRg10kHP OUTCentre dead zone: true bypassWindow comparatorwiper in dead zone?Relay K1DPDT, audio contactsdriveK1 energised in the dead zone: IN goes straight to OUT.Neither Sallen-Key section is in the signal path.At the dead-zone edge both sections are at their open ends:LP 18.108k Hz, HP 63 Hz.Relay click on the real circuit: a prototype item.One knob, one centre dead zone. CCW of the dead zone: P5 (500k log dual-gang) sweeps the low-pass. CW: P6 (250k logdual-gang) sweeps the high-pass. fc = 1/(2πRC) and Q = 0.71 (Butterworth, low resonance, no peak).The knob also drives the comparator through a third wiper track. The browser model on /mixer uses its own frequencyrange and a smoothed software bypass; it is not this circuit.
S4 Channel filter (schematic) Swipe sideways to pan on a phone.
ItemValue / formula
SectionsButterworth Sallen-Key (12 dB/oct), one low-pass and one high-pass, Q = 0.71R3
Low-passC = 4.7 nF, R = 1.87k + P5 500k dual-gang log: 18,108 Hz down to 67 Hz
High-passC = 10 nF, R = 2.67k + P6 250k dual-gang log: 63 Hz up to 5,961 Hz
ControlOne knob: low-pass counter-clockwise, high-pass clockwise, with a centre dead zone
True bypassA window comparator on a third wiper track drives relay K1 across the dead zone: IN goes straight to OUT and neither section is in the path. At the dead-zone edge both sections sit at their open ends (LP 18,108 Hz, HP 63 Hz)
ResonanceButterworth, Q = 0.71: low resonance, no peakR3
ClickThe relay switching click and the step at the dead-zone edge on the real circuit are prototype measurement items; nothing is claimed here

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