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Circuit Atlas · HUSH M4 · Rev 2027.4 draft

S2 Line input and trim

Schematic for S2 Line input and trim. 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 Front panel key Channel 1 controls

S2 Line input and trim

Line input and trim, one channelInput coupling, RF filter, an inverting trim stage with a rheostat for plus and minus 15 dB, and a unity inverter that restores polarity.S2 LINE INPUT AND TRIM — one of four identical channelsLINE IN+Ci2.2 µFRb47kRrf1kCrf220 pFRin10k−+U4G = −Rf/RinRt1.8kP1 50k trimRin210k−+U5unity inverterRf210kTO INPUT SELECTTrim range -14.9 dB to +14.3 dB (formula G = −Rf/Rin, Rf = 1.8k to 51.8k, Rin = 10k). RF filter corner 723,432 Hz(1/2πRC), input high-pass 1.5 Hz.
S2 Line input and trim (schematic) Swipe sideways to pan on a phone.
ItemValue / formula
TrimInverting stage, G = −Rf/Rin, Rin = 10k, Rf = 1.8k (fixed) + P1 50k: -14.9 dB to +14.3 dB
PolarityU5 is a unity inverter so the line path has the same absolute polarity as the phono path
FiltersRF low-pass 1/(2π·1k·220 pF) = 723 kHz; input coupling 2.2 µF into 47k = 1.5 Hz high-pass

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