Book

Circuit Atlas · HUSH M4 · Rev 2027.4 draft

S12 Spatial FX send / return (optional)

Schematic for S12 Spatial FX send / return (optional). 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 Spatial FX on the playable panel

S12 Spatial FX send / return (optional)

Spatial FX send and returnFour post-fader sends sum in an inverting stage to the FX send bus. Three engine options are drawn: a BBD with clock for ensemble, a PT2399 digital delay for echo, and a DSP card for spring and plate. A return level pot and a hard-bypass switch feed the master mix bus.S12 SPATIAL FX SEND / RETURN — optional; DESIGN TARGET, not built, not measuredSend bus: four post-fader tapsCH1 post-faderRs110kCH2 post-faderRs210kCH3 post-faderRs310kCH4 post-faderRs410kINV SUMU12, -Rf/Rin = -1SEND LEVELpot P10 10k logFX engine: one of three optionsA BBD ENSEMBLE / CHORUSinput LPF - BBD - clock - output LPFMN3207, 1024 stages: delay 2.56 to 51.2 ms (R22)B DIGITAL DELAY (ECHO)input LPF - PT2399 - output LPF, feedback potPT2399: 44 kbit RAM, delay set by a resistor (R21)No delay range is claimed here.C DSP CARD (SPRING, PLATE)ADC - DSP - DAC, or a dedicated reverb ICNo part chosen. Plate topology: Dattorro (R20)ReturnFROM ENGINERETURN LEVELpot P11 10k logfully down = no returnSW3 FX in / bypassRr10kTO MASTER MIX BUS (S7)How the browser model maps to this:Per-channel send, post-fader and post-pan, summed to a stereo bus; the return joins the mix bus before the limiter.Return at 0 adds exact zeros in the model. In hardware SW3 removes the engine from the circuit.The model runs four modes in floating point: tape echo, spring, plate (Dattorro) and BBD ensemble.Hardware options A and B cover only chorus / ensemble and echo. Spring and plate need option C.The model is not the analogue design.BBD parts run from +5 V (R22: +4 to +10 V) and the mixer from +/-18 V: a regulator and level interface are needed.Typical datasheet figures, each maker's own conditions: MN3207 THD 0.4 %, S/N 73 dB; PT2399 THD 0.5 %, SNR > 90 dB.Complete circuits are not drawn.
S12 Spatial FX send / return (optional) (schematic) Swipe sideways to pan on a phone.
ItemValue / formula
StatusDesign target. Nothing here is built or measured. The browser model on /mixer runs the same four modes in floating point so the idea can be heard; it is not the analogue design
TopologyFour post-fader taps through 10k resistors into an inverting sum (gain −Rf/Rin = −1), a send level pot, the FX engine, a return level pot and a hard-bypass switch SW3 into the master sum of S7. With SW3 out the engine is out of circuit, as for S6
Option A, BBD ensembleMN3207, 1024 stagesR22: delay td = 1024 / (2 × fclock); the datasheet gives 2.56 ms at 200 kHz to 51.2 ms at 10 kHz and a +4 to +10 V supply. A 6.4 ms voice needs 1024 / (2 × 0.0064) = 80 kHz (calculated). Typical THD 0.4 % and S/N 73 dB under the datasheet’s own test conditionsR22. Three voices with clocks 120 degrees apart give the ensemble; a clock generator and anti-alias / reconstruction filters are needed and are not drawn. Companding is a design choice for noise, with no part chosen
Option B, digital delayPT2399R21: 44 kbit RAM, delay set by the VCO frequency through one external resistor (10 kΩ recommended, up to 50 kΩ allowed in the datasheet note), THD 0.5 % and SNR better than 90 dB typical, +5 V. Echo feedback would be an op-amp mix of the output back to the input with a pot; wow and flutter from modulating the VCO resistor current is a circuit idea of the designer, not a datasheet claim, and is untested. The datasheet’s delay-time table is on a page not included in the copy read, so no delay range is claimed
Option C, spring and plateReal springs and plates are not modelled by a short BBD. A DSP card (ADC, DSP, DAC) or a dedicated reverb IC would be needed; none is chosen. The plate algorithm in the browser model follows DattorroR20: input diffusers 142, 107, 379, 277 samples, tanks 672 + excursion / 4453 / 1800 / 3720 and 908 + excursion / 4217 / 2656 / 3163 samples at 29,761 Hz, decay-diffusion 0.70 and 0.50, 0.6 output taps from the paper’s Table 2. The spring is the designer’s own: 30 first-order all-pass stages per line for dispersion plus a delay and damping loop; it is not taken from a source
Controls (model)Per-channel send; time / size, feedback / decay, tone, return; mode; tap tempo or tempo sync for the echo. Feedback is capped inside the model: echo 0.85, spring 0.95, plate decay 0.93, BBD regeneration 0.5. Return at 0 adds exact zeros
Browser model limitsNo hiss, clock noise or aliasing of a real BBD is modelled; tape echo has no head or tape model beyond a saturating soft clip and low-pass filters. CPU: measured in Node on the test runner only (see tests/dsp_test.js); no phone was measured

The mixerTechnical manualManual (PDF, 685 KB)Glossary

For music supervisors: sync licensing for film, TV and ads →