Circuit Atlas · HUSH M4 · Rev 2027.4 draft
S13 Channel EQ (four-band, per channel)
Schematic for S13 Channel EQ (four-band, per channel). 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 Four-band channel EQ on the playable panel
S13 Channel EQ (four-band, per channel)
| Item | Value / formula |
|---|---|
| Status | Design target. Nothing here is built or measured. The browser model on /mixer is floating-point DSP that follows the same control law; it is not a simulation of this circuit |
| Bands | HI shelf 3 kHz: +6 dB to full kill. HI MID bell 1.1 kHz: +10 dB to −27 dB. LO MID bell 350 Hz: +10 dB to −27 dB. LO shelf 180 Hz: +6 dB to full kill. Every knob is exactly 0 dB at 12:00 (centre detent). Where these figures come from is stated in the manual, section 5, S13 |
| Strip order | Trim, LO MID bell, HI MID bell, three-way LR4 split with LO and HI band pots, then the filter (S4) and the fader (S5). The cue tap stays pre-fader |
| Bells (two stages) | Each bell is an inverting op-amp stage with a 10k linear pot and a band-pass filter tuned to the bell frequency, the virtual-earth boost / cut arrangement described by ESPR23. ESP lists multiple-feedback, twin-T and state-variable band-passes as options; this design picks multiple-feedback for part count (a design choice). At the pot centre the band-pass has no effect and the stage is a unity inverter, so it is flat. Two inverting stages in series keep absolute polarity. Bell Q about 0.9 at full boost (design choice). Component values are not calculated in this draft |
| Shelves (kill) | A plain Baxandall shelf cannot reach full kill, so LO and HI reuse the S3a LR4 split insteadR3, R4: crossovers at 180 Hz (R = 88.7k, f0 = 179.4 Hz) and 3 kHz (R = 5.36k, f0 = 2969 Hz) with C = 10 nF. LO and HI bands each get a ×2 band amp and a 10k linear pot (minimum = kill, centre = unity, maximum = +6 dB); the middle leg gets ×2 then a fixed divide-by-2; an inverting sum recombines |
| Kill depth | Design target: beyond 60 dB in the stop band of the LR4 split, as for S3b. Not measured |
| Model versus circuit | The browser model uses second-order shelf and peaking sections (the textbook biquad forms, not cited to a page in this draft) with the same corner and centre frequencies and the same plateau levels, and a −80 dB floor for kill. The LR4 split has steeper transitions near 180 Hz and 3 kHz, so the two differ in the transition regions |
| Headroom | Boosts stack: with every band up the strip can add well over 10 dB at some frequencies. Headroom for that has not been analysed in this draft. The model on /mixer keeps its limiter on the master output only |
| Op-amp sections | Bells: 2 sections each, 4 per channel. Split: 12 sections per channel (see the budget in S9) |