Circuit Atlas · HUSH M4 · Rev 2027.4 draft
6 Specification (design targets)
Goals and calculations, not measurements of a built unit.
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 Specification on the mixer page Numbers on the mixer page
6 Specification (design targets)
These are goals, not measurements. The third column says whether a figure is a design target or a calculation from the formulas in section 5.
| Item | Value | Basis |
|---|---|---|
| Channels | 4, each phono / line switchable | design target |
| Trim range (line) | -14.9 dB to +14.3 dB | calculated (G = −Rf/Rin) |
| Phono gain at 1 kHz | 38.1 dB (5 mV MM → about 0.4 V) | calculated |
| Phono RIAA accuracy | ±0.2 dB (20 Hz to 20 kHz) | design target |
| Phono RIAA error, nominal values, ideal op-amps | ±0.017 dB | calculated, not a measurement |
| Phono input | 47 kΩ with switchable loading (capacitance values set at prototype) | design target |
| Channel EQ | 4-band (S13): HI shelf 3 kHz +6 dB to kill; HI MID bell 1.1 kHz +10 / −27 dB; LO MID bell 350 Hz +10 / −27 dB; LO shelf 180 Hz +6 dB to kill; exactly flat at 12:00. Shelf split R = 88.7k (179.4 Hz) and 5.36k (2969 Hz) | design target; split frequencies calculated |
| Master isolator | 3-band, LR4 crossovers at 300 Hz and 3 kHz (actual 296.9 Hz and 2969 Hz); full kill to +6 dB | calculated / design target |
| Channel filter | Bipolar HPF / LPF, 12 dB/oct; LPF 18,108 Hz to 67 Hz, HPF 63 Hz to 5,961 Hz; true bypass at centre | calculated |
| Channel fader | 60 mm conductive plastic, control-voltage VCA, 100 dB range; no crossfader | design target |
| Master | 3-band master isolator, master and booth level, mono switch, VU meters L / R | design target |
| Maximum output (balanced) | +28 dBu; rail-limited about +29.6 dBu on ±18 V (1.6 dB margin) | design target / calculated |
| Output impedance (balanced) | 95 Ω | calculated |
| Frequency response | 10 Hz to 40 kHz, ±0.25 dB (line in to master out) | design target |
| THD+N | below 0.003 % at +4 dBu, 1 kHz | design target |
| Signal-to-noise | above 105 dB A-weighted, line in to master out | design target |
| Crosstalk | below −95 dB at 1 kHz between channels | design target |
| Headphones | 6.35 mm and 3.5 mm; 250 mW into 32 Ω (2.83 Vrms) | design target / calculated |
| Power | External linear supply, ±18 V; mains transformer 2 × 22 Vac, 50 VA | design target |
| Effects loop | Switchable send / return, hard-bypassed when off | design target |
| Audio path | Fully analogue, balanced out; no converters in the signal path | design target |
| Outputs | Master XLR, booth XLR, record RCA; transformer-isolated on request | design target |
| USB-C interface (optional) | Record 4 channels plus master and play back; USB Audio Class 2.0; converters on a tap off the analogue path (S10) | design target |
| Texture (optional) | Clean SVF, ladder, comb, bitcrush; resonance, drive, LFO / envelope; analogue ladder / OTA option and DSP card (S11) | design target |
| Spatial FX (optional) | Send / return with a BBD ensemble, digital delay or DSP card option; four browser-model modes: tape echo, spring, plate, BBD ensemble (S12) | design target |
| Left out on purpose | DJ software, screens, menus, crossfader | design target |
Level and rail consistency
The +28 dBu maximum output equals 19.46 Vrms across the balanced pair, or 13.76 V peak per leg. With ±18 V rails and an assumed 16.5 V usable swing per leg, the driver can reach about +29.6 dBu, so 1.6 dB of margin. On ±15 V rails the same driver would top out near +27.8 dBu, which is why the supply is ±18 V and why the swing figure must be confirmed against the chosen op-amp’s datasheet.
Consistency with the /mixer page
- The /mixer specification and this manual both describe op-amp stages: low-noise NE5534 / NE5532-class op-amps for the RIAA stages and an inverting op-amp summer. No discrete or Class A stage is claimed; a discrete input stage is an open item for a later revision.
- Both state no crossfader. The VCA fader stage could host one; it is not fitted in this design.
- The +28 dBu maximum output needs ±18 V rails, as shown above, not the more usual ±15 V.