Circuit Atlas · HUSH M4 · Rev 2027.4 draft
A Derivations and component values
The same numbers printed by tools/mixer_values.py.
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 Open the mixer
A Derivations and component values
All values come from tools/mixer_values.py; running it prints the same numbers.
RIAA
Playback curve H(s) = (1 + s·318 µs) / ((1 + s·3180 µs)(1 + s·75 µs))R1, R2. U2 provides the 3180 / 318 µs shelf: for G = 1 + Zf/Rg with Zf = Rf in parallel with Cf, the pole is at Rf·Cf and the zero at Rf·Cf/(1 + Rf/Rg), so Rf·Cf = 3180 µs and Rf/Rg = 9 give a 318 µs zero. A passive R·C = 75 µs follows. A non-inverting stage cannot fall below unity gain, which is why the 75 µs roll-off is passive and the gain is made up in U3.
| Check frequency | Error vs ideal RIAA (dB) |
|---|---|
| 20 | 0.01 |
| 50 | 0.011 |
| 100 | -0.001 |
| 500 | -0.005 |
| 1000 | -0.0 |
| 2122 | 0.006 |
| 5000 | 0.011 |
| 10000 | 0.013 |
| 20000 | 0.013 |
Sallen-Key and Linkwitz-Riley
For equal R and C: f0 = 1/(2πRC), Q = 1/(3 − K), K = 1 + Rf/RgR3. K = 1.586 gives Q = 0.707 (Butterworth); two such sections in cascade make an LR4 filter with the −6 dB point at f0R4. With C = 10 nF: R(300 Hz) = 53.05 kΩ → 53.6k; R(3 kHz) = 5.305 kΩ → 5.36k.
Power
Vout = 1.25 × (1 + R2/R1) with R1 = 240 Ω and R2 = 3.24k gives 18.29 VR5. Reservoir ripple ΔV = I/(f·C) with f = 100 Hz for full-wave rectification.
Levels
0 dBu = 0.7746 Vrms. +28 dBu = 0.7746 × 10^(28/20) = 19.46 Vrms. Balanced peak per leg = Vrms × √2 / 2 = 13.76 V.