Circuit Atlas · HUSH M4 · Rev 2027.4 draft
S1 RIAA phono preamp (moving magnet)
Schematic for S1 RIAA phono preamp (moving magnet). 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
S1 RIAA phono preamp (moving magnet)
| Item | Value / formula |
|---|---|
| Standard | Playback curve with time constants 3180, 318 and 75 µsR1, R2 |
| U1 | Non-inverting, G = 1 + Rf1/Rg1 = 1 + 2.21k/220 = 11 (+20.9 dB); Cg1 = 470 µF puts the stage high-pass corner at 1/(2π·220·470 µF) = 1.5 Hz |
| U2 | Shelf: pole at Rf2·Cf2 = 20k × 160 nF = 3.2 ms (3180 µs), zero at Rf2·Cf2/(1 + Rf2/Rg2) = 318 µs. Rf2/Rg2 = 20k/2.21k ≈ 9 |
| R3·C3 | Passive low-pass, 5.76k × 13 nF = 74.9 µs (75 µs) |
| U3 | Flat gain 1 + 6.19k/1k = 7.19 (+17.1 dB): total at 1 kHz = 38.1 dB, a design target of 38 dB for a 5 mV moving-magnet cartridge |
| Noise | U1 should be the lowest-noise op-amp in the design (NE5534-class, 3.5 nV/√Hz typ)R7, R6; the 220 Ω gain resistor contributes about 1.9 nV/√Hz (√(4kTR)) |
| Result | Calculated RIAA error with these E96/E24 values and ideal op-amps: ±0.017 dB, 20 Hz to 20 kHz. A real build adds op-amp bandwidth error, part tolerance and cartridge loading; the 20 Hz IEC rumble corner is not included |