Single-ended by choice
Pin 2 goes straight into C1. The balanced receiver lives on sheet 4 — this sheet is deliberately the shortest path from jack to amplifier.
Note 01
Revision history
Every trace on this sheet has been walked twice — once by the router and once by hand. Northwire publishes its schematics because a preamp you cannot read is a preamp you cannot repair in twenty years.
| Rev | Date | Change | By |
|---|---|---|---|
| C.4 | 2026-07-19 | D1 changed to BAT54; clamp now soft-knees 400 mV before the rail. | M. Ferrow |
| C.3 | 2026-05-02 | R4 build-out raised 47R → 100R for cable capacitance stability. | M. Ferrow |
| C.1 | 2026-02-11 | C3 relocated within 4 mm of U1 pin 8. Star ground moved to J2 shell. | A. Öberg |
| B.7 | 2025-11-30 | Gain network rescaled: R2/R3 = 100k/2k2, +34 dB nominal. | A. Öberg |
| B.0 | 2025-08-14 | First silicon-verified sheet. Op-amp fixed at OPA1642. | M. Ferrow |
One rail, one return
AGND is a single horizontal net. Junction dots are the only bonds; anything crossing without a dot is a hop, drawn deliberately un-fudged.
Indicator on the rail
R6 and D2 hang off +15V so the module tells you it is alive before you plug anything into it. 1.4 mA — quiet enough to leave in the audio path's neighbourhood.