Step 7 — Ring-Hot Buffer

WIRING SIDE (back of control plate)
Compound 2N5457 → 2N3904 follower · half-rail bias
Buffer IN ← signal node · RING = buffered + phantom · TIP stays passive
CONTROL PLATE — WIRING SIDE (back view) · this step wires the three buffer pads: IN / GND / RING SIGNAL NODE Volume Lug 2 (wiper) feeds tip · buffer · Q GROUND BUS — all pot casings TRS JACK Switchcraft 12B TIP passive RING SLV passive direct (Step 6) NOT via buffer SLEEVE → GND bus RING-HOT BUFFER SUB-BOARD compound 2N5457 → 2N3904 follower · half-rail divider bias · ~24 × 9 stripboard +V RAIL ≈18 V studio / ≈5.4 V jam (9 V injector) — harvested from the RING GND rail (= GND pad net) Cin 100nF gate Rb1 3M mid (½ rail) Rb2 3M Cmid 1µF Rgm 6M J1 2N5457 D G S nodeA 10.1 V Rs1 22k Q1 2N3904 C B E nodeE 9.4 V Re 3.9k + Couth 100µF 35V Rbo 100Ω Rh 2.2k + Csm 47µF Dz 18V clamp IN GND RING 7.1 — SIGNAL IN Vol Lug 2 → Buffer IN 7.2 — RING pad → Jack RING buffered out + phantom in (one conductor) 7.3 — GND → bus RING-HOT OUTPUT TIP = passive direct, ALWAYS (plain TS = stock bass). RING = buffered out + phantom power in, same wire. SLEEVE = ground. The buffer never touches the tip — the cable picks the path. THD 0.40% @ 1.5 Vpk · Z-balance 0.6% · passive shift −0.27 dB. HALF-RAIL BIAS Rb1 / Rb2 3M divider → mid filtered by Cmid 1µF → gate via Rgm 6M (Zin ≈ 6M, light pickup load). Gate at ½ rail → nodeE ≈ 9.4 V: clean swing. Rs1 22k swamps the 2N5457 Idss spread — no trimming. Couth 100µF (+ to ring) + Rbo 100Ω = output network. POWER — HARVESTED FROM THE RING Phantom DC rides IN on the ring → Rh 2.2k → +V rail. Csm 47µF decouples the rail; Dz 18V zener clamps it. Rail ≈18 V studio (48V phantom) / ≈5.4 V jam (9 V injector). No battery in the bass. Bias scales with the rail; off = 0 V. TS cable grounds the ring → buffer dead, tip still passive. CHECK: IN pad → gate (via Cin)  •  RING pad → Jack RING  •  GND pad → bus  •  NO continuity buffer ↔ TIP (tip stays passive)
Signal in (signal node → IN)
Buffered ring (+ phantom power)
Ground
+V rail (internal, from ring)
Ground bus (context)
TRS jack & signal node (context)

Step 7 Instructions

  1. 7.0 — Build the board first. Populate the ring-hot v2.1 sub-board per the build guide: compound 2N5457 → 2N3904 follower; half-rail divider (Rb1/Rb2 3M, Cmid 1µF, Rgm 6M); Rs1 22k source, Re 3.9k emitter; output network Couth 100µF/35V (+ toward the ring) + Rbo 100Ω; power harvest Rh 2.2k (ring → rail), Csm 47µF, Dz 18V zener. Bench-verify CHECK A/B before wiring it in.
  2. 7.1 — Wire SIGNAL IN. Solder a wire from the signal node (Volume Lug 2 / wiper) to the buffer IN pad. The buffer sits in parallel with the always-live passive tip and draws negligible current.
  3. 7.2 — Wire the RING. Solder a wire from the buffer RING pad to the TRS jack RING terminal. This single conductor carries phantom DC down into the board and the buffered audio up to the output (condenser-mic principle).
  4. 7.3 — Wire GROUND. Solder a wire from the buffer GND pad to the ground bus.
  5. 7.4 — Leave the TIP passive. Do not connect the buffer to the tip. The tip is the passive direct output (wired in Step 6) and stays live regardless of power — a plain TS cable gives you the stock passive bass.
  6. 7.5 — Mount and secure. Fix the sub-board to the cavity with foam tape. Keep leads tidy and clear of the pickup cavities.
No battery. Power arrives as phantom on the ring (18 V studio / 9 V jam injector), harvested through Rh into the +V rail. Continuity checks: IN pad → JFET gate (through Cin); RING pad → Jack RING; GND pad → ground bus. There must be no continuity between the buffer and the TIP, and none between RING and TIP — the two conductors are independent and the cable chooses the path.