M6 c2

docs/CIRCUIT.md

@@ -22,6 +22,7 @@ V1a part:
 | V1a | 12AX7 | p1a, g1a, k1a | |
 | R1 | 2.7 kΩ | k1a – gnd | |
 | C1 | 0.68 µF | k1a – gnd | Full cathode bypass |
+| C2 | 100 pF | p1a – k1a | V1a plate–cathode (drawing iss. 4; added D-062, was open item O8) |
 | R4 | 100 kΩ | bpA – p1a | Plate load; bpA from supply B7 |
 
 There is no junction between V1a and V1b: p1a is an internal node of B12 (the J1 junction was
@@ -253,7 +254,7 @@ Regenerate with `python3 reference/spice/spice_tools.py` after any netlist chang
 | O5 | NFB tap | 16 Ω output with the speaker load (D-059) | Feedback amount if taken from another tap |
 | O6 | Low input | Not modelled | Feature only |
 | O7 | OT half-primary orientation | Blue–White (15.36 Ω) on the pA side (V4/V5) | ±0.6 Ω winding asymmetry, about ±40 mV DC per side |
-| O8 | C2 100 pF V1a plate–cathode (drawing 2203 STD Preamp iss. 4) | Not in the netlist (found 2026-10-15) | −0.3 dB at 5 kHz, −0.7 … −0.9 dB at 10 kHz into V1b (SPICE study) |
+| O8 | C2 100 pF V1a plate–cathode | Resolved: in the netlist since D-062 | −0.3 dB at 5 kHz, −0.7 … −0.9 dB at 10 kHz into V1b (SPICE study) |
 | A1 | HT source 505 V / 100 Ω | Assumed | B+ level and sag |
 | A2 | OT values | Hammond 1750U replacement datasheet, primary inductance fitted (§3, D-023) | Power, LF/HF response, feedback |
 | A3 | Choke 5 H / 115 Ω | Hammond 194F replacement datasheet; L specified at 120 mA DC, the amp runs it at ≈ 27 mA (D-024) | Screen node dynamics, supply DC |

docs/DECISIONS.md

@@ -1043,3 +1043,14 @@ at 0 V. Above +20 V, P = Vpk within 0.1 V (DC operating point unchanged).
 Consequences: engine diagnostic: HOT DI 0 power-amp failures at 8x and 16x; CRUNCH / DRIVE unchanged (−218 … −224 dB vs
 the previous engine), HOT differs by −35 … −37 dB. tests/data EL34 sweeps regenerated; the pentode test asserts the new
 below-cathode behaviour. SPICE references with the power amp are re-rendered.
+
+## D-062 C2 100 pF (V1a plate–cathode) added to the netlist (reference model change)
+Date: 2026-10-18 · Status: accepted (owner: "add C2 to the netlist")
+Context: the drawing (2203 STD Preamp iss. 4) shows C2 100 pF from V1a's plate to its cathode; it was missing from the
+transcription (open item O8, found 2026-10-15). SPICE study: −0.3 dB at 5 kHz, −0.7 … −0.9 dB at 10 kHz into V1b.
+Decision: `C2 p1a k1a 100p` in the netlist (B12 partition). The engine adds it to V1a's plate–cathode capacitance port
+(`cpk1a_` = Cpk + C2 in `Preamp` and `StageV1aV1b`): the same two nodes, so the parallel combination is exact.
+Consequences: DC unchanged. Every SPICE reference containing V1a is re-rendered; earlier reports are without C2.
+Also found: the standalone blocks' default supply voltages (Preamp, StageV1aV1b, StageV2aV2b, StageV2aV2bToneStack,
+PhaseInverter, PowerStage) were still the pre-D-058 values (bpA 389.35, bpX 402.34, ct 488.71, nScr 485.65 V); updated to
+CIRCUIT.md §5 (391.92, 405.00, 491.35, 488.88 V) with the block DC fixtures (the full amp sets its supplies itself).

docs/PROGRESS.md

@@ -842,6 +842,13 @@ Notes:
   model) and are now rendered once more at RELTOL 1e-7 by `render_spice` (as the M3 cascade), noted in the reports. Plugin
   model check: Full 2x HOT −24.2 dB (PASS), unseen −20.8 dB, 94 first-solve failures (2 unrescued) over 28 runs, nearly all in
   the extreme validation settings (presets: 0 / 0 / 2); Half 2x HOT −18.9 dB. Presence knob jump −62.9 dB; null test 26 / 26.
+- Owner 2026-10-18: add C2 to the netlist (D-062). Plan: `C2 p1a k1a 100p`; the engine folds it into V1a's Cpk port (Cpk + C2,
+  B1234 and B12: the same nodes, exact); B12 partition; re-verify b12 (DEFAULT, VOL0.2, VOL1.0), b1234, knob jumps b12 / b1234,
+  M4 acceptance at 768 kHz and 384 kHz exact J4 + HOT, plugin model check (Full 2x), null test, CPU.
+- D-062 done. b12 / b1234 first failed on DC (≈ 0.65 %): the standalone blocks' default supplies were pre-D-058; fixed
+  (engine headers + block DC fixtures). Then: b12 DEFAULT / VOL0.2 / VOL1.0 105 / 106 / 106 PASS, b1234 119 PASS, b3 87 PASS,
+  b34 94 PASS (0 FAIL each); knob jumps b12 −55.9 dB, b1234 −39.1 … −55.1 dB, b34 −53.1 … −67.6 dB; M4 full acceptance 107
+  PASS (768 kHz and 384 kHz exact J4); HOT 20 PASS / 1 FAIL (2 rescued first-solves, as after D-061); null test 26 / 26.
 
 ## Questions for the owner
 _(Claude Code: add questions here and also ask them in the session.)_

engine/include/amp2203/PhaseInverter.h

@@ -26,7 +26,7 @@ namespace amp2203 {
 /// (g3b−k3, p3b−k3). Presence is smoothed (SPEC §6.2); R_th4 follows the preamp's knobs.
 class PhaseInverter {
 public:
-    static constexpr double kSupplyBpX = 402.335999;  // CIRCUIT.md §5
+    static constexpr double kSupplyBpX = 404.998185;  // CIRCUIT.md §5
     static constexpr int kParamUpdateInterval = 32;
     static constexpr int kNodes = 8, kElements = 18, kRootPorts = 4;
 

engine/include/amp2203/PowerStage.h

@@ -25,7 +25,7 @@ namespace amp2203 {
 /// resistances as one coupled element, the load); root ports (g, s, p) of each pair against ground.
 class PowerStage {
 public:
-    static constexpr double kSupplyCt = 488.708422, kSupplyScreen = 485.649287;  // CIRCUIT.md §5
+    static constexpr double kSupplyCt = 491.346637, kSupplyScreen = 488.880467;  // CIRCUIT.md §5
     /// J5 Thevenin resistances (harness/junctions.py j5a / j5b, provisional; CIRCUIT.md §4).
     static constexpr double kRthA = 58067.6, kRthB = 56937.4;
     static constexpr int kNodes = 17, kElements = 31, kRootPorts = 6;

engine/include/amp2203/Preamp.h

@@ -25,14 +25,14 @@ namespace amp2203 {
 /// while one moves, the matrices are recomputed every kParamUpdateInterval samples.
 class Preamp {
 public:
-    static constexpr double kSupplyBpA = 389.349603;  // CIRCUIT.md §5; B7 sets them in M4
-    static constexpr double kSupplyBpX = 402.335999;
+    static constexpr double kSupplyBpA = 391.921506;  // CIRCUIT.md §5 (after D-058); B7 sets them in M4
+    static constexpr double kSupplyBpX = 404.998185;
     static constexpr int kParamUpdateInterval = 128;  // samples between matrix updates while a knob moves (D-057; was 32)
     static constexpr int kNodes = 20, kElements = 38, kRootPorts = 9;  // 8 triode ports + the load at y
 
     // Component values, CIRCUIT.md §1 and tubes.lib (SI units).
     static constexpr double R1 = 2.7e3, R3 = 68e3, R4 = 100e3, R5 = 470e3, R6 = 10e3, R7 = 100e3;
-    static constexpr double C1 = 0.68e-6, C3 = 0.022e-6, C4 = 470e-12, C5 = 1e-9, VR1 = 1e6;
+    static constexpr double C1 = 0.68e-6, C2 = 100e-12, C3 = 0.022e-6, C4 = 470e-12, C5 = 1e-9, VR1 = 1e6;
     static constexpr double R9 = 820.0, R10 = 470e3, R11 = 470e3, R12 = 100e3, R13 = 100e3, R15 = 33e3;
     static constexpr double C7 = 0.022e-6, C8 = 470e-12, C10 = 470e-12, C11 = 0.022e-6, C12 = 0.022e-6;
     static constexpr double VR3 = 220e3, VR4 = 22e3, VR5 = 1e6, VR2 = 1e6;
@@ -114,7 +114,8 @@ class Preamp {
     chowdsp::wdft::ResistorT<double> vr1b_{1.0};
     chowdsp::wdft::ResistorT<double> r6_{R6};
     chowdsp::wdft::ResistiveVoltageSourceT<double> src7_{R7};
-    detail::DcCapacitor cgk1a_{Cgk}, cgp1a_{Cgp}, cpk1a_{Cpk}, cgk1b_{Cgk}, cgp1b_{Cgp}, cpk1b_{Cpk};
+    // cpk1a_: V1a's Cpk in parallel with C2 (100 pF plate–cathode, D-062): one p1a – k1a port
+    detail::DcCapacitor cgk1a_{Cgk}, cgp1a_{Cgp}, cpk1a_{Cpk + C2}, cgk1b_{Cgk}, cgp1b_{Cgp}, cpk1b_{Cpk};
     // B3 elements
     detail::DcCapacitor c7_{C7};
     chowdsp::wdft::ResistorT<double> r10_{R10};

engine/include/amp2203/StageV1aV1b.h

@@ -28,13 +28,13 @@ namespace amp2203 {
 class StageV1aV1b {
 public:
     /// Supply node bpA at the F operating point (CIRCUIT.md §5, as the B12 testbench); B7 sets it in M4.
-    static constexpr double kSupplyBpA = 389.349603;
+    static constexpr double kSupplyBpA = 391.921506;
     static constexpr int kParamUpdateInterval = 32;
     static constexpr int kNodes = 8, kElements = 15, kRootPorts = 4;
 
     // Component values, CIRCUIT.md §1 B12 and tubes.lib (SI units).
     static constexpr double R1 = 2.7e3, R3 = 68e3, R4 = 100e3, R5 = 470e3, R6 = 10e3, R7 = 100e3;
-    static constexpr double C1 = 0.68e-6, C3 = 0.022e-6, C4 = 470e-12, C5 = 1e-9, VR1 = 1e6;
+    static constexpr double C1 = 0.68e-6, C2 = 100e-12, C3 = 0.022e-6, C4 = 470e-12, C5 = 1e-9, VR1 = 1e6;
     static constexpr double Cgk = 2.3e-12, Cgp = 2.4e-12, Cpk = 0.9e-12;
 
     StageV1aV1b();
@@ -90,7 +90,8 @@ class StageV1aV1b {
     chowdsp::wdft::ResistorT<double> vr1b_{1.0};
     chowdsp::wdft::ResistorT<double> r6_{R6};
     chowdsp::wdft::ResistiveVoltageSourceT<double> src7_{R7};
-    detail::DcCapacitor cgk1a_{Cgk}, cgp1a_{Cgp}, cpk1a_{Cpk}, cgk1b_{Cgk}, cgp1b_{Cgp}, cpk1b_{Cpk};
+    // cpk1a_: V1a's Cpk in parallel with C2 (100 pF plate–cathode, D-062): one p1a – k1a port
+    detail::DcCapacitor cgk1a_{Cgk}, cgp1a_{Cgp}, cpk1a_{Cpk + C2}, cgk1b_{Cgk}, cgp1b_{Cgp}, cpk1b_{Cpk};
 
     auto elements() noexcept {
         return std::tie(vin_, k1a_, src4_, c3_, r5c4_, c5vr1a_, vr1b_, r6_, src7_, cgk1a_, cgp1a_, cpk1a_, cgk1b_,

engine/include/amp2203/StageV2aV2b.h

@@ -25,7 +25,7 @@ class StageV2aV2b {
     /// J2 Thevenin resistance (harness/junctions.py j2, |Z(1 kHz)| of B12 at p1b; DECISIONS D-018).
     static constexpr double kRth2 = 89732.8;
     /// Supply node bpX at the F operating point (CIRCUIT.md §5, as the B3 testbench); B7 sets it in M4.
-    static constexpr double kSupplyBpX = 402.335999;
+    static constexpr double kSupplyBpX = 404.998185;
     static constexpr int kNodes = 6, kElements = 13, kRootPorts = 4;
 
     // Component values, CIRCUIT.md §1 B3 and tubes.lib (SI units).

engine/include/amp2203/StageV2aV2bToneStack.h

@@ -26,7 +26,7 @@ namespace amp2203 {
 class StageV2aV2bToneStack {
 public:
     static constexpr double kRth2 = 89732.8;          // harness/junctions.py j2 (D-018)
-    static constexpr double kSupplyBpX = 402.335999;  // CIRCUIT.md §5; B7 sets it in M4
+    static constexpr double kSupplyBpX = 404.998185;  // CIRCUIT.md §5; B7 sets it in M4
     static constexpr int kParamUpdateInterval = 32;
     static constexpr int kNodes = 13, kElements = 24, kRootPorts = 4;