{
  "format": "circuit-codex-reference",
  "version": 1,
  "id": "aa964",
  "url": "https://circuitcodex.com/amps/aa964/",
  "attribution": "The Analog Maker / Circuit Codex",
  "license": "https://creativecommons.org/licenses/by-sa/4.0/",
  "revision": "ebddc3fd2cf887dca010bbe60487d7391ea6c052",
  "scope": "DC and drawing checks have separate coverage. See included check results and the circuit page; not a dimensioned build template or a physical-build certification.",
  "metadata": {
    "id": "aa964",
    "name_style": "Blackface Princeton-style",
    "family": "blackface",
    "era": {
      "start": 1964,
      "end": 1968
    },
    "wattage": 12,
    "tubes": [
      "12AX7",
      "12AX7",
      "6V6GT",
      "6V6GT",
      "GZ34"
    ],
    "topology": {
      "rectifier": {
        "kind": "tube",
        "type": "GZ34"
      },
      "bias": "fixed",
      "phase_inverter": "cathodyne",
      "tone_stack": "tb"
    },
    "lineage": {
      "derived_from": [
        "6g2"
      ],
      "influenced": []
    },
    "conventions": {
      "designators": "functional"
    },
    "sources": [
      {
        "desc": "Fender 'Princeton-Amp AA964' schematic (drawing 045419): every component value AND the printed voltage chart read directly from the published sheet (+420 V reservoir/OT centre tap and 6V6 plates, +415 V screens, +290 V preamp/inverter rail, +190 V both 7025 plates with +1.5 V cathodes, cathodyne +220 V plate / +65 V cathode / +63.8 V junction, tremolo oscillator +260 V plate and +2.4 V cathode, -34 V fixed bias; dropper chain 1 k-1 W then 18 k-1 W + 18 k-1 W with four 20 uF-450 V cans; cathodyne = 56 k plate load, 1 k cathode resistor to a 56 k tail, 1 M grid leak returned to that junction; 6V6 220 k 5% grid leaks and no screen stoppers; 2.7 k negative feedback from the speaker to the 47 ohm tail under V1B's 1.5 k cathode resistor; TR1 125P1B 340-0-340 V, TR2 125A10B). Notice: values +/-20%, read to ground with an electronic voltmeter, resistors 1/2 W 10% and capacitors 400 V unless marked. The preamp bottle is labelled 7025 (a 12AX7 alias). Not reproduced here; archived at EL34World",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_AA964_schem.pdf"
      },
      {
        "desc": "Fender 'Princeton-Amp AA964' layout drawing (L-FD): the physical order of the board parts, the chassis-mounted multi-section filter can (four 20 uF-450 V sections at +420 / +415 / +370 / +290 V, with one 18 k-1 W dropper mounted at the can), the wire colours (PT red/red-yellow HT, yellow 5 V rectifier filament, green/green-yellow 6.3 V heaters; output transformer brown and blue to the 6V6 plates, red centre tap, green and black to the speaker jacks; blue to the vibrato-pedal jack), and the socket pin numbering read off the sheet. It prints +370 V at the filter node the schematic leaves unlabelled. Not reproduced here; archived at EL34World",
        "url": "https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_AA964_layout.pdf"
      },
      {
        "desc": "Wikipedia, Fender Princeton — the push-pull 6V6 Princeton's commonly cited 12 W rating (the drawing prints no output power)",
        "url": "https://en.wikipedia.org/wiki/Fender_Princeton"
      }
    ],
    "verification": {
      "status": "verified",
      "date": "2026-08-02T00:00:00.000Z",
      "max_deviation_pct": 5.5
    },
    "contributors": [
      "TheAnalogMaker"
    ],
    "sections": {
      "V2A": "excluded — the tremolo's phase-shift oscillator: a running oscillator has no static operating point; its 220k plate load returns to the driven rail BA"
    }
  },
  "parts": {
    "notes": "The schematic draws both instrument jacks (1 and 2) with their normalling contacts; this sheet draws them as the two input labels, with the 1 MΩ leak at jack 1's tip, jack side of its 68 kΩ stopper, where both L-FD pages put it. The tremolo oscillator's parts are listed in full, but its DC operating point is excluded from the simulation for the reason given in the circuit notes below. Tube designators V1–V5 are this archive's, not the drawing's — Fender numbered the sockets on the tube chart, not the schematic; the TR1/TR2 transformer labels are the drawing's own. The 125P1B is the power transformer Fender shared across the Champ, the Princeton and the Princeton Reverb, and the HT winding is not annotated the same way on every sheet: this drawing prints 340-0-340 V, as does the Princeton Reverb AA1164, while the Champ AA764 sheet prints 320-0-320 V for the same part number. Each entry records the figure its own drawing prints.",
    "items": [
      {
        "ref": "R1n",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Input grid stopper (jack 1)"
      },
      {
        "ref": "R2n",
        "part": "Carbon comp resistor",
        "value": "68 kΩ · ½ W",
        "role": "Input grid stopper (jack 2)"
      },
      {
        "ref": "RG1A",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Input leak, jack 1's tip to ground (jack side of R1n); the grid's DC return through R1n"
      },
      {
        "ref": "RL1A",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1A plate load"
      },
      {
        "ref": "RK1A",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V1A cathode bias"
      },
      {
        "ref": "CK1A",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V1A cathode bypass"
      },
      {
        "ref": "CT",
        "part": "Mica capacitor",
        "value": "250 pF",
        "role": "Treble cap, plate to treble pot"
      },
      {
        "ref": "RS",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "Tone-stack slope resistor"
      },
      {
        "ref": "CB1",
        "part": "Coupling capacitor",
        "value": "0.1 µF",
        "role": "Tone-stack bass cap, slope node to the bass pot"
      },
      {
        "ref": "CB2",
        "part": "Coupling capacitor",
        "value": "0.047 µF",
        "role": "Tone-stack middle-leg cap, slope node to the bleed resistor"
      },
      {
        "ref": "RBL",
        "part": "Carbon comp resistor",
        "value": "6.8 kΩ · ½ W",
        "role": "Tone-stack bleed resistor"
      },
      {
        "ref": "VRT",
        "part": "Audio-taper potentiometer",
        "value": "250 kΩ-A",
        "role": "Treble"
      },
      {
        "ref": "VRB",
        "part": "Audio-taper potentiometer",
        "value": "250 kΩ-A",
        "role": "Bass"
      },
      {
        "ref": "VRV",
        "part": "Audio-taper potentiometer",
        "value": "1 MΩ-A",
        "role": "Volume"
      },
      {
        "ref": "RL1B",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "V1B plate load"
      },
      {
        "ref": "RK1B",
        "part": "Carbon comp resistor",
        "value": "1.5 kΩ · ½ W",
        "role": "V1B cathode bias"
      },
      {
        "ref": "CK1B",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "V1B cathode bypass"
      },
      {
        "ref": "R47",
        "part": "Carbon comp resistor",
        "value": "47 Ω · ½ W",
        "role": "V1B cathode tail — the feedback injection point"
      },
      {
        "ref": "RNFB",
        "part": "Carbon comp resistor",
        "value": "2.7 kΩ · ½ W",
        "role": "Negative feedback, speaker to the 47 Ω tail"
      },
      {
        "ref": "CC1",
        "part": "Coupling capacitor",
        "value": "0.022 µF",
        "role": "V1B plate → inverter grid"
      },
      {
        "ref": "RGPI",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Inverter grid leak, returned to the tail junction"
      },
      {
        "ref": "RLPI",
        "part": "Carbon comp resistor",
        "value": "56 kΩ · ½ W",
        "role": "Inverter plate load"
      },
      {
        "ref": "RKPI",
        "part": "Carbon comp resistor",
        "value": "1 kΩ · ½ W",
        "role": "Inverter cathode resistor"
      },
      {
        "ref": "RTAIL",
        "part": "Carbon comp resistor",
        "value": "56 kΩ · ½ W",
        "role": "Inverter tail (junction → ground)"
      },
      {
        "ref": "C1",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "Inverter plate → V3 grid"
      },
      {
        "ref": "C2",
        "part": "Coupling capacitor",
        "value": "0.1 µF · 400 V",
        "role": "Inverter cathode → V4 grid"
      },
      {
        "ref": "RTO",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W",
        "role": "Oscillator plate load, from the screen rail"
      },
      {
        "ref": "RKTO",
        "part": "Carbon comp resistor",
        "value": "3.3 kΩ · ½ W",
        "role": "Oscillator cathode bias"
      },
      {
        "ref": "CKTO",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 25 V",
        "role": "Oscillator cathode bypass"
      },
      {
        "ref": "CTO1",
        "part": "Film capacitor",
        "value": "0.02 µF",
        "role": "Phase-shift cap, plate to the first network node"
      },
      {
        "ref": "CTO2",
        "part": "Film capacitor",
        "value": "0.01 µF",
        "role": "Phase-shift cap, second section"
      },
      {
        "ref": "CTO3",
        "part": "Film capacitor",
        "value": "0.01 µF",
        "role": "Phase-shift cap, third section (to grid)"
      },
      {
        "ref": "RTO1",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Phase-shift resistor, returned to the oscillator cathode"
      },
      {
        "ref": "RTO2",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Phase-shift resistor, grid to ground"
      },
      {
        "ref": "VRSPD",
        "part": "Reverse-audio potentiometer",
        "value": "3 MΩ-RA",
        "role": "Speed"
      },
      {
        "ref": "RSPD",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W",
        "role": "Speed-network series resistor to ground"
      },
      {
        "ref": "RTOUT",
        "part": "Carbon comp resistor",
        "value": "1 MΩ · ½ W",
        "role": "Oscillator output series resistor"
      },
      {
        "ref": "CTOUT1",
        "part": "Film capacitor",
        "value": "0.02 µF",
        "role": "Oscillator output shunt to ground"
      },
      {
        "ref": "CTOUT2",
        "part": "Coupling capacitor",
        "value": "0.1 µF",
        "role": "Oscillator output coupling into the intensity control"
      },
      {
        "ref": "VRINT",
        "part": "Linear potentiometer",
        "value": "250 kΩ-L",
        "role": "Intensity — taps the bias line"
      },
      {
        "ref": "JVIB",
        "part": "Jack",
        "value": "single-pole footswitch",
        "role": "Vibrato pedal — grounds the phase-shift ladder's middle node (CTO2 / CTO3 / RTO1) to stop the oscillator"
      },
      {
        "ref": "RGL1",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W · 5%",
        "role": "V3 grid leak, from the −34 V bias line"
      },
      {
        "ref": "RGL2",
        "part": "Carbon comp resistor",
        "value": "220 kΩ · ½ W · 5%",
        "role": "V4 grid leak, from the −34 V bias line"
      },
      {
        "ref": "TR2",
        "part": "Output transformer",
        "value": "Fender 125A10B",
        "role": "Push-pull 6V6 output"
      },
      {
        "ref": "JSPK",
        "part": "Jack",
        "value": "speaker + external speaker",
        "role": "Output-transformer secondary"
      },
      {
        "ref": "TR1",
        "part": "Power transformer",
        "value": "Fender 125P1B · 340-0-340 V",
        "role": "HT + heaters + rectifier filament"
      },
      {
        "ref": "CA",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 450 V",
        "role": "Reservoir filter, +420 V node"
      },
      {
        "ref": "CB",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 450 V",
        "role": "Filter, screen rail (+415 V)"
      },
      {
        "ref": "CC",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 450 V",
        "role": "Filter, node between the two 18 kΩ droppers"
      },
      {
        "ref": "CD",
        "part": "Electrolytic capacitor",
        "value": "20 µF · 450 V",
        "role": "Filter, preamp and inverter rail (+290 V)"
      },
      {
        "ref": "RD1",
        "part": "Wirewound resistor",
        "value": "1 kΩ · 1 W",
        "role": "Rail dropper, reservoir → screens"
      },
      {
        "ref": "RD2",
        "part": "Wirewound resistor",
        "value": "18 kΩ · 1 W",
        "role": "Rail dropper, screens → intermediate node"
      },
      {
        "ref": "RD3",
        "part": "Wirewound resistor",
        "value": "18 kΩ · 1 W",
        "role": "Rail dropper, intermediate node → preamp rail"
      },
      {
        "ref": "FUSE",
        "part": "Fuse",
        "value": "1 A slo-blo",
        "role": "Mains"
      },
      {
        "ref": "SW1",
        "part": "Switch",
        "value": "SPST",
        "role": "AC switch"
      },
      {
        "ref": "SW2",
        "part": "Switch",
        "value": "3-position",
        "role": "Ground switch (period part)"
      },
      {
        "ref": "CDEATH",
        "part": "Ceramic capacitor",
        "value": "0.047 µF · 600 V",
        "role": "Ground-switch cap (period; not in modern builds)"
      },
      {
        "ref": "RBF",
        "part": "Carbon comp resistor",
        "value": "100 kΩ · ½ W · 5%",
        "role": "Bias-supply feed from the HT winding (the layout prints '100K 5%')"
      },
      {
        "ref": "DBIAS",
        "part": "Rectifier (bias)",
        "value": "silicon diode",
        "role": "Bias-supply rectifier"
      },
      {
        "ref": "RB",
        "part": "Carbon comp resistor",
        "value": "27 kΩ · ½ W",
        "role": "Bias-supply bleeder"
      },
      {
        "ref": "CBIAS",
        "part": "Electrolytic capacitor",
        "value": "25 µF · 50 V",
        "role": "Bias-supply filter"
      },
      {
        "ref": "V1",
        "part": "Preamp tube",
        "value": "12AX7 (7025)",
        "role": "Both gain stages (V1A, V1B)"
      },
      {
        "ref": "V2",
        "part": "Preamp tube",
        "value": "12AX7",
        "role": "Tremolo oscillator (V2A) + cathodyne phase inverter (V2B)"
      },
      {
        "ref": "V3",
        "part": "Power tube",
        "value": "6V6GT",
        "role": "Push-pull output, inverter-plate side"
      },
      {
        "ref": "V4",
        "part": "Power tube",
        "value": "6V6GT",
        "role": "Push-pull output, inverter-cathode side"
      },
      {
        "ref": "V5",
        "part": "Rectifier tube",
        "value": "GZ34",
        "role": "Full-wave rectifier"
      }
    ]
  },
  "publishedVoltages": {
    "source": "Fender Princeton-Amp AA964 schematic, printed voltages: +420 (reservoir, OT centre tap, 6V6 plates), +415 (6V6 screens), +290 (preamp and phase-inverter rail), +190 (both 7025 plates), +1.5 (both 7025 cathodes), +220/+65/+63.8 (cathodyne plate, cathode, junction), +260/+2.4 (tremolo oscillator, excluded), -34 (6V6 fixed bias). The layout sheet adds +370 at the intermediate filter node.",
    "nodes": {
      "BA": {
        "chart": 415,
        "tol_pct": 8,
        "note": "6V6 screen rail, derived from +420 through the 1 kΩ · 1 W dropper"
      },
      "BB": {
        "chart": 290,
        "tol_pct": 8,
        "note": "preamp and phase-inverter rail, derived through both 18 kΩ · 1 W droppers"
      },
      "P1A": {
        "chart": 190,
        "tol_pct": 20,
        "note": "first-stage plate, 100 kΩ from the +290 rail"
      },
      "K1A": {
        "chart": 1.5,
        "tol_pct": 20,
        "note": "first-stage cathode over 1.5 kΩ (25 µF bypass)"
      },
      "P1B": {
        "chart": 190,
        "tol_pct": 20,
        "note": "second-stage plate, 100 kΩ from the +290 rail"
      },
      "K1B": {
        "chart": 1.5,
        "tol_pct": 20,
        "note": "second-stage cathode pin, above the 1.5 kΩ; the 47 Ω feedback tail and the 2.7 kΩ loop resistor sit below it"
      },
      "PPI": {
        "chart": 220,
        "tol_pct": 20,
        "note": "cathodyne plate, 56 kΩ load from the +290 rail"
      },
      "KPI": {
        "chart": 65,
        "tol_pct": 20,
        "note": "cathodyne cathode pin, top of the 1 kΩ"
      },
      "JPI": {
        "chart": 63.8,
        "tol_pct": 20,
        "note": "cathodyne junction (1 kΩ / 56 kΩ), the grid-leak return"
      },
      "G61": {
        "chart": -34,
        "tol_pct": 8,
        "note": "6V6 grids, fixed bias through the 220 kΩ leaks from the −34 V line"
      },
      "J1B": {
        "chart": null,
        "note": "second-stage feedback tail (47 Ω in parallel with the 2.7 kΩ loop resistor) — the drawing prints no value at this node"
      },
      "BINT": {
        "chart": 370,
        "tol_pct": 8,
        "note": "node between the two 18 kΩ droppers. The schematic prints no value here, but the LAYOUT sheet labels this filter-can section +370 V — so this rail is compared, not merely reported"
      }
    }
  },
  "operatingPoint": [
    {
      "node": "BA",
      "chart": 415,
      "sim": 411.998,
      "disputed": false,
      "dev_pct": 0.7233734939759059,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "6V6 screen rail, derived from +420 through the 1 kΩ · 1 W dropper",
      "dispute_note": ""
    },
    {
      "node": "BB",
      "chart": 290,
      "sim": 297.054,
      "disputed": false,
      "dev_pct": 2.4324137931034393,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "preamp and phase-inverter rail, derived through both 18 kΩ · 1 W droppers",
      "dispute_note": ""
    },
    {
      "node": "P1A",
      "chart": 190,
      "sim": 194.639,
      "disputed": false,
      "dev_pct": 2.441578947368426,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "first-stage plate, 100 kΩ from the +290 rail",
      "dispute_note": ""
    },
    {
      "node": "K1A",
      "chart": 1.5,
      "sim": 1.536,
      "disputed": false,
      "dev_pct": 2.400000000000002,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "first-stage cathode over 1.5 kΩ (25 µF bypass)",
      "dispute_note": ""
    },
    {
      "node": "P1B",
      "chart": 190,
      "sim": 196.094,
      "disputed": false,
      "dev_pct": 3.207368421052628,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "second-stage plate, 100 kΩ from the +290 rail",
      "dispute_note": ""
    },
    {
      "node": "K1B",
      "chart": 1.5,
      "sim": 1.561,
      "disputed": false,
      "dev_pct": 4.066666666666663,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "second-stage cathode pin, above the 1.5 kΩ; the 47 Ω feedback tail and the 2.7 kΩ loop resistor sit below it",
      "dispute_note": ""
    },
    {
      "node": "PPI",
      "chart": 220,
      "sim": 232.14,
      "disputed": false,
      "dev_pct": 5.518181818181811,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "cathodyne plate, 56 kΩ load from the +290 rail",
      "dispute_note": ""
    },
    {
      "node": "KPI",
      "chart": 65,
      "sim": 66.073,
      "disputed": false,
      "dev_pct": 1.6507692307692206,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "cathodyne cathode pin, top of the 1 kΩ",
      "dispute_note": ""
    },
    {
      "node": "JPI",
      "chart": 63.8,
      "sim": 64.914,
      "disputed": false,
      "dev_pct": 1.7460815047022011,
      "tol_pct": 20,
      "gated": true,
      "within": true,
      "note": "cathodyne junction (1 kΩ / 56 kΩ), the grid-leak return",
      "dispute_note": ""
    },
    {
      "node": "G61",
      "chart": -34,
      "sim": -34,
      "disputed": false,
      "dev_pct": 0,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "6V6 grids, fixed bias through the 220 kΩ leaks from the −34 V line",
      "dispute_note": ""
    },
    {
      "node": "J1B",
      "chart": null,
      "sim": 0.047,
      "disputed": false,
      "dev_pct": null,
      "tol_pct": 5,
      "gated": false,
      "within": null,
      "note": "second-stage feedback tail (47 Ω in parallel with the 2.7 kΩ loop resistor) — the drawing prints no value at this node",
      "dispute_note": ""
    },
    {
      "node": "BINT",
      "chart": 370,
      "sim": 354.526,
      "disputed": false,
      "dev_pct": 4.182162162162159,
      "tol_pct": 8,
      "gated": true,
      "within": true,
      "note": "node between the two 18 kΩ droppers. The schematic prints no value here, but the LAYOUT sheet labels this filter-can section +370 V — so this rail is compared, not merely reported",
      "dispute_note": ""
    }
  ],
  "checks": [
    {
      "id": "dc",
      "title": "DC operating point",
      "status": "Verified",
      "summary": "11 reference nodes are within tolerance. Maintainer verification is recorded for 2026-08-02; changes since then are awaiting maintainer re-review.",
      "details": [
        "The circuit's facts (netlist, reference voltages, parts list, both drawings' connections, capacitor polarity marks and heater declarations) have changed since the maintainer's review, or no review fingerprint is on record yet. The badge stands on its date until the maintainer re-reviews.",
        "This compares simulated DC conditions with the cited reference. It does not test sound, physical construction or every part of the circuit."
      ],
      "tone": "checked"
    },
    {
      "id": "schematic",
      "title": "Schematic against DC model",
      "status": "Checked",
      "summary": "Connectivity of modelled components is checked on every change.",
      "details": [
        "Parts outside the DC model need separate checks and source review."
      ],
      "tone": "checked"
    },
    {
      "id": "board",
      "title": "Board against DC model",
      "status": "Checked",
      "summary": "Connectivity of modelled components is checked on every change.",
      "details": [
        "This does not establish heater wiring or physical spacing."
      ],
      "tone": "checked"
    },
    {
      "id": "drawings",
      "title": "Schematic against board",
      "status": "No open findings",
      "summary": "No disagreement is listed in the published comparison.",
      "details": [
        "A finding identifies a difference or a coverage gap. The factory source must decide which drawing, if either, needs correction.",
        "9 sheet-only parts are explicitly excluded: CBIAS, CDEATH, DBIAS, FUSE, R1n, R2n, RB, RBF, RG1A. Heaters and the pilot lamp are checked separately."
      ],
      "tone": "checked"
    },
    {
      "id": "heaters",
      "title": "Heater and filament wiring",
      "status": "Checked",
      "summary": "The declared heater circuits cover the drawing and pass their separate wiring check.",
      "details": [],
      "tone": "checked"
    },
    {
      "id": "polarity",
      "title": "Capacitor polarity",
      "status": "Partial",
      "summary": "1 capacitor marking cannot be confirmed by the DC model.",
      "details": [
        "CKTO: CKTO.a: reaches only ground, through RKTO"
      ],
      "tone": "attention"
    }
  ],
  "corrections": [
    {
      "id": "aa964-input-2026-10-03",
      "date": "2026-10-03",
      "amps": [
        "aa964"
      ],
      "title": "AA964 input grid leak and vibrato footswitch",
      "description": "The 1 MΩ input leak now hangs from jack 1's tip, as the factory drawing shows; it had been drawn on the grid. The bias-feed resistor carries its printed 5 % tolerance, and the vibrato footswitch is described as grounding the phase-shift ladder's middle node. No operating point changes.",
      "commit": "46a9e3eb7cdf7b3ea8f7d4de75efb4fcd353301a",
      "url": "https://github.com/TheAnalogMaker/circuit-codex/commit/46a9e3eb7cdf7b3ea8f7d4de75efb4fcd353301a"
    }
  ],
  "sourceDirectory": "https://github.com/TheAnalogMaker/circuit-codex/tree/ebddc3fd2cf887dca010bbe60487d7391ea6c052/amps/aa964"
}