TL Audio C1 Valve Compressor

{
  "schema_version": "capability-outboard-v1",
  "id": "tl-audio-c1",
  "name": "TL Audio C1 Valve Compressor",
  "maker": "TL Audio (Tony Larking Professional Sales Ltd., Letchworth, England)",
  "clone_of": null,
  "clone_of_note": "Original TL Audio design (Tony Larking Professional Sales, UK). Not a clone or homage. Marketed as 'Valve Compressor'; combines a triode valve voltage amplifier with solid-state input/output stages and a solid-state sidechain detector that feeds the valve compressor stage.",
  "device_class": "channel_strip",
  "device_class_subtypes": [
    "preamp",
    "compressor"
  ],
  "device_class_subtypes_note": "Multi-class outboard per the capability-outboard-v1 §C rule. The C1 is marketed primarily as a 'Valve Compressor' but each channel exposes a full mic+line preamp stage with phantom power, an aux instrument input, a switchable HPF, the valve gain stage, AND the valve compressor section -- the preamp + compressor combination on one channel is the channel_strip archetype. No EQ section on the C1 (the C2 sibling device adds EQ); the only frequency-shaping is the 90 Hz HPF documented under params.preamp.",
  "topology": "hybrid valve/solid-state -- solid-state input amp + triode valve voltage amplifier + solid-state sidechain detector + second triode valve in compressor signal path",
  "topology_note": "Manual p.3 Introduction: 'A solid state, electronically balanced input amplifier is used, to achieve state of the art performance with very low noise, low distortion and wide bandwidth ... A triode valve is used as a second stage voltage amplifier, to obtain the classic valve sound and gradual overdrive characteristics ... The sidechain processing is solid state, whilst a second triode valve stage is employed in the compressor circuit'. Output stage is 'solid state, electronically balanced output stage with XLR connector'. Two triode valves per channel; solid-state I/O.",
  "channels": 2,
  "linkable": true,
  "linkable_note": "Manual p.13 Stereo Operation: 'In normal 2 channel operation, the controls operate independently for each channel. The compressor may also be set for full stereo operation, where the Threshold, Attack, Release and Ratio controls for channel A control both channels. The input gain and gain make-up controls remain separate to allow relative input/output gain balance adjustment.' Control voltages are linked in stereo mode to preserve stereo image during gain reduction.",
  "params": {
    "preamp": {
      "gain_range_db": "mic: +16..+60, line: -10..+35",
      "gain_range_db_note": "Manual p.14 Specifications: Mic Input 'Gain range +16 to +60dB'; Line Input 'Gain range -10dB to +35dB, suitable for nominal input levels from -20dBu to +20dBu'. Single front-panel gain control per channel; the active input is selected via the input selector switch.",
      "phantom_48v": true,
      "phantom_48v_note": "Manual p.11 + p.14: '48V phantom power available, indicated by red LED'. Engaged via the input selector switch position 'Mic+48V'. Per channel.",
      "pad_db": null,
      "pad_db_note": "No dedicated input pad. Attenuation below 0 dB at line level is via the -10 dB end of the line gain control.",
      "polarity_invert": false,
      "polarity_invert_note": "No front-panel polarity invert switch documented on the C1.",
      "hpf_hz": 90,
      "hpf_hz_note": "Manual p.3 + p.14: 'switchable second order high pass filter, -3dB at 90Hz, to remove unwanted LF noise'. Engaged via front-panel HPF switch (per channel). 2nd-order = -12 dB/octave slope (manual p.14).",
      "inst_input": true,
      "inst_input_note": "Manual p.11 + p.14: 'front panel mounted auxiliary jack socket for each channel allows mic or line level inputs to be easily connected to the compressor. The aux input may be used for a stereo keyboard or mono guitar'. Switchable input level: 'Keyboard' (high) vs 'Guitar' (low pickup). Aux A normals to Aux B for mono-to-stereo splitting.",
      "transformer_coupled": false,
      "transformer_coupled_note": "Solid-state electronically-balanced I/O per manual p.3 Introduction; no input or output transformers. The 'valve' character is in the second voltage-amplifier stage and the compressor signal-path stage, not the I/O."
    },
    "compressor": {
      "threshold_db": "-20..+20",
      "threshold_db_note": "Manual p.12 + p.15: 'variable threshold, set by a rotary control calibrated from +20dBu to -20dBu, resulting in increased compression as the control is rotated clockwise'.",
      "ratio": "1.5:1..30:1",
      "ratio_note": "Manual p.13 + p.15: 'The ratio may be varied from 1:1.5 (very gentle compression) to 1:30 (near limiting)'. Note the manual writes ratios as 1:1.5 / 1:30 -- typo of typical convention; capability records as 1.5:1 / 30:1 (input-to-output convention used by the schema).",
      "attack": "0.5..50 ms",
      "attack_note": "Manual p.12 + p.15: 'attack time is variable from 0.5msec to 50msec. At 0.5msec attack, the compressor is fast enough to reduce the gain of a 1KHz signal in less than half a cycle'.",
      "release": "40..4000 ms",
      "release_note": "Manual p.12 + p.15: 'release time is variable from 40msec to approximately 4 seconds'. Time constants become signal-dependent during very short transients (program-dependent modification, manual p.12), so the front-panel controls are calibrated 'fast' to 'slow' rather than absolute values.",
      "knee": "soft",
      "knee_note": "Manual p.13: 'The compressor normally operates with a soft-knee, i.e. the compression is gradually introduced as the signal passes the threshold, in which case the ratio refers to the compression eventually obtained'. Soft-knee is the only available characteristic (no hard/soft switch).",
      "makeup_gain": true,
      "makeup_gain_note": "Per-channel makeup gain. Manual p.13 + p.15: 'Gain Make-Up: Up to 20dB of gain make-up may be applied, to retain the subjective loudness of the signal'. In stereo mode the makeup-gain stays per-channel (manual p.13) to allow input/output gain balance adjustment.",
      "output_gain_db": "0..+20",
      "output_gain_db_note": "Manual p.15: 'Gain Make-Up 0 to +20dB'.",
      "auto_mode": false,
      "auto_mode_note": "No Adaptive / Auto switch. The C1 has built-in signal-dependent variation of attack/release time constants for short transients (manual p.12) but this is automatic and not user-switchable.",
      "sidechain_external": true,
      "sidechain_external_note": "Manual p.3 + p.6 + p.17: 'An insertion point is provided in the sidechain circuit to allow an equaliser or other processor to be used for frequency conscious compression'. Per channel. Insert is unbalanced TRS, tip=send, ring=return, sleeve=ground, nominal level -2 dBu.",
      "sidechain_filter": null,
      "sidechain_filter_note": "No built-in sidechain filter; the external sidechain insert point allows an external EQ to be patched for frequency-conscious compression.",
      "gain_reduction_meter_stages": null,
      "gain_reduction_meter_stages_note": "Compression display uses the same analog VU meter as the output-level display (switchable). Not an LED ladder; no discrete stage count."
    }
  },
  "io": {
    "audio_in": {
      "format": [
        "xlr",
        "ts"
      ],
      "balanced": true,
      "impedance_ohms": null,
      "impedance_ohms_note": "Per-input-type impedance varies (manual p.14): Mic XLR >10 kΩ (to suit 150-600 Ω mics); Line XLR >5 kΩ; Unbalanced Line 1/4\" >5 kΩ; Aux 1/4\" (impedance not specified explicitly). Single int field doesn't fit the multi-input design.",
      "inst_zi": true,
      "inst_zi_note": "Front-panel auxiliary 1/4\" TS jack per channel. Switchable level: 'Keyboard' (high) for line-level keys, 'Guitar' (low) for pickup-level guitar. Aux A normals to Aux B for mono-to-stereo distribution (manual p.11). Two XLR inputs per channel (one for mic, one for line) live on the rear panel."
    },
    "audio_out": {
      "format": [
        "xlr",
        "ts"
      ],
      "balanced": true,
      "impedance_ohms": 10,
      "impedance_ohms_note": "Manual p.15: 'Output impedance less than 10 ohms'. XLR balanced electronically + 1/4\" TS unbalanced jack (impedance 47 Ω, manual p.15)."
    },
    "sidechain": {
      "send": true,
      "return": true,
      "format": "trs",
      "format_note": "Manual p.6 + p.17: 'switched 3 pin, 0.25\" switched jack socket on the rear of the unit ... Sleeve = Ground, Tip = Send, Ring = Return ... Nominal level -2dBu. Output impedance 47 Ω, Return input impedance 10 kΩ'. Per channel.",
      "per_channel": true
    },
    "stereo_link": true,
    "bypass": "electronic",
    "bypass_note": "Manual p.3 Introduction: 'The compressors may be by-passed for A-B comparison'. Front-panel COMP IN/OUT switch per channel (electronic bypass, not relay). Mains On/Off does not engage a hard-wired bypass on the C1 (unlike the Mindprint T-Comp).",
    "operating_level": [
      "+4dBu",
      "-10dBV"
    ],
    "operating_level_note": "Manual p.7 + p.15: 'Rear panel selectable for +4dBu or -10dBu nominal level'. Switch should be set to the position that 'results in the best signal to noise ratio, whilst preserving sufficient headroom'.",
    "rack_format": "2U",
    "rack_format_note": "Manual p.15: '19\" rack mounting, 2U high. 483mm wide x 88mm high x 205mm deep. Weight: 6Kg.'"
  },
  "meters": [
    {
      "kind": "vu",
      "stages": null,
      "range_db": "-20..+3 VU (analog needle)",
      "shared": false,
      "_note": "Manual p.13 + p.15: 'twin, illuminated VU meters ... calibrated for 0VU = +4dBu' (one per channel). Switchable between output-level and gain-reduction modes via front-panel METER switch. In GR mode, 0dB indicates no compression; the needle deflects to show the amount of GR. The reference point '0VU = +4dBu' is the manufacturer default and may be internally adjusted by a dealer. Analog VU meters have no discrete stage count (stages=null)."
    }
  ],
  "performance": {
    "bypass_per_channel": true,
    "bypass_per_channel_note": "Per-channel COMP IN/OUT bypass for A-B comparison (manual p.3 Introduction). The bypass is at the compressor section -- preamp + valve gain stage remain in the signal path when compression is bypassed.",
    "auto_release": false
  },
  "provenance": {
    "manual_path": "manuals/preamp-outboard--tl-audio-c1-manual.pdf",
    "confidence": "high",
    "last_verified": "2026-05-27",
    "manual_pages": [
      3,
      6,
      7,
      11,
      12,
      13,
      14,
      15,
      17
    ],
    "verify_via": "SM46 single-seat manual extraction. P8 rack-tier completion (4-device cluster).",
    "verify_note": "Manual-grounded extraction from manuals/preamp-outboard--tl-audio-c1-manual.pdf. The C1 is a 2-channel valve-hybrid channel strip: solid-state I/O + triode-valve voltage amplifier + solid-state sidechain detector + second valve stage in the compressor signal path. Classified as channel_strip with subtypes [preamp, compressor] (no EQ on the C1; the HPF is documented under params.preamp.hpf_hz). Compressor section has external sidechain insert (TRS combined send/return) which differs from dbx 1066 (separate TRS send + TS return jacks) -- both fit the io.sidechain.format='trs' encoding. Mic input has a real preamp with +16..+60 dB gain (UNLIKE the Mindprint T-Comp's line-only design), supporting Adam's framing of the C1 as a 'full channel strip' relative to T-Comp's 'compressor + tube' framing. The unit's twin VU meters are single physical meters per channel switchable between output-level and GR display; modeled as one meter entry with kind=vu and the dual-mode behaviour described in the note (compressor.gain_reduction_meter_stages=null because the same VU shows GR, no discrete LED-stage count).",
    "fields": {
      "device_class": {
        "conf": "high",
        "pg": 3
      },
      "device_class_subtypes": {
        "conf": "high",
        "pg": 3
      },
      "topology": {
        "conf": "high",
        "pg": 3
      },
      "channels": {
        "conf": "high",
        "pg": 3
      },
      "linkable": {
        "conf": "high",
        "pg": 13
      },
      "params.preamp.gain_range_db": {
        "conf": "high",
        "pg": 14
      },
      "params.preamp.phantom_48v": {
        "conf": "high",
        "pg": 11
      },
      "params.preamp.hpf_hz": {
        "conf": "high",
        "pg": 14
      },
      "params.preamp.inst_input": {
        "conf": "high",
        "pg": 11
      },
      "params.preamp.transformer_coupled": {
        "conf": "high",
        "pg": 3
      },
      "params.compressor.threshold_db": {
        "conf": "high",
        "pg": 15
      },
      "params.compressor.ratio": {
        "conf": "high",
        "pg": 15
      },
      "params.compressor.attack": {
        "conf": "high",
        "pg": 15
      },
      "params.compressor.release": {
        "conf": "high",
        "pg": 15
      },
      "params.compressor.knee": {
        "conf": "high",
        "pg": 13
      },
      "params.compressor.makeup_gain": {
        "conf": "high",
        "pg": 13
      },
      "params.compressor.output_gain_db": {
        "conf": "high",
        "pg": 15
      },
      "params.compressor.sidechain_external": {
        "conf": "high",
        "pg": 3
      },
      "io.audio_in.format": {
        "conf": "high",
        "pg": 5
      },
      "io.audio_out.format": {
        "conf": "high",
        "pg": 7
      },
      "io.audio_out.impedance_ohms": {
        "conf": "high",
        "pg": 15
      },
      "io.sidechain.send": {
        "conf": "high",
        "pg": 17
      },
      "io.sidechain.return": {
        "conf": "high",
        "pg": 17
      },
      "io.sidechain.format": {
        "conf": "high",
        "pg": 17
      },
      "io.sidechain.per_channel": {
        "conf": "high",
        "pg": 6
      },
      "io.stereo_link": {
        "conf": "high",
        "pg": 13
      },
      "io.bypass": {
        "conf": "high",
        "pg": 3
      },
      "io.operating_level": {
        "conf": "high",
        "pg": 7
      },
      "io.rack_format": {
        "conf": "high",
        "pg": 15
      },
      "meters.0.kind": {
        "conf": "high",
        "pg": 13
      }
    }
  }
}