IGS Audio Tubecore is a dual-channel stereo vari-mu compressor in a 3U chassis — designed from the ground up as a studio mastering compressor. The signal path is fully symmetric from input to output, with Carnhill and Sowter transformers, 1% metal film resistors, Wima capacitors, and NOS 6N1P-EW tubes individually calibrated per unit. The 3U enclosure provides panel clarity and rear access to the tube slots; all controls run on 24-position Elma switches. Operating modes include Dual Mono and Mid/Side, with a sidechain HPF, Wet/Dry Mixer, and two independent bypass switches per channel for A/B comparison.
Vari-Mu and Swappable Tubes — Four Compression Characters
Vari-mu compression works by varying the operating point of the triode via the sidechain voltage — the higher the input level, the more the tube is driven into cutoff, the greater the gain reduction. No hard threshold, no stepped knee: vari-mu compresses smoothly, musically, and with harmonically rich distortion that listeners describe as dense, alive, and cohesive. The Tubecore accepts four tube families in the gain-control stage: 6N1P-EW NOS (standard IGS set — "standard IGS compression"), 6BC8/6BZ8 ("tight, transparent, punchy"), 6386 ("legendary compression, famous twin triode"), and 5670 ("deep and dark tube compression"). Each choice physically changes attack character, release behavior, and harmonic profile without any circuit modification — tube swapping is a user procedure described in the manual, performed via the rear panel.
M/S, Sidechain HPF, Wet/Dry and Gain Staging
Mid/Side mode via OpAmp encoder/decoder enables independent compression of the center and side channels — a precise mastering tool for managing stereo width without disturbing the overall tonal balance. The sidechain HPF (60 Hz / 120 Hz / Off) decouples low-frequency content from the compression control circuit, eliminating pumping on material with prominent kick drum or bass. The Wet/Dry control implements parallel compression inline without external routing. Per-channel gain staging: Input (1–24 dB) → Threshold (0 to –12 dB reduction) → Output (1–24 dB) → Wet/Dry — all controls stepped. Two hardwire bypass positions per channel allow instant A/B comparison without touching the settings. Maximum gain reduction is 20 dB, dynamic range above 107 dB(A).
KEY FEATURES
- Dual-channel stereo vari-mu compressor, 3U 19" format
- Fully symmetric signal path from input to output
- Transformers: Carnhill and Sowter (input and output)
- NOS 6N1P-EW tubes (standard); optional 6BC8/6BZ8, 6386, 5670 — user-replaceable
- 1% metal film resistors, Wima capacitors; components matched per unit
- Input Gain: 1–24 dB (stepped, 24-position Elma)
- Output Gain: 1–24 dB (stepped, 24-position Elma)
- Threshold: 0 to –12 dB reduction
- Attack: 0.1 / 0.3 / 1 / 3 / 10 / 30 ms (stepped)
- Release: 0.1 / 0.4 / 0.6 / 0.8 / 1.6 s / Auto (stepped)
- Max gain reduction: 20 dB
- Sidechain HPF: 60 Hz / 120 Hz / Off
- Wet/Dry Mixer: 0–100%, 4 dB steps
- Dual Mono or Mid/Side mode (OpAmp encoder/decoder)
- Two hardwire bypass positions per channel (fast A/B)
- Input impedance: 2500 Ω; output impedance: 600 Ω (balanced XLR)
- Max input/output: +22 dBu; dynamic range: >107 dB(A)
- VU metering: fast analog VU per channel
- Internal power supply; handmade in Poland
TECHNICAL SPECIFICATIONS
- Type: dual-channel stereo vari-mu compressor, 3U 19"
- Input impedance: 2500 Ω (transformer, balanced XLR)
- Output impedance: 600 Ω (transformer, balanced XLR)
- Operating level: +4 dBu
- Max input level: +22 dBu
- Max output level: +22 dBu
- Dynamic range: >107 dB(A)
- Max gain reduction: 20 dB
- Attack: 0.1 / 0.3 / 1 / 3 / 10 / 30 ms
- Release: 0.1 / 0.4 / 0.6 / 0.8 / 1.6 s / Auto
- Frequency response: 20 Hz – 20 kHz, ±0.2 dB
- Tubes: 6N1P-EW NOS (standard); optional 6BC8/6BZ8, 6386, 5670
- Transformers: Carnhill + Sowter
- Sidechain HPF: 60 Hz / 120 Hz / Off
- Wet/Dry: 0–100%, 4 dB steps
- M/S Processing: OpAmp encoder/decoder
- Bypass: hardwire, 2 positions per channel
- All controls: 24-position Elma switches
- Made in: Poland
