The 825EQ is a stereo tube mastering equalizer in a 3U 19" chassis, built on the topology of Tim de Paravicini's EAR 825Q – one of the most sought-after and expensive mastering EQs of the past several decades. IGS Audio implements the design with a full tube signal path: three ECC88 valves per channel, three audio transformers per channel, and UTM transformer-balanced inputs and outputs throughout. Five bands per channel – two shelving filters and three bell filters – are controlled exclusively via 24-way ELMA switches. Proportional Q ranging from 0.3 to 6 means the filter curve narrows as gain increases, a behaviour characteristic of the best tube EQs that makes both subtle ±0.5 dB mastering moves and more pronounced tonal shaping sound natural and musical. The unit is available in two versions: 0.5 dB steps covering ±6 dB, or 1 dB steps covering ±12 dB.
No hardwire bypass – by design, not omission
The 825EQ has no hardwire bypass in the conventional sense. When all bands are switched off, the signal continues to pass through the transformers and valves. This is a deliberate circuit decision: the pair of UTM transformers at input and output, combined with six ECC88 tubes in the signal path, introduce depth, cohesion, and stereo width to the material regardless of any EQ moves. The act of passing audio through the 825EQ – without touching a single band – already changes the character of the master. ECC88 tubes can be swapped for 6N23P or 6N1P variants to shift the tonal signature from warmer and denser toward more open and transparent, depending on the project and source material.
Five bands with proportional Q across the full mastering workflow
Low shelf and high shelf handle the frequency extremes; three bell filters cover low-mid, mid, and high-mid. Every band has a fixed frequency selection set and a 24-way ELMA gain switch – session recall is exact and fast without photographing the panel or writing down positions. Dynamic range exceeds 107 dBA at 1 kHz, output impedance is 600 ohms, maximum output level +22 dBu. A linear power supply stabilises the operating conditions for the valves under full load. The 825EQ is aimed primarily at mastering and mix bus duties, but works equally well on stems and groups where more pronounced tonal shaping is required.
KEY FEATURES
- 5-band stereo tube mastering equalizer (EAR 825Q-style), 3U 19"
- Three ECC88 tubes per channel – swappable for 6N23P or 6N1P
- Three audio transformers per channel + UTM transformer-balanced I/O
- All 24-way ELMA switches throughout – full session recall
- Proportional Q: 0.3–6 (curve narrows as gain increases)
- Two versions: ±6 dB (0.5 dB steps) or ±12 dB (1 dB steps)
- No hardwire bypass – signal always passes through transformers and tubes
- Linear power supply
- Bands: low shelf, low-mid bell, mid bell, high-mid bell, high shelf
- Frequency range: 10 Hz – 50 kHz
TECHNICAL SPECIFICATIONS
- Type: stereo tube equalizer, 5-band (EAR 825Q-style)
- Format: 3U, 19"
- Tubes: 3x ECC88 per channel (optional 6N23P or 6N1P)
- Transformers: 3 audio per channel + UTM I/O
- Switches: ELMA, 24-way, all bands
- Q: proportional, 0.3–6
- Correction range: ±6 dB (0.5 dB steps) or ±12 dB (1 dB steps)
- Frequency range: 10 Hz – 50 kHz (±0.4 dB)
- Input impedance (balanced): 10 kΩ, IGS Custom Transformers / XLR
- Output impedance (balanced): 600 Ω, IGS Custom Transformers / XLR
- Operating level: +4 dBu
- Maximum output level: +22 dBu
- Dynamic range: above 107 dBA (1 kHz, +22 dBu)
- Bypass: no hardwire (signal passes through tubes and transformers)
- Power supply: linear
