IGS Audio A-Type 525 - Discrete VCR Compressor (500 Series)
The IGS Audio A-Type 525 is a premium 500 Series discrete compressor/limiter inspired by the legendary American designs of the 1970s. Built entirely with through-hole components, it features a balanced SSM2141 input, custom IGS transformer-balanced output, and a second audio transformer in the feedback path driving a Voltage Controlled Resistor (VCR) for smooth, musical gain reduction. With unique “Compress” switching for simultaneous gain/threshold adjustment, separate threshold and output controls, two modes (Compressor 2:1 and Limiter 20:1), fast 15μs attack, four release times, and a dedicated de-esser mode, the A-Type 525 delivers vintage character and modern precision for vocals, drums, bass, guitars, and mix bus processing.
Discrete VCR Compression
The compression is achieved using a hand-matched VCR in the feedback loop, controlled by a negative voltage signal for transparent yet colored dynamics. The fixed ultra-fast 15μs attack captures transients with precision, while four selectable release times (0.1 s, 0.5 s, 1.5 s, 2.0 s) and the unique Compress switch allow quick setup without level jumps. The de-esser mode reduces sibilance effectively, making it a versatile tool for detailed vocal work.
Key Features of the IGS Audio A-Type 525
- Discrete through-hole VCA/VCR compressor in 500 Series format
- Balanced SSM2141 input and custom IGS transformer output
- Second transformer in feedback path for classic tone
- “Compress” switch adjusts gain and threshold simultaneously
- Separate Threshold and Output controls
- Two modes: Compressor (2:1) and Limiter (20:1)
- Fixed 15μs attack, four release times (0.1–2.0 s)
- Dedicated de-esser mode
- High headroom: +27 dBu input, +28 dBu output
- Stepped controls for precise recall
Technical Specifications
- Type: 500 Series discrete VCR compressor/limiter
- Input Impedance: 10 kΩ (balanced, SSM2141)
- Output Impedance: 75 Ω (balanced, custom transformer)
- Operating Level: +4 dBu
- Max Input Level: +27 dBu
- Max Output Level: +28 dBu
- Max Gain Reduction: -25 dB
- Max Gain: 25 dB
- Noise Level: -99 dBA
- Frequency Response: 8 Hz–20 kHz (±0.1 dB)
- THD+N: 0.014% (typical)
- Attack: 15 μs (fixed)
- Release: 0.1 s, 0.5 s, 1.5 s, 2.0 s
- Ratio: 2:1 (Compressor), 20:1 (Limiter)
- Power Consumption: 2.5 W
- Current Draw: Compatible with standard 500 Series racks
