Dark2A

Dark2A — Tube Optical Leveling Amplifier

A schematic-accurate emulation of the legendary Teletronix LA-2A — the smoothest, most musical vocal and bass compressor ever built. Authentic T4B electro-optical attenuator, 12AX7 tube gain stage, and UTC HA-100X output transformer modeling, calibrated against the original hardware spec.

Topology:

• T4B Photocell — dual-stage release with program dependency (the signature LA-2A “self-adjusting” feel)
• 12AX7 tube gain stage with authentic harmonic profile
• UTC HA-100X output transformer modeling
• 18 Hz sidechain HPF (LA-2A 15 Hz spec)
• Always-on R30/C6 sidechain tilt (intrinsic to the LA-2A schematic, independent of HF Emphasis)
• 30 ms RMS detector, 450 ms GR decay, 3 s slow release — calibrated for the relaxed, “rounded” LA-2A response
• Peak Reduction tuned to pin the needle at 20 VU on typical program material
• x2 / x4 / x8 Kaiser FIR oversampling

Core controls (LA-2A faithful):

• Gain (0–40 dB) and Peak Reduction (0–100)
• Compress / Limit mode toggle (the original front-panel switch)
• HF Emphasis sidechain tilt (R37 emphasis circuit)
• Stereo Link for L/R coupling
• Mix for parallel compression

Pro extras:

• 6-band Sidechain EQ with frequency-selective compression
• 6-band Output EQ post-compression
• Knee, Input Gain, Saturation, Output Gain
• Three optional transformers: Carnhill (gentle, balanced H2), Sowter, Cinemag