Warm Audio WA-2A Tube Optical Compressor

The Warm Audio WA-2A is a single-channel tube optical compressor that reproduces the LA-2A, the most revered leveling amplifier in recording history. Featuring an all-discrete, Class A, all-tube circuit with four vacuum tubes, CineMag USA transformers, and a socketed Kenetek T4B optical attenuator, the WA-2A delivers gentle, musical compression with the streamlined two-knob operation that has defined this style of dynamics control for vocals, acoustic instruments, and bass.

Optical Compression

The WA-2A's compression character is governed by the Kenetek T4B optical attenuator module, which uses a light-dependent resistor to apply gain reduction. The attack, release, ratio, and knee are all determined by the interaction between the photocell and the incoming audio, producing the smooth, program-dependent compression that made the original a vocal tracking standard. A Compress/Limit switch changes the ratio from approximately 4:1 to near infinity, covering gentle leveling through hard limiting. The T4B module is socketed and compatible with T4A and T4C alternatives for different compression textures.

Controls and Metering

Peak Reduction sets the compression threshold on a percentage scale, with 100 delivering the full 40 dB of gain reduction. Output Gain provides up to 40 dB of makeup gain. The Pre-Emphasis knob functions as a sidechain tone control: at the center position, the detector responds to full-bandwidth peaks; rotating toward the high-pass position makes the compressor less sensitive to low frequencies and more responsive to high-frequency transients. A large VU meter displays gain reduction or output level, with a rear-panel calibration potentiometer.

Stereo Linking

A rear-panel TRS stereo link connector allows two WA-2A units to share threshold response for matched stereo compression. When linked, both units respond to the same sidechain signal, maintaining a stable stereo image under gain reduction.

Specifications

• Type: Single-channel tube optical compressor/leveling amplifier
• Topology: All-discrete, Class A, all-tube, hand-populated
• Tubes: 2x 12AX7, 1x 12BH7, 1x 6P1
• Transformers: CineMag USA (custom, large-core)
• Optical attenuator: Kenetek T4B (socketed, compatible with T4A/T4B/T4C)
• Controls: Peak Reduction, Output Gain, HF Emphasis (sidechain)
• Frequency response: 15 Hz - 20 kHz (+/- 1 dB)
• Maximum gain: +40 dB
• Maximum peak reduction: -40 dB
• THD: <0.1% at +10 dBm
• Noise: -74 dB
• Attack: 10 ms
• Release: 0.06 s (50%), 0.5 - 5 s (complete)
• Input/Output: 600 Ohm balanced (XLR and TRS)
• Stereo link: TRS (connects two WA-2A units)
• Power: 115/230V switchable, IEC
• Fuse: 1x 250V, 1A fast-blow
• Rack size: 2U, 19"
• Dimensions: 483 x 178 x 89 mm (19 x 7 x 3.5")
• Weight: 5.4 kg (12 lbs)

In the Box

• Warm Audio WA-2A
• IEC power cable