Union Tube & Transistor LAB - Optical Compressor

Various

Union Tube & Transistor

The LAB is an optical compressor. It uses custom optocouplers to achieve up to 30dB of musical-sounding compression.

We loved how in the recording studio even with tons of compression the old optical compressors such as the LA-2A, the LA-3, the LA-4 sounded smooth and natural.

The essence of the LAB's sound comes from the fast attack and slow release times of the custom optocoupler. The optocoupler's behaviour is quite complex, and program-dependent. It can't be modelled with simple resistor-capacitor networks. We wanted the pure response of the optocoupler to define the LAB's dynamics, and not supplement that with RC filtering.

To that end, we tried out just about every off-the-shelf optocoupler on the market, but ended up designing and manufacturing our own custom units. There's an interplay between dynamics, noise floor, distortion, and available compression on the one hand, and the opto's electrical parameters on the other. Since nothing commercially available fit the bill, we built our own.

With just two controls – compression and gain make-up – the LAB is fast and simple to use. It sounds great on bass and electric guitar, and the noise floor is impressive – quiet enough for studio use. It really shines on acoustic guitar, vocals and drums.

LAB Optical Compressor Specifications

  • Power Requirements +9VDC @40mA
  • Input Impedance 1MΩ
  • Output Impedance 100Ω
  • Frequency Response 20Hz–20KHz ±0.1dB
  • Maximum Input Level +7.5dBu
  • Maximum Output Level +10.0dBu
  • Compression/Gain-makeup 30dB
  • Noise Figure (Rs=10K) 3dB

For studio use you will need to attenuate going in and boost coming out of the LAB.

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