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Tube Tech LCA 2B Stereo Tube VCA Compressor / Limiter

Tube Tech LCA 2B front view

The Tube Tech LCA 2B is a dual channel all tube VCA Compressor and Limiter. The LCA 2B is a Vari Mu compressor that uses the tube as the VCA.

The TUBE-TECH LCA 2B is a two-channel unit with an independent compressor and limiter per channel. The LCA 2B is all tube based (except for the power supply and side chain circuit). The VCA (1 dual triode) is placed between the input transformer and the output stage (2 dual triodes).

The LCA 2B is one of the most powerful and versatile VCA compressors in the market: LCA 2B is extremely versatile, and it works equally well on vocals, instruments and as a bus compressor. Due to its very fast and smooth attack it is also perfect for drums and percussion.

There’s literally nothing this compressor can’t handle very well: Powerful bus compression (it’s a dream used for bus compression both inserted and in parallel.) and fine single instrument and voice compression. The action of the LCA2B is always easy to hear, so finding the right setting on this compressor is a not complicated.

LCA2B is designed to be the TUBE-TECH equivalent of the Fairchild 670, but only in terms of action, not the actual electronics. It is designed with the Fairchild in mind, delivering similar action but retaining its transparency or high frequencies, even when pushed to the limit). The fixed attack/release constants are duplicates of the Fairchild constants.

The audio signal is picked up after the VCA and fed to the side chain circuit. The control signal from the compressor and from the limiter is combined and sent to the link switch and to the control amp, which feeds the VCA. The two bi-directional link busses are accessible at two 1/4" stereo jack sockets on the rear panel. The channels can be linked together for stereo applications and also linked to other LCA 2B's via the two link busses and a standard stereo jack/jack cord.

The compressor has six att/rel presets as well as manual control. The limiter att/rel is fixed. The LED display is fed from the con-trol amp. The limiter LED is fed from the limiter buffer.The audio path is fully symmetrical from input to output. Input and output have fully floating transformers. All DC voltages are stabilized, ex-cept the anode voltage for the output stage.

LCA 2B Features

General

  • Tube VCA compressor/limiter
  • All-tube based push-pull amplifier
  • Frequency response @ -3 dB: 5 Hz to 50 kHz
  • Low noise: < -85 dBU @ 10 dB gain
  • CMRR: > 60 dB @ 10 kHz
  • Separate compressor and limiter
  • Output Gain: -6 dB to +10 dB
  • Interconnection of several compressors via two busses
  • Clickless In/Out relay
  • Conductive plastic potentiometers
  • Gold plated switches
  • Inputs and outputs are transformer balanced and fully floating
  • Linkable for stereo applications

Compressor

  • Variable ratio (1.6:1 to 20:1)
  • Variable threshold (Off to -20 dBU)
  • Continuously variable attack and release times
  • Choice between 6 presets (Fairchild) and manual attack/release control
  • LED Gain reduction display

Limiter

  • Variable threshold (Off to 0 dBU)
  • Attack: 0.8 ms – release: 0.5 sec
  • Separate Limiter On/Off switch
  • LED indication of limiter action

Looking after the LCA 2B

Like any other VCA tube compressor the LCA 2B occasionaly needs calibration.

It is recommended that the unit should be calibrated at least once a year even though in real life, depending on the ECC81 compression tube, the LCA 2B will work for a longer period of time.

A quick test to tell if calbration is needed.

  • Turn the THRESHOLD for both compressor and limiter fully CCW.
  • Connect a 1kHz tone at a level of 0 dBU (-4VU) to the input and turn the LIMITER THRESHOLD
    slowly CW until the LIM led (RED) turns slightly on.
  • If the LIM led (RED) turns on abruptly or even starts oscillating, the balance should be calibrated.

This test can also be done with audio: If the LCA2B needs calibration, the compressor starts pumping with this extreme setting.

Our in-house service department calibrates tube VCA compressors so if you have a unit that needs calibrating please book the unit in through our online form.

Tube Tech LCA 2B Specifications

Impedance

  • Input: > 5 kohm
  • Output: < 60 ohm

Frequency response @ -3 dB: 5 Hz to 50 kHz

Distortion THD+N @ 40 Hz

  • 0 dBu: < 0,15 %
  • +10 dBu: < 0,15 %


Noise Rg=200 ohm

  • Output Gain @ 0dB +10 dB
  • 22 Hz-22 kHz: < -85 dBu < -80 dBu
  • CCIR-468-4: < -78 dBu < -73 dBu

Cross talk @ 10 kHz: < -70 dB

  • CMRR @ 10 kHz: < -60 dB
  • Max. output @ 1 % THD+N: > +26 dBu
  • Gain -6 dB to +10 dB

    Compressor

    • Ratio: 1,6:1 to 20:1
    • Threshold: off to -10 dBu
    • Attack: 0,3 ms to 70 ms
    • Release: 0,07 ms to 2 s

    Limiter

    • Ratio: 20:1
    • Threshold: off to 0 dBu
    • Attack: 0,8 ms
    • Release: 0,5 s

    Tubes

    • ECC 81 2 pc
    • ECC 82 2 pc
    • ECC 83 2 pc

    Dimensions

    • Height:2 units 88 mm 3,5"
    • Width: 480 mm 19,0"
    • Depth: 205 mm 8,1"

    Weight

    • Net: 6,5 kg 14,3 lbs.

    Power requirements

    • @ 115 V/230 V, 50-60 Hz: 30-45 W
  • Exploring the Tube Tech LCA 2B