Alice 538T - 500-Series Stereo OPTO Compressor with Transformers

Alice 538T - 500-Series Stereo OPTO Compressor with Transformers

The Alice 538T is a stereo 500 series Optical compressor. This unique design is a feed forward design, and also features a width control meaning more creative effects can be achieved with this compressor that other analogue designs.  

The ‘538T’ is designed for creative compression effects that are difficult to achieve with plug-ins. It’s capable of extreme compression just as Ted’s original Joe Meek SC2 V5; amazing drum sounds! It’s also super-quality ‘Levelling Amplifier’ with the sparkle of a well-designed opto compressor

Mechanical

The 538T occupies two spaces in a standard API 500 series rack using normal ins and outs for left and right

Inputs & Outputs

Left and Right balanced or unbalanced inputs

Left and Right balanced outputs via hand matched OEP Z3001C canned transformers

Width Control

In order to retain perfect symmetry between the left and right channels of the stereo equaliser the audio signal is processed into ‘sum and difference’ mode (that is L+R = ‘sum’, L-R = ’difference’), the two audio signals are then processed by the EQ controls before being re-processed back into left and right format. By going through this process the left and right channels remain perfectly symmetrical with no image shift, any minor difference between the processed sum and difference signals show up only as small deviations in width of the stereo image. A further useful advantage of the sum and difference processing is that the width of the stereo image is controlled by the volume level of the ‘difference’ channel so by adding a gain control the stereo width can be accurately controlled. With the width control at minimum the audio output is mono. When the control is half way, the processing accurately recombines the audio into left and right. If the control is increased further, the image is extended beyond the original stereo.

Metering

Easy-to-read analogue meter reading audio (UV) or compression depth (comp)

Specifications

• Inputs: 10K impedance differential balanced.
• Outputs: Floating balanced 50 ohm. Max balanced output approx. +26dBu
• Gain: Maximum 24dB
• Noise: At least 80dB below operating level Dynamic range exceeds 100dB.
• Harmonic Distortion: Generally within 0.005%. 2nd order harmonic distortion rises at lower frequencies under compression.
• Amplitude Frequency response: Line in 20Hz to 20KHz within 1dB.
• Audio Crosstalk: the 538 uses M/S processing (sum and difference) with ‘side’ content variable via the width control. With width set at 100% L/R crosstalk can be better than -50dB.
• Compressor: Photoresistive servo operated feedback type· Ratio non-linear; minimum approx. 1.2 to 1 maximum approx. 8 to 1. Sidechain filtered for correct bass compression.Attack time 1mS min. 10mS max. (variable) Release time 200mS min 1.5S max. (variable)
• Connections: via 2 X 500 series sockets.
• Power: 3 Watts. Powered from 500 series rack. +ve rail 68mA, -ve rail 106mA.
• Housing: 2 spaces of 500 series rack.