T L Audio User Manual Ebony Series A2 Stereo Processor TL Audio Limited, Letchworth, England. Tel 01462 492090, Fax 01462 492097. www.tlaudio.co.uk email: info@tlaudio.co.uk TABLE OF CONTENTS TABLE OF CONTENTS.............................................................................................................................. 1 INTRODUCTION ......................................................................................................................................... 2 WHY CLASS-A?............................................................................................................................................ 2 WHY TUBES?................................................................................................................................................ 3 WHY BALANCED I/O?.................................................................................................................................. 3 THE A2 STEREO PROCESSOR. ...................................................................................................................... 4 PRECAUTIONS ............................................................................................................................................ 5 BLOCK DIAGRAM...................................................................................................................................... 6 INSTALLATION........................................................................................................................................... 7 AC Mains Supply. .................................................................................................................................... 7 Audio Inputs............................................................................................................................................. 7 Outputs. .................................................................................................................................................... 8 Ventilation................................................................................................................................................ 8 OPERATION. ................................................................................................................................................ 9 Input Gain stage ...................................................................................................................................... 9 Tube Stage Drive and Peak LEDs.......................................................................................................... 9 WHAT IS COMPRESSION? ............................................................................................................................. 9 Overview of Compressor Operation. ................................................................................................... 10 Threshold. .............................................................................................................................................. 10 Attack and Release. ............................................................................................................................... 11 Gain Make Up. ...................................................................................................................................... 11 Compressor On...................................................................................................................................... 12 Equalisation. .......................................................................................................................................... 12 LF Band.................................................................................................................................................. 12 Mid Band................................................................................................................................................ 12 HF Band................................................................................................................................................. 12 EQ On..................................................................................................................................................... 13 EQ Pre.................................................................................................................................................... 13 EQ Side Chain ....................................................................................................................................... 13 Sidechain Operation.............................................................................................................................. 13 Output Gain. .......................................................................................................................................... 13 Digital Output........................................................................................................................................ 14 Output Peak LED. ................................................................................................................................. 14 GETTING STARTED ................................................................................................................................ 14 Using as an inserted dynamic effect..................................................................................................... 15 Using to process your stereo mix / mastering ..................................................................................... 15 SPECIFICATIONS ..................................................................................................................................... 18 Line Inputs: ............................................................................................................................................ 18 Outputs:.................................................................................................................................................. 18 Tube Stage: ............................................................................................................................................ 18 Compressor: .......................................................................................................................................... 18 Equaliser:............................................................................................................................................... 19 Metering:................................................................................................................................................ 19 Power Requirements: ............................................................................................................................ 19 Dimensions: ........................................................................................................................................... 19 SERVICE ...................................................................................................................................................... 20 1 INTRODUCTION New from TL Audio, The Ebony Series is a sleek looking range of discrete Class A processors designed to heighten your audio experience. The range consists of 3 units, all of which use Discrete Class A circuitry and have an optional tube stage with variable drive putting you in control of how `creamy' or how `cool' your unit sounds. Hand assembled in England to the highest standards, the Ebony uses stylish, quality chrome knobs together with a high gloss black finish to make the exterior look just as smooth as the circuits sound. The Ebony Series have all the features you come to expect with TL Audio, including balanced I/O, multi input options, analogue VU metering and intuitive, precise controls. All units are also compatible with the TL Audio DO-2 digital SPDIF interface for easy digital connectivity with high quality conversion. A combination of supreme quality, unrivalled sound and stylish aesthetics - this range offers superior analogue processing to accompany a digital world. Why Class-A? Class A circuits are designed with a constant current flowing through all of the transistors, which is sufficient to drive the peak output required from each block of the circuit. This ensures that every transistor is kept at its optimum operating point, minimising non-linearities due to changes in current and internal thermal effects, and eliminating the objectionable "cross-over" distortion typical of class AB circuits. Due to the higher steady state (or "quiescent") currents used, the power dissipation of class A circuits is substantially higher than can in general be handled by integrated circuits. It is also possible to design discrete transistor circuits to operate at higher voltage rails than are available for audio integrated circuits, adding the benefit of greater headroom and improved dynamic range. For these reasons, there are no integrated circuits in the audio paths of the Ebony Series. The outstanding audio quality is reflected in the technical specification of the units, with particularly low noise and distortion, and wide frequency response. 2 Why Tubes? Valves - or "Tubes" - have long been associated with excellent audio quality, recognised as adding "warmth" or "depth" to a signal. Driving the valves harder results in an increasing level of mainly second harmonic distortion, which is responsible for the characteristic overdriven valve sound. The Ebony Series feature variable drive valve circuits, which may be switched into the audio paths, or bypassed completely. The valve drive control varies the signal level through the valve stage, without affecting the overall gain from input to output. It is therefore possible to vary to the degree of harmonics added by the valve, from subtle warming to crunchy overdrive, with a single control. The signal level through the valve is displayed by the variable intensity "Drive" LED and the "Peak" LED. Where instrument inputs are present on the Ebony models, dedicated valve input stages are used. Switchable to high or low sensititivity (and impedance), these input stages represent the ultimate quality for the first stage of instrument amplification. Why Balanced I/O? Balanced I/O (Inputs and Outputs) are always preferable to unbalanced connection in an audio system. A balanced signal consists of signal phase and non-phase connections, which form a differential pair, independent of the ground (or earth) connection. Noise, particularly mains hum and high frequency interference, can often be present in unbalanced systems due to small differences in ground potential or circulating ground currents ("loops") between units, where the signal phase (only) is taken as an absolute value with respect to ground. A correctly designed balanced interface should have both phase and non-phase signals of equal magnitude (and source impedance), but should allow either of the phase and non-phase signals to be connected to an arbitrary electrical point (e.g. ground) without changing the differential level. Therefore, if, for instance, the non-phase signal is shorted to ground by an unbalanced input on a piece of equipment, then the phase signal should double in magnitude to compensate. Such an arrangement is referred to as "floating" or "ground-free". Balanced signals require 3 pin connectors, such as XLR's or TRS jack plugs, carrying the phase and non-phase signals, plus a screening ground connection. Naturally, the Ebony Series features balanced, ground-free signals for all line inputs and outputs, as well as insertion points where present. The range is also compatible with unbalanced equipment, as described above. 3 The A2 Stereo Processor. The Ebony Series A2 Processor is a dedicated stereo unit, providing gain and phase control, compression and equalisation. A tube stage is available to each signal path, with variable drive control. The block diagram of the unit is shown in fig.1. The tube stage has a variable drive control, with the signal level indicated by the variable intensity "Drive" LED and "Peak" LED. Use of this feature typically introduces 1% to 10% harmonic distortion, predominately second harmonic, without changing the output level from the unit. The tube stage can be selected or bypassed as required. The Compressor has continuously variable threshold, ratio and gain make-up, and switched settings for hard or soft knee and fast or slow attack and release times. The compressor is stereo coupled, to ensure both A and B channels are compressed identically, in order to preserve the stereo image. The Equaliser has 3 bands. The HF and LF controls are shelving whilst the mid control is a swept, peaking filter. The equaliser is fully discrete class A. Comprehensive switching (via relays) allows the A2 to be configured with th ...