T L Audio User Manual Ebony Series A3 Mono Processor TL Audio Limited, Letchworth, England. Tel 01462 492090, Fax 01462 492097. www.tlaudio.co.uk email: info@tlaudio.co.uk CONTENTS INTRODUCTION ......................................................................................................................................... 3 WHY CLASS-A?............................................................................................................................................ 4 WHY TUBES?................................................................................................................................................ 4 WHY BALANCED I/O?.................................................................................................................................. 5 BLOCK DIAGRAM...................................................................................................................................... 6 PRECAUTIONS ............................................................................................................................................ 7 INSTALLATION........................................................................................................................................... 8 AC Mains Supply. .................................................................................................................................... 8 Mic Input.................................................................................................................................................. 8 Line Input. ................................................................................................................................................ 9 Instrument Inputs..................................................................................................................................... 9 Insertion Point. ........................................................................................................................................ 9 Output..................................................................................................................................................... 10 Ventilation.............................................................................................................................................. 10 OPERATION ............................................................................................................................................... 11 Input Stage. ............................................................................................................................................ 11 Microphone Input. ................................................................................................................................. 11 Line Input. .............................................................................................................................................. 11 Instrument Input. ................................................................................................................................... 11 30dB Pad................................................................................................................................................ 12 90Hz Filter............................................................................................................................................. 12 Phantom Power. .................................................................................................................................... 12 Tube Stage Drive and Peak LEDs........................................................................................................ 12 WHAT IS COMPRESSION? ........................................................................................................................... 12 Overview of Compressor Operation. ................................................................................................... 13 Threshold. .............................................................................................................................................. 13 Attack and Release. ............................................................................................................................... 14 Gain Make Up. ...................................................................................................................................... 15 Compressor On...................................................................................................................................... 15 Equalisation. .......................................................................................................................................... 15 LF Band.................................................................................................................................................. 16 Mid Band................................................................................................................................................ 16 HF Band................................................................................................................................................. 16 EQ On..................................................................................................................................................... 16 EQ Pre.................................................................................................................................................... 16 Output Gain. .......................................................................................................................................... 16 Digital Output........................................................................................................................................ 17 Output Peak LED. ................................................................................................................................. 17 GETTING STARTED ................................................................................................................................ 18 CONNECTIONS. ........................................................................................................................................... 18 IN USE......................................................................................................................................................... 19 SPECIFICATION ....................................................................................................................................... 21 Mic Input:............................................................................................................................................... 21 Line Input:.............................................................................................................................................. 21 Instrument Input: ................................................................................................................................... 21 High Pass Filter: ................................................................................................................................... 21 Insertion Point:...................................................................................................................................... 22 Output: ................................................................................................................................................... 22 Tube Stage: ............................................................................................................................................ 22 Compressor: .......................................................................................................................................... 22 Equaliser:............................................................................................................................................... 22 1 Metering:................................................................................................................................................ 23 Power Requirements: ............................................................................................................................ 23 Dimensions: ........................................................................................................................................... 23 SERVICE ...................................................................................................................................................... 24 2 INTRODUCTION The TL Audio Ebony Series of audio processors are a sleek looking range of discrete Class A processors designed to heighten your audio experience; they use signal paths constructed from discrete transistor "Class A" circuits, with switchable variable drive tube stages, putting you in control of how `creamy' or how `cool' your unit sounds. These techniques provide very high quality, uncoloured audio, with the option to add valve warmth at the touch of a button. 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. The Ebony Series A3 Processor is a single channel unit, accepting mic, line and instrument inputs. Processing includes gain and phase control, compression and equalisation. A tube stage may be switched into the signal path, with variable drive control. The block diagram of the processor is shown in fig.1. A discrete Class A electronically balanced mic input amplifier is used, delivering superior audio performance with very low noise, low distortion and wide bandwidth. The mic input is suitable for low impedance (150-600 ohm) microphones, with a gain control range of +16 to +60dB. Front panel switches provide 48V phantom power, and 30dB pad for high output mic applications. The front panel mounted jack socket is suitable for a variety of sources, including electric guitar, acoustic pickup and keyboard. The instrument input has high/low switching, and a dedicated valve input stage. Phase reverse and high pass filter switches are provided; affecting whichever of the mic, line and instrument inputs are selected. 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. 3 The Equaliser has 3 bands. The HF and LF controls are shelving whilst the mid control is a swept, peaking filter. Comprehensive switching (via relays) allows the A3 to be configured with the equaliser pre or post the compressor, or with the equaliser in the sidechain, for deessing or frequency variable compressor effects. A VU meter is provided, which can be selected to either input or output signals. It may also be selected to display the compressor Gain Reduction. In this mode the meter normally indicates 0dB, falling back as the signal is compressed. The amount of compression may be read directly from the dB scale. The meter is also provided with a "+10dB" switch, which keeps the reading on the scale when driving a high level out (to a DAW, for example). In the +10 mode, 0VU is calibrated as +14dBu out. 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. Fo ...