User manual TL AUDIO A3

[. . . ] 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?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [. . . ] Start with the input gain control set to minimum, and the output master at the mid-point (12 o'clock position). The input gain can then be gradually increased until the VU meter registers about 0VU on normal signal level, when set to read `IN'. The master output level should then be adjusted to produce the required output. CAUTION: Never switch phantom power on or off, or plug/unplug a microphone with phantom power applied unless the output level controls turned down. Failure to do so may result in a thump in your monitor loudspeakers or PA system. Line Input. A line level signal should already be at about the correct operating level, but monitoring the level on the output meter, with the compressor bypassed and the output gain at 0dB, could check this. The input gain should be adjusted until the meter reads about 0VU at normal audio level, when set to read `IN'. Instrument Input. The front panel instrument input socket is suitable for low level sources such as hi impedance microphones, pick ups or passive guitars, and higher level sources such as active guitars and keyboards, as it is switchable to high or low sensitivity. 11 30dB Pad. Occasionally ­ when using sensitive condenser microphones ­ the source signal may be too loud for the input preamp. In this situation, to avoid any overloading or distortion of the mic preamp stage, the 30dB pad can be used to reduce the input gain to a more manageable level. The 30dB pad only applies to the microphone input. 90Hz Filter. The high pass filter switch restricts the low frequency response of the preamp, to effectively remove rumble of LF noise from the signal. The filter can be useful in restricting `popping' on vocals or even low frequencies caused by contact with microphone stands or microphone cables. Popping is an undesirable thump that is caused by close-miking certain spoken or sung letters, namely "P" or "B". These particular letters cause a sudden expulsion of air that can result in an audible thump. As this thump has a lot of low frequency content the high pass filter can help to reduce the problem, as can using a pop filter (a device usually made out of nylon material similar to stockings) suspended in front of the microphone. The 90Hz filter is active on the mic, line and instrument inputs. Phantom Power. +48V phantom power is available at the mic socket, selected by a front switch. Phantom power should only be used in conjunction with suitable microphones. CAUTION: Operation of the phantom power switch, or plugging a microphone in or out with phantom power applied, may cause a click or thump in your loudspeakers. To prevent this happening, ensure that the system gain is set to minimum (e. g. on your mixing console fader or power amplifier), before operating the switch or plugging in a microphone. Tube Stage Drive and Peak LEDs. These LEDs indicate the drive level to the tube, or valve, stage. The Drive LED is a variable intensity indicator, starting to glow when the tube harmonic distortion is around 1%, and being fully illuminated at approximately 5% harmonic distortion. The distortion is predominately second harmonic, unless very high drive levels are used, in which case the tube is eventually pushed into harsher saturation, indicated by the tube Peak LED. What is Compression? Compression is an essential but often misunderstood process in modern recording. Put simply, compression reduces the difference between the loudest and the quietest levels 12 of an audio signal. This is known as reducing the "dynamic range" of that signal and is a powerful tool for an engineer helping to avoid overloading, distortion problems as well as raising the level of the quieter parts of the audio signal. Before the introduction of compressors the only way this could be achieved was by "gain riding", whereby an engineer would control the fader manually in order to try and anticipate very large levels (which might distort the signal) or very low levels (which may get lost in noise). [. . . ] You should also notice that increasing the Ratio setting causes more gain reduction to occur. When gain reduction is taking place, you should notice that the output level is reduced. By switching the compressor `in' and `out', you can compare the levels and the subjective sound quality of the original and compressed signals. With the compressor active, use the Gain Make- Up control to set the level so that when disabling the compressor, there is no level drop. [. . . ]