User manual TL AUDIO A1

[. . . ] T L Audio User Manual Ebony Series A1 Dual Pre-Amp TL Audio Limited, Letchworth, England. www. tlaudio. co. uk email: info@tlaudio. co. uk TABLE OF CONTENTS TABLE OF CONTENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 WHY CLASS-A?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [. . . ] 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. 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. The A1 Dual Pre-Amp. The Ebony Series A1 Pre-Amp features two independent channels, with each channel offering mic and instrument inputs. 3 The block diagram of one of the channels 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 provides 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 both mic and instrument inputs. 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. A VU meter is provided, which can be selected to either channel, and input or output signals. 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). Please read this manual fully before installing or operating the Pre-Amp. 4 PRECAUTIONS The T L Audio Ebony Series units require very little installation, but like all electrical equipment, care must be taken to ensure reliable, safe operation. The following points should always be observed: - All mains wiring should be installed and checked by a qualified electrician, - Ensure the mains operating voltage stated on the rear panel is correct before connecting to the mains supply, - Never operate the unit with any cover removed, - Do not expose to rain or moisture, as this may present an electric shock hazard, - Replace the fuse with the correct type and rating only. Warning: This equipment must be earthed. 5 BLOCK DIAGRAM. 6 INSTALLATION AC Mains Supply. The unit is fitted with an internationally approved 3 pin IEC connector. All mains wiring should be performed by a qualified electrician with all power switched off, and the earth connection must be used. Please note that when using this unit with alternate supply voltages (in foreign countries, for example) the internal wiring of the unit may be set for 115V (accepting voltages in the range 110V to 120V, 60Hz AC) or to 230V (for voltages in the range 220V to 240V, 50Hz AC). [. . . ] Please beware not to let the signal ever clip (go into the red) on your DAW input (Logic, Pro Tools, Cubase etc). Clipping will cause digital distortion which a square wave and signal degradation. Experiment with the 90Hz filter - you should notice how it removes extreme LF content (particularly noticeable on close-miked male voices) and the 30dB pad will reduce the signal level quite markedly. The pad is only normally used on very loud sources where even minimum gain settings will drive the Ebony A1 preamp into distortion. [. . . ]