TL Audio A4 User Manual

T L Audio

User Manual

Ebony Series A4 Summer

TL Audio Limited, Letchworth, England.

Tel [phone], Fax [phone].

www.tlaudio.co.uk email: [e-mail]

2

CONTENTS.

CONTENTS. ...................................................................................................................................................2

INTRODUCTION..........................................................................................................................................3

WHY CLASS-A? ............................................................................................................................................4

WHY TUBES? ................................................................................................................................................4

WHY BALANCED I/O? ..................................................................................................................................4

PRECAUTIONS.............................................................................................................................................6

BLOCK DIAGRAM ......................................................................................................................................7

INSTALLATION ...........................................................................................................................................8

AC Mains Supply......................................................................................................................................8

Inputs. .......................................................................................................................................................8

Insertion Points. .......................................................................................................................................9

Balanced XLR Outputs. .........................................................................................................................10

Level Selection. ......................................................................................................................................10

Ventilation. .............................................................................................................................................10

OPERATION................................................................................................................................................11

Input Gain stage.....................................................................................................................................11

Channel Pan Control .............................................................................................................................11

Input switching .......................................................................................................................................11

Tube Stage Drive and Peak LEDs. .......................................................................................................11

Tube Drive Control ................................................................................................................................11

Insertion Points ......................................................................................................................................12

Output Gain............................................................................................................................................12

Metering .................................................................................................................................................12

SPECIFICATIONS......................................................................................................................................13

Power Requirements:.............................................................................................................................14

SERVICE.......................................................................................................................................................15

3

INTRODUCTION

Thank you for purchasing the Ebony A4 Summer. 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. A combination of supreme quality, unrivalled
sound and stylish aesthetics - this range offers superior analogue processing to
accompany a digital world.

The Ebony Series A4 Summer is a 16 channel unit, accepting balanced or unbalanced
line inputs, switchable between +4 and -10dB, via TRS Jack or DSUB connector.
Each channel has individual Pan control, and there is also master gain control and
balanced insert points with bypass. A tube stage may be switched into the master
signal path, with variable drive control.

The block diagram of the processor is shown in fig.1. A discrete Class A electronically
balanced input is used, delivering superior audio performance with very low noise,
and wide bandwidth

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. This even harmonic distortion gives the colour
and sound that tubes are famed for. The tube stage can be selected or bypassed as
required.

A VU meter is provided, which can be selected to either 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). In the +10 mode, 0VU is
calibrated as +14dBu out.

4

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 so that they enjoy this
improved dynamic range and greater headroom.

The outstanding audio quality is reflected in the technical specification of the units,
with particularly low noise and distortion, and wide frequency response.

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.

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.

5

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.

Please read this manual fully before installing or operating the Processor.