TL Audio A4 - Manual (Page 4)

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.