TL Audio A1 - Manual (Page 4)

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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.
Where instrument inputs are present on the Ebony models, dedicated valve input
stages are used. Switchable to high or low sensititivity (and impedance), these input
stages represent the ultimate quality for the first stage of instrument amplification.
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.
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.
The A1 Dual Pre-Amp.
The Ebony Series A1 Pre-Amp features two independent channels, with each channel
offering mic and instrument inputs.