TL Audio 5021 - Manual (Page 13)

4.4 Input
Stage.
The Input Gain control sets the level of the line or instrument signal into the
5021. Both the line input and the instrument input remain active
simultaneously, therefore it is recommended to disconnect any inappropriate
connection when not in use to minimise noise. The instrument input allows
high impedance instruments such as guitars or a bass etc to connect directly
into the 5021 and eliminates the need for a DI (Direct Injection) Box. A wide
range of signals can be fed into the 5021, and the Input Gain control also
allows the valve stages to be driven to a variable degree. After the preamp
stage the signal passes through a triode valve stage positioned between the
input circuit and the compression section. Increasing the input gain pushes
more signal level into the valve, thus generating more harmonic distortion and
creating that special “valve sound”. This is indicated by the yellow drive led
that will glow more intensely as the level increases. At the same time the
output level can be turned down to preserve the same level at the outputs, so
a choice of sounds is available. For a more pronounced valve sound, turn up
the input gain and reduce the output gain, and vice versa for a cleaner sound.
Don’t be afraid to push the 5021 hard!
As well as driving the valves harder, increasing the Input Gain control setting
will also have a pronounced effect on the amount of compression, as the
threshold will remain constant as the input level increases. If the input gain is
adjusted, the threshold can be altered accordingly to maintain a similar
amount of compression.
4.5
Drive and Peak LEDs.
The yellow Drive LED provides a visual indication of the signal level through
the valve stages, and therefore the extent of “warming” or valve character
being introduced. The drive LED will gradually illuminate as the input level or
gain is increased, over the range 0dB to +12dB.
The red Peak LED operates as a conventional warning that clipping is about to
occur. The operating level of the entire signal chain is monitored, and the LED
illuminates when there is less than 5dB of headroom remaining. Normal
operation would be to set the input gain so that the drive LED is regularly
illuminating, with occasional lighting of the red Peak LED on transients.
If the input and output gain controls are set to their centre (0dB) positions, the
Peak LED will illuminate some 8dB after the Drive LED has reached its full
intensity. However, it is possible to add gain further down the chain (i.e. output
level gain), which will cause the Peak LED to illuminate at a lower level of
Drive. This situation implies that a high level of “clean” signal is present,
without driving the valves hard.