INTRODUCTION
The T L Audio Indigo Series combines classic valve techniques with low noise solid
state circuitry to produce audio processing units offering very high quality signal paths
with comprehensive control facilities and the unique valve sound.
The EQ-2011 is a two channel valve equaliser. Four bands of EQ are provided on each
channel, each with a switched frequency selection to cover the full audio bandwidth.
The block diagram of one channel of the unit is shown in fig.1. It has three input
sources - a balanced line level input via an XLR connector, an unbalanced line level
input via a jack socket, and an instrument input also on an unbalanced jack socket but
located on the front panel where it provides a convenient means of patching a guitar or
keyboard directly into the equaliser. All three inputs may be used simultaneously. The
gain of the input stages is controlled by a centre-detented control, calibrated for 0dB
nominal gain from the line input sources at the centre and pro/-20dB of
variation. The instrument input has a sensitivity switch associated with it, to match the
gain to a low level pickup (e.g. a passive guitar or microphone) or a higher output
source such as a keyboard or active guitar, followed by the 40dB variation of the input
gain control.
After the input stage, the signal is fed to the four valve stages, which are arranged as a
pre-amplifier stage, a combined LF/HF shelving stage and two separate peaking mid
bands. The valve equaliser stages use the established TL Audio circuitry which offers
a wide dynamic range and frequency response, low noise, low distortion and broad
control range.
A variable intensity peak LED monitors the output of the valve stages, providing an
indication of the amount of drive and headroom available.
The signal chain is completed by an EQ-in switch plus balanced and unbalanced
output driver stages.
Please read this manual fully before installing or operating the Equaliser.
