INTRODUCTION
The T L Audio EQ2 Parametric Valve Equaliser combines classic valve techniques
with low noise solid state circuitry to produce a unit offering sweepable high and low
pass filters plus four bands of fully variable equalisation on each of its two channels.
Both channels feature a line level input, plus a mic input with switchable 48V
phantom powering. Further flexibility is provided from a front panel auxiliary input
and stereo operation mode. Typical applications include direct recording to tape,
instrument preamplifier, use as outboard EQ during mixdown, and as a main stereo
equaliser for monitoring and PA systems.
The block diagram of one of the channels is shown in fig.1. A solid state,
electronically balanced input amplifier is used, to achieve state of the art performance
with very low noise, low distortion and wide bandwidth. Two XLR input sockets are
provided per channel, for mic and line inputs. The mic input is suitable for low
impedance (150-600 ohm) microphones, with a gain control range of +16 to +60dB. A
front panel switch provides 48V phantom power to both channels. The line input has
an effective overall gain range of -10 to +35dB, allowing the valve stages to be fully
driven from line level signals in the range -20 to +20dBu.
A front panel mounted auxiliary jack socket allows direct access to the channel inputs.
The input is suitable for a variety of sources, including guitar, acoustic pickup and
keyboard.
The input section also provides continuously variable, individually switchable, high
and low pass filters to tailor the frequency response to eliminate unwanted LF or HF
noise from the input source.
An insertion point is provided immediately after the input stage, to allow a compressor
or other processor to be used as required. The insertion point is unbalanced, at a
nominal operating level of -2dBu.
Both channels feature a four band parametric equaliser. Each band is individually
switched in or out of circuit, and an overall EQ in switch is provided. All of the EQ
bands comprise centre-detented cut or boost control, swept frequency and
continuously variable Q controls. A total of six twin triode valves are employed in the
EQ2: one valve stage per EQ band, plus a two stage post EQ driver circuit.
Master level controls are provided, post EQ. These controls are also centre-detented
for ease of line-up, but may be varied in conjunction with the input gain controls to
alter the operating level through the valve circuitry, to introduce as much (or as little)
of the characteristic valve sound as required. Variable intensity peak LEDs glow to
indicate the degree of valve drive attained.
