TL Audio EQ-2 User Manual
T L Audio
User Manual
EQ2 VALVE EQUALISER
Tony Larking Professional Sales Limited, Letchworth, England.
Tel 01462 490600, Fax 01462 490700.
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.
The Stereo mode switch is a powerful facility, enabling precise tracking of
equalisation between channels, with quick adjustment and no need to match settings
on two sets of controls. All of the EQ controls are ganged; i.e. Cut/Boost, Frequency,
Q and band in/out switching. The input and output gain controls, high and low pass
filters and overall EQ in/out switches retain individual channel operation for
maximum flexibility.
A solid state, electronically balanced output stage with outputs switchable for +4dBu
or -10dBu nominal output level completes the channel. The balanced signals are
terminated on metal XLR sockets, with unbalanced line level inputs and outputs
provided on 0.25” jack sockets.
Please read this manual fully before installing or operating the Equaliser.
PRECAUTIONS
The T L Audio EQ2 Parametric Valve Equaliser requires very little installation, but
like all electrical equipment, care must be taken to ensure reliable, safe operation. The
following points should always be observed:
- All mains wiring should be installed and checked by a qualified
electrician,
- Ensure the correct operating voltage is selected on the rear panel
before connecting to the mains supply,
- Never operate the unit with any cover removed,
- Do not expose to rain or moisture, as this may present an electric
shock hazard,
- Replace the fuse with the correct type and rating only.
Warning: This equipment must be earthed.
INSTALLATION
AC Mains Supply.
The equaliser is fitted with an internationally approved 3 pin IEC connector. A
mating socket with power cord and mains plug is supplied. All mains wiring should be
performed by a qualified electrician with all power switched off, and the earth
connection must be used.
Please note that when using this unit with alternate supply voltages (in foreign
countries, for example) the position of the voltage selector switch on the rear of the
unit may need adjusting. The unit may be set for 115V (accepting voltages in the
range 110V to 120V, 60Hz AC) or to 230V (for voltages in the range 220V to 240V,
50Hz AC). The setting may be adjusted by inserting a small flat bladed screwdriver
into the slot of the switch, and sliding the switch to the left (for 115V) or to the right
(for 230V).
Alternate supply voltages may also require a different power cable or mains plug. If in
doubt, consult local electrical regulations.
Warning: attempted operation on the wrong voltage setting, or with an
incorrect fuse, will invalidate the warranty.
Audio Inputs.
Each channel has two female, 3 pin XLR connectors, for mic and line sources. Both
are compatible with either balanced or unbalanced signals, when the mating
connectors are appropriately wired:
Balanced inputs:
- Pin 1 = Ground (screen).
- Pin 2 = Signal Phase (“+” or “hot”).
- Pin 3 = Signal Non-Phase (“-” or “cold”).
Unbalanced inputs:
- Pin 1 = Ground (screen)
- Pin 2 = Signal Phase (“+” or “hot”).
- Pin 3 = Signal Ground.
When using unbalanced signals, the signal ground may be obtained by linking pins 1
and 3 in the mating XLR connector. Good quality screened cable should be used,
particularly for microphone or low level sources, to prevent hum or noise pickup.
Unbalanced Line Inputs.
An unbalanced line level input is provided for each channel, on a 0.25” mono jack
socket. The mating plugs should be wired as follows:
- Tip = Signal Phase (“+” or “hot”).
- Screen = Ground.
Auxiliary Inputs.
A 2 pin (mono) jack plug is required, which should be wired as follows:
- Tip = Signal Phase (“+” or “hot”).
- Screen = Ground.
Insertion Points.
The insertion points are interfaced via a 3 pin, 0.25” switched jack socket on the rear
of the unit. The pin connections are:
- Sleeve = Ground,
- Tip = Send,
- Ring = Return.
The insertion point is unbalanced, and operates at a nominal level of -2dBu . If used
as an additional send only (e.g. as a send to a tape machine or monitor mixing desk),
the Tip and Ring should be wired together, to preserve the signal path through the
insertion point.
Outputs.
The outputs are via balanced, 3 pin male XLR connectors. The mating connectors
should be wired as follows:
- Pin 1 = Ground (screen),
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