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),
Loading...