T L Audio
User Manual
PA1 PENTODE PRE-AMPLIFIER
Tony Larking Professional Sales Limited,
Letchworth, England.
Tel: 01462 490600. International +44 1462 490600
INTRODUCTION
The T L Audio Dual Pentode Pre-Amplifier is a very high quality, valve based microphone and instrument amplifier. Transformer coupled microphone inputs and front panel accessible instrument inputs are amplified by Pentode and Triode valve stages with variable gain and switchable HF and LF filters. The output levels are controlled by rotary faders, with headroom indicated by Signal, Peak and Clip LEDs.
The block diagram of one of the channels is shown in fig.1. The microphone input is balanced, suitable for low impedance (150-600 ohm) microphones and is transformer coupled to the pentode first stage valve. The pentode valve type is the EF86, which has been employed in many of the renown valve amplifier designs from the 1960’s onwards, and which remains the first choice for a very low noise, high quality input stage. A twin ECC83/12AX7 triode provides second stage gain plus variable trim built around the third stage. The instrument input is via an unbalanced jack socket on the front panel, bypassing the transformer, and is suitable for medium to high impedance sources including active and passive guitars, and keyboards.
Gain control is switched in 10dB increments, from 20dB to 50dB, with the continuously variable, centre-detented, trim control adding a further +/- 12dB. The HF and LF Cut stages are second order passive filters which are switchable to Off (i.e. maximum bandwidth), plus 3 frequencies per filter. Channel A is additionally equipped with a phase reverse switch to ensure correct phase relation of an overall stereo system.
A solid state, balanced output stage completes the signal path by providing a high drive capability suitable for connection to virtually any mixing console, amplifier or PA system. An unbalanced jack socket output and +4dBu / -10dBu nominal output level switch are also provided.
Please read this manual fully before installing or operating the Pentode Pre-Amplifier.
PRECAUTIONS
The T L Audio Pentode Pre-Amplifier requires very electrical equipment, care must be taken to ensure following points should always be observed:
little installation, but like all reliable, safe operation. The
-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 the 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
The rear panel connectors are identified in fig.2.
AC Mains Supply.
The Pre-Amplifier is fitted with an internationally approved 3 pin IEC connector. A mating socket with power cord is provided with the unit, wired as follows:
Brown: Live.
Blue: Neutral.
Green/Yellow: Earth (Ground).
All mains wiring should be performed by a qualified electrician with all power switched off, and the earth connection must be used.
Before connecting the unit to the supply, check that the voltage selector switch on the rear panel is correctly set. 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 fuse required is 20mm anti-surge, 1AT.
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