The PA-1 from TL Audio is a dual channel, tube based microphone and instrument amplifier. Transformer coupled microphone inputs and front panel instrument inputs are amplified by pentode and triode tube stages with variable gain and switchable high- and low-frequency filters. The output levels are controlled by rotary faders with headroom indicated by signal, peak and clip LEDs.
The microphone input is balanced, suitable for low impedance (150 to 600Ω) microphones and is transformer coupled to the EF86 pentode first stage tube. A twin ECC83/12AX7 triode provides second stage gain plus variable trim built around the third stage. The instrument input bypasses 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 high- and low-frequency filters cut stages are second order passive filters which are switchable to Off (i.e. maximum bandwidth,) plus three 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.