Based on the MP 1A tube microphone preamp from Tube Tech, the PM 1A is a modular version that fits into their RM8 desktop power supply. The preamp also features a DI input and features extremely controlled and transparent sound.
The amplifier consists of a microphone input transformer with a step-up of +10dB, a dual tube preamplifier with 10dB/step coarse gain over a 20dB to 60dB range, augmented by a fine 2dB stepped attenuation of +/- 10dB, providing a total gain range of +10db to 70dB.
The output amplifier features 2 dual tubes in a push-pull configuration and an output transformer. The microphone input is provided with a switchable -20dB pad, selectable input impedance, switchable phase reverse and switchable +48V phantom power.
A Hi-Z direct inject input is unbalanced and placed in the circuit directly after the input transformer. The gain range for the DI input is 0dB to +60dB, with the microphone input disabled when in use. A high pass filter for the microphone and the DI input is switchable between off, 20Hz and 40Hz.