A balanced mic/line transformer typically wired for 1200 ohms (though 300 ohms is possible).

A single-ended common-emitter stage with active load (Q4). This generates most of the open-loop gain.

for their 80-series consoles. However, it is most famous in the DIY and boutique community for being "hot-rodded" into a high-quality microphone preamplifier. Core Sonic Character

The 1272 uses a 4-position rotary switch to set gain from +4 dB to +14 dB in roughly 3 dB steps. This is achieved by altering the negative feedback loop around the BA283.