The Neve microphone preamplifier 1290 was the same circuit found in the legendary 1081 & 1073 channel strips. This build adds the HPF from the 1073, to cut low frequencies during tracking, when necessary.
The HPF uses an inductor to form a resonance filter, with 12 dB per octave rolloff. The control has 5 frequency set points.
This build uses Madriaanse circuit boards (from groupdiy). Carnhill transformers, tantalum caps, 184c transistors. The output stage is transformer coupled through the transistor, operating in class A.