Burwen Research DNF 1201A Dynamic Noise Filter

Burwen Research DNF 1201A Dynamic Noise Filter — tested and working.

A single-ended dynamic noise filter from the late 1970s, designed by Richard Burwen. Unlike Dolby or dbx, it needs no encoded source — it works on any program material, so it's useful for cleaning hiss off reel-to-reel tapes, cassettes, 78s, off-air FM, and shortwave audio. The filter tracks program content, sliding the high-frequency cutoff down during quiet passages and opening back up on transients so you keep the top end where it matters.

Condition: Very good. Faceplate and knobs are clean with only light handling marks from normal use. [Note any specific nicks/scratches here.] All switches and controls operate smoothly with no scratchiness. Rubber feet present. Serial #[fill in].

Testing: Powered up and passed audio through both channels. Filter action verified audibly — noise reduction engages and defeats correctly via the front panel. Tape monitor loop functions. No hum, no channel imbalance, no intermittents.