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Roger Mayer Dottore XFM DR1

Passive Inductor Equaliser By Paul White
Published August 2022

Roger Mayer Dottore XFM  Passive Inductor Equaliser

Many of the best‑loved classic equalisers used a passive inductor‑capacitor (L‑C) circuit, in most instances followed by a stage of amplification to compensate for any level loss: the legendary Pultec EQP‑1A is a classic example of this approach to EQ design. According to designer Roger Mayer, a passive L‑C EQ works particularly well on the non‑symmetrical waveforms typically produced by most musical instruments and voices, which are not always treated optimally by a circuit that relies on negative feedback (as found in most general active EQ circuitry).

His Dottore XFM is a two‑channel, true passive L‑C equaliser based on high‑quality audio transformers; one of the transformer windings in each channel provides the necessary inductance. In bypass or boost mode, the Dottore XFM is also able to connect a balanced source into an unbalanced input without any loss in the signal level (typically you’d lose 6dB when feeding balanced...

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