WarmGain Subsonic Filter

Description

The WarmGain Subsonic Filter is an inline passive filter that connects between the output of a phono preamp and the input of an amplifier, rolling off frequencies below 20 Hz at 18 dB/octave. Below 20 Hz lies a zone of frequencies that are inaudible to human hearing but fully audible to a woofer cone — subsonic energy from record warp, motor rumble, and airborne feedback drives the woofer to large, silent excursions that waste amplifier power, stress the woofer suspension, and create intermodulation distortion in the audible frequency range.

Why Subsonic Energy Damages Your System

A warped record produces a pitch-modulation event at the frequency of one rotation — approximately 0.55 Hz for a 33 RPM record — plus harmonics. This subsonic energy is reproduced faithfully by the phono preamp and fed to the amplifier at full level. At high volume or with inefficient speakers requiring large power:

– Woofer cone excursion at 1-5 Hz can reach or exceed mechanical limits, causing voice coil rub or surround damage
– Power amplifier clipping on subsonic peaks reduces headroom available for the audible signal
– Intermodulation between bass fundamentals and subsonic modulation degrades midrange clarity
– The WarmGain Subsonic Filter rolls off at 18 dB/octave below 20 Hz — three poles of filtering

Installation and Signal Path

The WarmGain Subsonic Filter connects inline between the phono preamp output and the amplifier input using standard RCA cables:

– RCA input on one end, RCA output on the other — no power supply required
– Unity gain at all frequencies above the 20 Hz cutoff — does not alter the audible signal
– No active components — no noise, no distortion contribution from the filter itself
– Compact extruded aluminium housing — 110 × 50 × 35 mm, fits in any equipment layout

Compatible with any phono preamp output. Backed by a two-year warranty.