Kab RF-1 Rumble Filter
Getting into LP's and startled at the big speaker cone movements that you're seeing? Thinking a better turntable will help? It may not! This very low frequency energy is called rumble. Much of it is actually cut into the record groove when the master disc was made. Other sources are mis matched tonearms, poorly damped tonearms and acoustic feedback. Often, the only way to suppress rumble is with a really good rumble filter.
With rumble eliminated, the soundstage becomes more "still" and the bass actually tightens up because the woofers are no longer modulating and the power amp is no longer wasting current resources on sub audible noise.
The KAB Great Sound Escort RF-1 is a very fine transparent rumble filter that not only suppresses very low frequency (subsonic) energy, but also uses a unique active cancellation circuit that effectively suppresses vertical rumble too. Your subwoofers will thank you! Suppresses acoustic feedback too.
Two important things to know:
1. When records are made, frequencies below about 150Hz are combined to mono. This is done to avoid large out of phase groove excursions.
2. When the stereo stylus moves vertically, the two signals produced are equal and 180 degrees out of phase.
Therefore, below 140Hz, the music is in phase in the lateral stylus motion, and only out of phase noise is found in the vertical stylus motion.
The KAB RF-1 takes advantage of this by electronically combining the left and right channels together below 140Hz. In so doing the filter effectively cancels vertically modulated noise. Vertical rumble comes generally from bearing noise of the disc cutting system. But since the music below 140hz is already mono on the disc, the musical information is unaffected. Below 20Hz, all signals are quickly attenuated at 18dB/Octave.
The RF-1 is a must for vinyl enthusiasts.
The KAB RF-1 is easy to install. Place it in between the phono preamp and control amp or in a process loop. It requires no attendance. It is happy to remain powered up at all times.