RF1 Subsonic Filter

by KAB


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. But the main source is feedback exciting the natural stylus/arm resonance between 7 and 12 hz. This produces a slow easily visible in and out motion of your woofers. If you cannot see this motion, the RF-1 will not solve your feedback problem. If you can see this motion, the RF-1 will solve your feedback problem.

And 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. 

The RF-1 is a must for vinyl enthusiasts, live DJ's and when burning CD's for the car. You probably can't hear it, but your car woofers are going mad with all that subsonic rumble!

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. 

Maybe it's the costly marketing, I don't know, but it really is not all that expensive to include hi quality parts like Wima propylene capacitors and gold/teflon RCA's. Yet the sonic advantages of doing these things is unquestionable.

Unique active vertical cancellation circuit "monos" the low frequencies below 140 Hz. This suppresses vertical rumble and the "wump" "wump" of warps.

All steel construction wards off the effects of stray magnetic fields.

The KAB RF-1 is on all the time. It has no on/off switch or power light.

The really great features to take note of with the RF-1 are, I believe, the product uniqueness. You simply do not see the rumble filters being offered anymore. Yet the need for these special devices is growing.

One of the biggest let downs with phono playback is subsonic rumble. Often part of the recording itself, even the best turntable will reproduce it. And with todays cross over video and music entertainment systems, response down to 10 Hz is common.
A good rumble filter will actually improve the bass response by removing those deep subsonic dynamic swings from the system altogether. The power amp breathes easier and the woofers can concentrate on the music at hand.

Unique to vinyl records:
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 follows the KAB tradition of true single ended Polar Stable design. This technique operates the circuitry in a constant state of preconditioning(often called Burn In). This ensures a very consistent sound quality that never waivers.


  •  -3dB @ 20 Hz 18dB/Oct
  •  Unique Active Vertical Cancellation below 140 Hz
  •  Dual Voltage Regulation
  •  Output 5 Vrms
  •  THD <0.05%
  •  Noise -95dB
  •  Dimensions 4.5" x 3" x 1.25"
  •  Shipping Weight 4 Lbs
  •  Power: 24VDC,0.75A Meanwell GE18I24-P1J


  • 1 Year Warranty
  • Gold Teflon RCA's
  • Active Vertical Cancellation
  • Dual Voltage Regulation
  • Wima Propylene Caps 
  • Metal Film Resistors
  • Star Grounding 
  • Steel Chassi
  • Hi Current Power Pak


KAB RF1 Subsonic Filter
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