RF1 Subsonic Rumble Filter

Getting into LPs 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. The main source is feedback which excites the natural stylus/arm resonance between 7 and 12 hz. This resonance produces a slow, easily visible "in and out" motion of your woofers. If you see this motion, the RF1 will solve your feedback problem. If you don't see this motion, the RF1 will not solve your feedback problem.

With rumble eliminated, the soundstage becomes more "still", better defined, the bass tightens up because the woofers are no longer modulating and the amp is no longer wasting its power resources on sub -audible noise.

The KAB RF1 is a very fine, acoustically transparent rumble filter which suppresses very low frequency (aka subsonic) energy, by using a unique active cancellation circuit to effectively suppress vertical rumble and acoustic feedback, too! Your woofers will thank you!

The RF1 is a must have for vinyl enthusiasts, DJs and can even be used when transcribing LPs to digital! Even though you might not be able to hear it, your woofers are likely going mad with all that subsonic rumble in the signal path.

The KAB RF1 is easy to install. Place it in between the phono preamp and the preamp or in a tape-loop. The RF1 requires no maintenance and it's designed to be powered up at all times. 

KAB builds the RF1 with very high quality parts, such as Wima propylene capacitors, high quality resistors and and Teflon insulated, gold plated RCAs. The sonic advantages of using these great parts unquestionable.

Subsonic rumble is one of the biggest let downs with vinyl playback. Frequently, this rumble is "baked" into the recording itself and even the best analog rigs will be susceptible. Audio systems now are much better than when a lot of the music we listen to was recorded and frequently our systems have a heck of a lot more low-bass power than was even dreamed of just a few short decades ago.

A good rumble filter improves the system's bass response by removing these deep subsonic dynamic swings (aka low-frequencqy noise) from the system altogether. The amplifer breathes easier and the woofers can now concentrate on the music at hand.

Please note: For optimum performance, the RF1 needs to be positioned between the Phono Stage and the Preamp (or Integrated Amp). If that's not possible, connecting the RF1 in a tape-loop so it can be switched in and out as necesssary is the next best solution. In an all-analog system where there is no outboard phono preamp, the RF1 may be installed between preamp and amplifier. Installing the RF1 between turntable and phono preamp is possible, but not advisable, as this can introduce noise.

• Delivers -3dB filtration @ 20 Hz with an 18dB/Octave slope
• Unique Active Vertical Cancellation below 140 Hz
•  Dual Voltage Regulation
• Teflon insulated, Gold Plated RCA for inputs and outputs
• Wima Propylene Caps
• Metal Film Resistors

• 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.

• Unit is powered on all the time, no on/off switch and no noisy power light

• Star Grounding
• Steel Chassis
• Hi Current Power Pak
• 1 Year Warranty

Max Output: 5 Vrms
THD: <0.05%
Noise Floor: -95dB
Dimensions: 4.5" x 3" x 1.25"
Ship Weight: 2 Lbs
Power Consumption: 24VDC@ 0.75A
Power Supply: 100-240VAC @ 50/60Hz (Included)

This section offers a bit more in-depth info on the RF1's operation than the other tabs. If you're new to vinyl or don't like it when your head starts to spin from too much info, you can safely skip this section. However, if you like peering behind the curtain to see how the magic's made, here's the skinny!

Traditionally, when records are made, all frequencies below approximately 150Hz are summed to mono. This is done to avoid large out-of-phase groove excursions, which would otherwise be possible. When a stereo stylus moves vertically in the groove, the signal produced by both channels are equal and 180 degrees out of phase. Below 140Hz, the music is in phase in the lateral stylus motion, so only out-of-phase noise is found in the vertical stylus motion. 

The RF1 takes advantage of this characteristic by electronically combining the left and right channels together below 140Hz. In so doing the RF1 effectively cancels out vertically modulated noise. This noise is primarily generated by the main bearing in the disc cutting system. Since music below 140hz is already mono on the disc, the musical information is unaffected! Below 20Hz (i.e. no longer musically relevant), all signals are quickly attenuated at an aggressive 18dB/Octave.

The RF1 follows the KAB tradition of true single ended Polar Stable design. This technique operates the circuitry in a constant state of preconditioning which ensures highly consistent sound quality which never wavers.