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KAB Rumble filter gets preamp to overload/distort?

So, I have always hated to see the woofers on my speakers bouncing around while playing vinyl no matter how well I chose and set up my systems (all of my turntables-arms-cartridges exhibit a resonance frequency around 9-10 hz). I decided to give the KAB rumble filter a try to eliminate this problem. I got it today and it works without having any apparent effect on sound quality until i notice something WEIRD:

I usually set the gain on my Manley Steelhead for the Clearaudio Maestro around 50-55db . While playing a London FFRR LP of Askenazy playing Rachmaninoff's preludes, I heard some distortion very much like the breaking-up sound of mistracking on both channels. I was so scared that was something wrong with the Maestro and it was eating up my record, so I immediately stopped playing and took it under a microscope to check the stylus..To my relief, it still looked very much like new (about a year old but playing sparingly and always on new, clean records), so I proceeded to check the tracking force, anti-skating and everything is fine. I took out a test record to roughly check the tracking and BOTH channel buzzed like crazy that I thought the cartridge's suspension was out or something.

At this time I didnt know what else to check rather than thinking of finding someone to give the cartridge a complete health check, then with a very faint hope, I decided to just use the Steelhead's lowest gain to see how it went and voila..the distortion disappeared.

My particular analog rig never acts like this, and the Clearaudio Maestro - Moerch DP6 red dot - Thorens TD-124 has been a tracking champ, so the culprit must be the newly added KAB rumble filter!

I took it out of the chain, ran the test on both 50db and 55db gain and everything is fine..no tracking distortion, no overload!

I will try to contact KAB to find out what the problem might be, but meanwhile, can anyone explain why a rumble filter can cause this distortion??

Does anyone has this type of problem with KAB rumble filter before?

Thanks
jaytea
Post removed 
jaytea OP
78 posts
 
No..the KAB is connected between the phonostage and the preamp. Kevin @ KAB emailed me and said a MM cartridge with a 5mV output and 55dB gain could overload the KAB filter. The Clearaudio Maestro has an output of 3.6mV but I guess this could happen. Perhaps my assumption that the KAB is just a filter and it will output whatever comes into it (after filtering the low rumble) is wrong, since it CAN be overload. I'll try to contact them just to make sure.
rpfef
110 posts
 
I had the same experience with the KAB filter when I switched preamps.
The problem, according to the designer of the new SS preamp (Reflection Audio OM-1), is that the tape output is not buffered, whereas it was buffered on my old one, a tube design. Therefore I could not use the tape loop.
I do not know how common it is the have an unbuffered tape out but potential users of this fine rumble filter should be alert to this possibility.
actusreus
733 posts
 
It's an overload issue, just as Kevin explained. 50-55 dB of gain for a cartridge with an output of 3.6 mV is way too much. 55 dB works well with my Delos that has an output of 0.6 mV,six times less than the Maestro. I've had the KAB in my chain for a few years now, with no overload issues. Go to the KAB website and plug in the output into the gain calculator, and adjust your Steelhead accordingly. I would expect the sound to improve as well, no overload aside. I'd expect that much gain to make the highs shrill and edgy in the great majority of set-ups.
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