The Quicksilver has a subsonic filter. I think it soulds good too.
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If the subsonics are on the record and not a result of the arm/cartridge (mis)matching I'm not sure how much help the filter might be. I have a TC with a sub sonic filter and a couple of LP's which cause substantial woofer excursions. I put the filter in line but it made no difference, on or off. If its just a couple of LP's, don't play them. :-) If it happens on a lot of LP's, look at set up/matching issues. A subsonic filter is, IMHO, a cheap bandaid used to cover up a major problem.
No band-aid, a subsonic filter is essential if you're using a good subwoofer -- or your main speakers extend really low -- and you're trying to play vinyl. There's all kinds of subterranean garbage on LPs that the engineers probably didn't even know they were recording. Like those subway trains that are all too audible on many early London (English Decca) LPs recorded at Kingsway.
One thing sure, if your woofers are trying to play this stuff, they're definitely screwing up the sound of the low frequencies you WANT to hear. Dave
Dopogue, Apparently my response was ambiguous.
FWIW, my reference to a "bandaid" was to using a subsonic filter to mask a problem in the cartridge/arm matchup. The effect of mis-match will creep up into the audible frequencies if you don't correct the problem - by using a subsonic filter you just stop the woofers obvious flapping.
As to using a subsonic filter to solve software encoded information problems, do what works for you. I was just pointing out that mine did not work for me with the problem the original poster was referring to.
But here's a thought - if you can actually hear it in playback its probably not really subsonic, so a filter meant to really apply to the subsonic frequencies might not extend high enuf to affect audible frequencies. Perhaps my filter was truly a subsonic filter which rolled off before it got to the 20hz zone. Don't have the stats on the filter so I really don't know. Just a thought mind you......
Distortions caused by subsonics are audible. Though the filter can cause some vailing it is still preferable to the distortion and speaker/amplifier demands caused by subsonics. If it is important to you to be able to deactivate the filter for good recordings it may be worth while to get one that uses a switch rather than jumpers to activate the filter. However I would prefer to have a phono-pre that does everything well (Project Phono Box SE or Tube Box) than one the just has the capability to switch quickly. Even with the subsonic filter implemented on one of these phono-pres you are likely to see an improvement over anything cheaper that offers subsonic filter.