In the volumes of email I receive I get some great questions. Mark, in San Jose California, was asking why phono preamplifiers no longer offer switchable rumble filters.
I think it’s a great question. I remember years ago when nearly every phono preamplifier had a switchable rumble filter and I also remember hating it. Every time I clicked that filter all the bottom end of the recording seemed to vanish along with the unwanted woofer movement. Those high-pass filters of the day were pretty aggressive.
PS Audio has been building phono preamplifiers since our inception in 1974 and we have never offered a switchable rumble filter. However, every one of those preamplifiers had built-in rumble filters and that, Mark, is the most likely answer to your question.
By building in a fairly aggressive filter we can keep its frequency low enough so as not to negatively affect sound quality. We do this with a multi-pole high pass filter that has the dual role of keeping any small DC issues from occurring and, at the same time, eliminating rumble without impacting bass.
I am going to guess that what’s actually different is not the lack of rumble filters, but the lack of switches to toggle them on or off.