Phono Question

[James Dalto]

Hi Guys, I need to use an outboard subsonic filter to solve a rumble problem with my analog set up. As I await the next phono kit I was wondering if it’s possible to modify the RIAA circuit to cut off the low frequencies?

[Jim Lambton]

Hey James! Back in my day, this was a common problem, mostly caused by inferior turntable designs and a lack of research on the materials side of things.

First YES you can install a subsonic or rumble filter, it would be in addition to the RIAA EQ circuit, not a big deal to design and install. But to catch the rumble you are going to remove important low frequency content from your music source. As an audiophile I can verify that having a good low end (bass) makes a huge difference to how your system sounds, without it, the sound is thin and lacks the underlying beat (drums and acoustic/electric bass). With it the music just comes alive.

So i’m going to suggest you fix your rumble issue. That probably involves upgrading to a modern quality turntable, but it could be as simple as a new shelf design or an auxiliary isolation platform under your existing table.

One thing that’s not well understood about turntable design and installation is the importance of isolation. First the motor needs to be outboard from the table (only the belt connects them), the table needs to have isolation feet (mine uses a 3 cone point system) and just as importantly the shelf needs to be isolated from vibration (if it’s a problem – for example your speakers or subwoofer are coupling to the shelf to the turntable).

The solution need not cost mega bucks, but for a great sounding vinyl system, it’s important to get this right. And even though subsonic filters used to be very common (due to poorly designed equipment), I would never install one in our Kit designs, for all the reasons mentioned above.

Hope that helps.
Good luck!
Cheers,
Jim

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