Subsonic Rumble Solutions

Thanks for your suggestions, but I still think the problem is more inherent to the medium than my setup.

My racks are about 200 lbs each. Each shelf is it's own seismic sink with 50 lbs of sand in them. They are spiked to a cement floor. My TT itself weighs about 30 lbs (plus the motor which is about another 30 lbs). I am also using a Mark Kelly designed motor controller (think SDS), which makes the motor dead quiet. That's not the source of any vibrations either.

See here: http://cgim.audiogon.com/i/vs/i/f/1155818474.jpg

and here: http://cgim.audiogon.com/i/vs/i/f/1155818602.jpg
(note: bubble wrap is replaced by squash balls which proved much better at isolation from the shelf)

The subsonics are definitely not due to speaker interaction, since it happens on the lead in groove right away, before anything is playing. It is visible on the regular speakers too, when the sub is on or off. This is not an isolation problem due to standing waves in the room, but a rumble problem due to low signal vinyl interaction with the cartridge and phono stage.

Therefore: standard subsonic issues with vinyl. I even tried damping the tonearm, with no affect on the subsonics but a lack of air and life to the music - so that's been reversed now.

I spoke with Jim Hagerman about this and he said he purposely did not limit any extension at either end, making the Trumpet very wide bandwidth. He suggested changing out the .22uF inter-stage coupling caps to .1uF as a possible partial solution. I did this with no obvious change (however they are now upgraded to RTX's).

Please keep the ideas coming. At this point I think the answer is going to be electrical (e.g. a rumble filter), but I'm open to trying other suggestions first.

Thanks,
Bob

Is the Corian material a great option to use for plinth? I only ask because I have a DIY Corian arm-board on my SOTA and question its immunity from feedback.

Thanks for the link Fap. Is this filter available in a kit form, or just the schematic as provided? Where does it plug in, between the cartridge and phono stage or after the phono?

I assume the whole signal rides through it ... if so then I assume the op-amps affect the entire signal. So I would expect that different op-amps might affect the overall sound in different ways - no?

You mentioned an increase in apparent available power, so maybe it adds a bit of gain also?

What phono stage are you using with it? Did you notice any affect on transparency or soundstaging or the top end?

Thanks,
Bob

When I built it I was told that Corian is dense and fairly inert. It certainly is heavy (and pretty to look at), but I often question the same thing as you. I have toyed with the idea of applying a heavy piece of aluminum or some such to its bottom as an additional damping solution. But I have trouble trying to figure out how to attach it sufficiently and whether I should put some EAR Isodamp or some such between it and the Corian (e.g. constrained layer damping of sorts).

Bob

Hi Bob, yes circuit boards are available for the circuit, but all components need to be sourced by the constructor. All parts are easily available from the usual parts shops.

The filter input is connected to the output of the phono stage. I also use the Elliott Sound Products P06 phono stage which actually has an extended low frequency end. The P99 filter cleans up all unwanted cone movement due to warps etc completely. 18 Hz is where my filter starts operating.

As the amp is no longer trying to reproduce all the unwanted subsonic rubbish, there is more power available for the real music! Regards, Fap.