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Here's one for ya Part 2

So,this am the cartridge plays fine.I do have hum but only when I turn the pre up.No hum with a signal.But what I have now is a horrible case of acoustic feedback.So I took the table down and put a heavy patio block on the wall TT shelf.This has always done the trick with other tables.But I still have acoustic feedback.Come to find out I only have acoustic feedback with the clamp on! I tried it loose,tight still feedback.I tried a rubber puck I have also but still feedback.
With no clamp no prob.I have the Delphi level and set up so when I push down on the platter it bounces 3 times then stops.I was told this was correct.
Any thoughts?
I would like to thank Tom for all his help in my return to vinyl.Thanks Tom (aka TWL)
david99

Showing 2 responses by twl

twl
3,251 posts
 
Dave, try relocating your TT onto a stand. This may change the nature of the vibrations that are reaching your platter. It is also possible that the TT is in a place in the room which has alot of bass excitation. Having the TT on a stand would allow some movement to experiment with the placement, and perhaps cure or reduce the problem. You might try just moving your speaker(s) temporarily to different areas of the room, and see if this cures it. If it does, then the feedback is related to the location of the TT with respect to the speaker location. Then you could move the equipment rack and TT to a spot that does not seem to cause the problem.
twl
3,251 posts
 
Dave, the feedback issue is based upon whatever frequency vibrations are getting through the shelf into the TT. You might try using various weights on the shelf, and see if you can find a particular weight that brings it into a zone the TT suspension can handle. I think the reason that using the clamp makes it worse, is that the record is somewhat de-coupled when not using the clamp, so it doesn't get affected as much. From what you describe, the vibrations at a certain level and frequency are defeating the suspension and getting right up to the platter.

I think that there will always be somewhat more noise with a high-gain phono stage, but it shouldn't be a "hum". I don't think your Creek is the problem. But even a small grounding issue in the TT area will be fed through the high gain phono section and sound alot bigger than it might be otherwise.

Your room extension seems to be a "funnel" for reflected waves from the room, and focusing them on the equipment. This could be a large part of the problem. Try some standing diffusors or maybe even a bass trap in front of the TT/equipment. Even a couple of high back chairs in there to see if you can break up the wave-fronts, so you can see if there is any improvement.

Just a few guesses to try.
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