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Seeking help with feedback through audio system

I currently use a high mass, direct coupled turntable and have been experiencing some strange "feedback" type issues - I will explain below.

I'd like to know if anyone else has experienced these type of problems and if there is a potential solution.

Situation:
My table sits on a wall shelf (massive & "home made") which connects/integrates with a load bearing wall. I have it set up this way because I have VERY springy hardwood floors which just don't work with any turntable (suspended or non-suspended).

Everything sounds great but at a certain volume level, I begin to hear what I presume to be feedback. It is a steady upper mid-range resonant tone which does not amplify or get louder, it just remains constant until a few seconds after the overall system volume is lowered. The feedback will continue between songs on a record but eventually gets drowned out by the next song and becomes less audible. I can faintly hear the feedback "within" the next song.

When the volume is lowered, the sound is great - with no feedback issues.

I presume this feedback is caused by the interaction between my room and the cartridge (Shelter 901) - which from what I've read may not be a good match for my unipivot tonearm - further complicating or enhancing the problem. I dunno. I did try moving the table to a different location within the room and the same problem occurred when the system was playing at about the same volume - however I think the frequency or tone-of-the-feedback-tone was a bit lower - perhaps mid-bass feedback.

Again, I'd like to know if any of you have experience anything like this and hopefully you've got suggestions on how to alleviate the problem.
bwhite

Showing 3 responses by bwhite

bwhite OP
807 posts
 
Dan and Bornin - thanks for the replies. Yes - it could potentially be a tube I will give that a try as well as try to dampen the tone arm & report results.

Bornin - yes... when I lift the tonearm, the feedback goes away.

What seems strange to me is that feedback typically amplifies or progressively gets louder. The situation I am experiencing is unique in that the feedback (or resonance or microphonics) remains at a constant volume. Weird.
bwhite OP
807 posts
 
Hi Doug, Good questions. This resonant feedback sound tapers off immediately when the volume is lowered and starts immediately when the sound reaches a certain (higher) level. Of course there is a curve in both directions where the sound tapers in or tapers out. Make sense?

The sound does sustain through the part of a record where silence should be (in-between songs) but stops immediately when the cartridge is lifted off the record.

Key here is that at a slightly lower volume level, there is absolutely none of this feedback.

I'll try to borrow another cartridge for test purposes as well as figure out a way to dampen the tonearm.
bwhite OP
807 posts
 
Hi Dan - its tough to tell which channel the feedback comes through. My system is (for lack of a better term) quite holographic - the speakers vanish and origin of any sound is for the most part quite difficult to determine. This resonant feedback sound in particular seems to emanate from somewhere in the room vs. from a particular speaker. I will disconnect one channel at a time and see if the feedback persists. This will certainly help to identify whether or not the problem is a nasty microphonic tube.

Maybe I should try some room dampening too.
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