feedback

Re: feedback

Postby Dorian » Mon Jun 05, 2017 6:11 pm

miner wrote:Dorian, your opinion of the Symposium inserts please.

Hi Miner

I have no point of comparison sorry as I put them in when the table was brand new, before I even listened to it.

I can report that I've fixed my feedback problem. I did lower the bearing cup to an 1/8th", it helped a little but not much. So I then moved the speakers another foot further away from the turntable and that fixed it for good.
VPI Prime #959 & Outer Ring| SoundSmith MIMC Star | Herron VTPH-2A | Primaluna DiaLogue Premium HP Integrated | KEF LS-50s | Phoenix Eagle & Roadrunner | Audio Sensibility Cables | Symposium Ultra | AQ Niagara 1000 | Stillpoints LPI | Focal Clear
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Re: feedback

Postby audiom3 » Fri Feb 16, 2018 6:27 pm

I too have this issue all of a sudden. Everything is fine until the volume gets up to around 70-75dBs. Then my woofers oscillate like crazy. I've added too many upgrades recently to narrow it down, so I'll try this first when I get home. Fingers crossed.
Classic w/ 3D arm & VTA Tower; Kiseki Blue N.S.; Benz Micro Wood SL; Sutherland 20/20 Phono Preamp
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Re: feedback

Postby audiom3 » Sat Feb 17, 2018 9:57 am

My arm spike was too high, so I lowered it at least 1/4" but no change in resonance/feedback. Should there be more mass (spacer, etc) UNDER my bell/VTA chassis?
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Classic w/ 3D arm & VTA Tower; Kiseki Blue N.S.; Benz Micro Wood SL; Sutherland 20/20 Phono Preamp
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Re: feedback

Postby Harry » Fri Mar 02, 2018 3:30 pm

This business of the woofers pumping and the feedback is usually caused by low output MC cartridges being fed into phono sections that have no subsonic roll off or no subsonic switch that you can engage. You are amplifying low frequency garbage between 500 and 1000 times when you are using a low output MC, this should be cut off so your amps do not kill themselves reproducing essentially noise!

It seems the designers of late have spent to much time playing with digital and have forgotten or never knew that every receiver, integrated, and preamp of the vinyl age had a sub sonic filter you could engage or was built in. If you do not cut off the below 15HZ garbage your amps are trying desperately to reproduce it starving the music of power and dynamics. For me, if it does not have a subsonic filter a phono section is a non starter.

Now, if you have a high or medium output MC, Let's say over .4 mV it becomes less of an issue or almost no issue when you get up around .8 or 1 mV and your cartridge naturally rolls off. MC's that go down to 5 HZ and have ,25 mV output not only require a subsonic filter, they demand it. Of course no one ever mentions this because it might affect sales!!!

Then there is the feedback issue which the subsonic filter handles nicely. Combine that with an arm properly setup, tracking force correct, and the mass matched to the compliance of the cartridge you will have no issues. BEST OF ALL IS A CONCRETE FLOOR!!!!

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Re: feedback

Postby Johnny » Fri Mar 02, 2018 3:45 pm

Harry, I don't see a front panel user defeat subsonic filter on the new VPI Voyager phono pre-amp? Is it incorporated into the circuit design? If so, it would be worth mentioning in the literature.
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Re: feedback

Postby audiom3 » Sat Mar 03, 2018 8:45 pm

A special thanks to Harry for helping me solve my issue. He's exactly right. I spent hours and hours researching and trying every idea I could find online. Nothing worked. So I ordered and installed a KAB RF-1 and the woofer oscillation is completely gone - even well above 100dBs. Not that I listen at ear splitting levels but it's nice to know I could without worry of the house exploding. No down-side to using it. I was expecting to lose bass but actually gained.
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Re: feedback

Postby Harry » Mon Mar 05, 2018 12:06 am

The Voyager has a roll-off below 20HZ and will not pump woofers.

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