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Bass distortion-Playing LP's only,,,,please help

VPI Prime----Ortofon Black Quintet (low output moving coil cart)-----Plinius Koru Phono Pre( loading at 20 ohms/gain at 66 db)-----Parasound Halo Integrated -----Martin Logan Montis speakers which have powered bass cabinets.

Using any other source component I have absolutely no issues. When I play an LP and increase the volume past 10 O'clock which is a little loud....but not ridiculously loud-I at times get this huge wave of bass distortion. I do have bass controls on the Montis's...and I have turned them down into the negative, but I still get what I previously described occasionally. 

Any and all help would be appreciated. This doesn't always happen, but its frequent enough to drive me crazy.

Thanks in advance.

krelldog
tablejockey
3,922 posts
 
I just finished blasting a couple of cuts from  a couple of bass heavy records on my VPIClassic /ART9 at a level I NEVER use-2-3:00 o'clock. Just comparing what I heard during a demo of the exact model amp  at a dealers.

Cant imagine what the cause of your problem is. Be interesting to read what you find. I HATE having those isolated,quirky bugs!


mofimadness's avatar
mofimadness
4,993 posts
 
Sounds to me like you might be getting acoustic feedback/acoustic breakthrough/intermodulation distortion/rumble through the speakers.

This happens if the system is turned up too loud and the speakers are causing the arm/cart to excite. A rumble filter would solve this.

I’m assuming you checked all the alignment parameters of the turntable/arm/cart?
stereo5's avatar
stereo5
6,428 posts
 
I am willing to bet you are getting some feedback. Can you remove the grill and observe if the woofer is oscillating abnormally? If it is, its a feedback problem. I had this problem with my Scout and now my Prime. My turntable is on top of a rack on a solid 3 inch thick maple air dried platform which is sitting on a sandwich material I bought from Mapleshade. I still got it. I bought a KAB Rumble filter for 180.00 and put it through the tape loop. Now the problem is solved and I haven’t lost any bass quality. You should hear how subteranian it goes during some songs on Amused To Death.  I could rattle the fillings out of someone's teeth!
krelldog OP
323 posts
 
Wow.... I have never heard of a rumble filter....but it sounds spot on to my issue. My bass cabinets aren't accessible,so I can't confirm the rumble. However for 180 bucks its worth a try.... thanks guys.
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