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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
3,934 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
4,995 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
6,441 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.
lewm
13,220 posts
 
Krelldog, Better to move either your turntable or probably just one of your woofers (if they are separately housed).  Though the rumble filter will probably do the job, it's another item in the signal path that probably you could get along without.  Filters are not entirely transparent.
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