[jcoat007]

Some time ago I posted about a problem I was having with low frequency feedback when I use my turntable at fairly hefty volumes.  What happens is that as I turn the volume up, you can actually feel the drivers in my subs shaking the room.  Bass gets really muddy and diffused and eventually it's like an earthquake in my room.  I then have to turn the volume down to get it to stop.

Funny thing is that I had to have my tonearm repaired and at the same time I acquired a Butler 2250 amp.  I put the repaired tonearm in place simultaneously with the Butler.  

I was happy to find that the low frequency feedback was gone and I attributed it to the repaired tonearm and upgraded pivot.  

So yesterday I switch out the Butler for my Odyssey Extreme Monos, and guess what?  Low frequency feedback is back.  At higher volumes everything falls apart and there's an earthquake going on in my room.  

Is it possible that the Butler does not extend as low as the Odyssey and therefore does not exhibit the same problem?  

The specs on the Butler say: Freq response: 20Hz to 20kHz (+/- 0.5dB)
The specs on the Odyssey say: 2 - 500,000Hz

Those differences would seem to indicate that the Butler does not extend as low or as high.

I admit that I do not have an ideal setup and my equipment is right smack in the middle of my speakers and subs, but I do not want to limit my choices of amps to solve this problem.  I guess I need to find a way to better isolate or relocate my turntable.

[woodsyi]

What are your room modes?  Does resonant feedback happen with CDs as well?

[jcoat007]

What are your room modes?  Does resonant feedback happen with CDs as well?

It only happens with my turntable.  

I do not know what my room modes are.  I need to figure that out.

[woodsyi]

If it is just the TT, here is my theory.  You have a room mode around 30Hz or something that is below Butler's reach but not Oddyssey's.  That resonance provides enough vibration to affect your TT  to somehow go haywire on bass.  I don't know how -- I am just guessing.  If you can do a quick wall mount with mdf shelf, hooks and wires or even hang the TT on your ceiling temporarily, you can test my theory.

[Ethan Winer]

JC,

> as I turn the volume up ... <

This might be exagerated by room resonances, but that's not the basic problem. The main issue is simple mechanical coupling between the turntable cartridge and the loudspeakers. This usually happens when sounds travel from the speakers through the walls and/or floor to the cartridge. But it can also happen acoustically in the air.

There's an easy way to test this: Pick up the turntable in your hands so it's not touching what it usually rests on, and have someone else turn up the volume. If you can turn up the volume higher than before without getting feedback, then an isolation pad or equivalent under the turntable is all you need.

--Ethan

[lonewolfny42]

Is it possible that the Butler does not extend as low as the Odyssey and therefore does not exhibit the same problem?

Simple answer...yes. Comparing the Butler with other amps, their low end is not as strong as other amps. And yes, I've heard Odyssey, and I own a few other amps. [/list:u]

[jcoat007]

There's an easy way to test this: Pick up the turntable in your hands so it's not touching what it usually rests on, and have someone else turn up the volume. If you can turn up the volume higher than before without getting feedback, then an isolation pad or equivalent under the turntable is all you need.

That's easier said than done.  Trying to play a record while holding the turntable in my hands was not possible.  As the needle bounced around the table, I quickly ended that experiment.  

What sort of isolation pad would you use?  I am using a Neuance shelf under my TT right now.

[zybar]

There's an easy way to test this: Pick up the turntable in your hands so it's not touching what it usually rests on, and have someone else turn up the volume. If you can turn up the volume higher than before without getting feedback, then an isolation pad or equivalent under the turntable is all you need.

That's easier said than done.  Trying to play a record while holding the turntable in my hands was not possible.  As the needle bounced around the table, I quickly ended  ...

If possible, mount your turntable on the wall with a wall shelf.  When I had my Linn LP12, that was the only way to really isolate it from vibrations coming from the speakers and floor.

George

[jcoat007]

If possible, mount your turntable on the wall with a wall shelf.  When I had my Linn LP12, that was the only way to really isolate it from vibrations coming from the speakers and floor.

George

I just purchased one.