[MichaelHiFi]

Trying to understand why I cannot play my turntable anymore. 

At any volume above less than normal, when trying to play an album (vinyl) the subs start pounding erratically.

What would cause this to happen?

[JohnR]

Feedback, perhaps.

[TomS]

Did you try the rumble filter switch on the sub amp? Seemed to help on mine.

[Art_Chicago]

Feedback, perhaps.

agree. Just covering  my 1200MK2 with its plastic cover fixed the problem for me

[MichaelHiFi]

Probably feedback agree. The rumble filter didn't change the problem. Weird....

[jtwrace]

It's probably because the V-Caps aren't burned in yet.   The electrons are confused! 

[MichaelHiFi]

It's probably because the V-Caps aren't burned in yet.   The electrons are confused! 

You know I thought about that. They (electrons) gathered together and are now in protest.

Burn-baby-burn 

[Danny Richie]

It sounds like your phono stage is passing some DC.

If the rumble filter doesn't kill it then that must be some massive DC. Any improvement with the rumble filter at all?

[HAL]

You might be exciting the cartridge vertical resonance.  This is usually in the low frequency range below 20Hz. 

Does the cartridge visually react to the bass energy?  If so, the cartridge and arm resonance is not being controlled properly.  Shure has a nomagraph that shows what the system resonance is using the effective mass of the arm and cartridge compliance.  That might give a clue as to what is happening.