Woofer pulsating with no volume , Oscillation issue?

Hello all - I just picked up some new Harbeths and as I was listening I noticed the left woofer moving kind of peculiar....I turned off my source & the woofer was actually pulsating in & out with no source volume. 

I have Manley Snappers . I switched sides (speaker cables) with no input & the problem followed to the other side....must be some kind of amp oscillation issue Im guessing...? Thanks for any troubleshooting help- 


It sounds like a bias/offset issue.  I'm not a tube head but contact the manufacturer or your dealer.


ya , the left amp has a bias reading all over the map , should be 300 & its jumping radically...did contact Manley about all this, looks like it's headed back to the shop.....thanks

It could be nothing more than a bad tube. Try swapping them left for right first.

Start with the power tubes.

If it doesn’t follow the tubes, then most likely needs service.

I should add, the woofer pumping, and the bias bouncing around are most likely related.




A low frequency oscillation as you see here can be caused by failing filter capacitors in the power supply. If this is the cause it will get worse- the condition is known as 'motorboating'. If this is what is going on, I'd have both monoblocks serviced as its likely the caps in the other channel will follow suit soon.

@tommypenngotti In that case you have the two most likely candidates:

1) a tube that is making mostly low frequency noise, which would result in irregular motion in the woofer

2) a regular motion is most likely a failed filter cap, even one that is only 6 months old (we've certainly seen that enough to know it can easily happen)!