things that go thump in the night and the day

[pucho812]

So I get a call about a distribution amp that got power cycled and goes thump thump thump repeatedly on the outputs.  The unit it self is plug and play with trim pots  for level adjustments and is less then a half rack wide.  real basic commercial audio and broadcast kind of thing, doesn't even have a power button.  The unit is at a place I have done tech work for before, it's also part of a system I installed but did not spec out or anything.

I call tech support for the manufacture as it's not a unit I am  not familiar with.  Well tech support says the units are designed to be left on all the time and connected.  Do not turn them off.  That when we do turn them off, it is normal to hear thump thump thump at power up for around 5 minutes as the unit has a ramp up time for bias currents  and when under biased it will thump, it will also thump if you are maxing out with level at the opamps.  That if the unit still thumps after an hour, then there is a problem with the unit. 

So as it's thumping away,  unplugged the outputs and plugged them back in. The outputs are wired to an edac connector and we just disconnected and reconnected the edac. that got the thumping to go away. I am not sure what exactly that did though, or if it was just coincidence that  thumping stopped after we did that.
While we are back to working, I am  wondering what is going on?

 

[JohnRoberts]

Creative customer service... If it thumps when you turn it on, never turn it off....   Sounds like that old joke about the guy who goes to the doctor and says his arm hurts when he moves it like this. The doctor says don't move your arm like that.  ;D

ironically perhaps cheap value products invest more design effort in turn/on noises because value customers will assume the worst and not buy a sku that burps or farts at turn on/off.

JR

 

[pucho812]

Creative customer service... If it thumps when you turn it on, never turn it off....   Sounds like that old joke about the guy who goes to the doctor and says his arm hurts when he moves it like this. The doctor says don't move your arm like that.  ;D

ironically perhaps cheap value products invest more design effort in turn/on noises because value customers will assume the worst and not buy a sku that burps or farts at turn on/off.

JR

Well it has no power switch, so I assumed long ago it never shuts off.  power outage on the grid, unavoidable.