Loud pop on power off

[IA76]

Hi

We have a Behringer XR18 mixer and a Inter-M DPA900S amp. They are switched on via a switch that provides power to the socket that both these items are connected to.

When we turn the main power switch off there is a very loud pop over the speakers.

How can we stop this pop happening as apart from this everything works perfectly? What causes this pop as we have the same mixer/amp setup in another location and there you only get a very slight pop when powering off?

[Ynot]

It's generally regarded as good practice to power your amps on LAST when turning on the PA setup, and off FIRST when powering down.

When turning gear on/off the 'pop' is just a quick mains spike that can be 'heard' by audio equipment and sent down the audio path and in worst case scenarios (if that path is pre-amp'd enough) does risk blowing a speaker driver. 

Different gear may sound different, depending on how the gain structure is set up going towards the amps, but rest assured, the way to avoid potential damage to the gear is to be vigilant in your power up/down sequence.

 

[IA76]

Thanks @Ynot

The problem is that the audio equipment is kept in a different area to the hall where the audio usage takes place. They basically plug in mics to the mic points in the hall and switch on from the power switch.

Is there any type of 'gadget' that can be used to get around this issue or any other options as practically they have to switch off the equipment in one go from the main power switch in the hall.

[Brian]

One cause of this is poorly designed equipment where they've not properly dealt with residual charge on any DC blocking capacitors.

Q1) if the connection between the XR18 and the amp is removed I assume the pop goes away?

Q2) do you have a DI box to hand to interpose?

[alistermorton]

You can get a sequencer which will stagger the power up and power down sequence, which may go a long way to at least ameliorating the problem.

[dje]

This sounds entirely normal. I would expect a loud pop in the speakers if switching off the mixer prior to switching off the amps. The mixer will power down more or less instantly whilst the amp(s) will take a moment to discharge the capacitors and during this time they do remain 'switched on' to some extent... they will continue to amplify the input signal.

A power sequencer like here will alleviate this issue nicely.

[Brian]

1 hour ago, dje said:

This sounds entirely normal.

Normal? Not sure it's normal. Common? Definitely.

 

A properly designed system, using properly designed equipment, does not require a power sequencer.

[kgallen]

XR series can auto mute when the power goes (or more correctly can be muted when power comes up) but this might be a setting worth trying to see if the XR muting before the amp looses power helps your condition. It’s a tick box in the config settings (can’t remember the exact place and not near my XR16 to look…).

[IA76]

@Brian yes the sound goes away with no connection and we don't have a DI box.

 

Thanks for the advice all.

I have ordered this power sequencer and hoping I can just use the current power switch as a remote switch for it

https://www.avsl.com/brands/adastra/product/953.058UK-dp8-power-schedule-controller

Edited March 22, 2022 by IA76