Why Preamps Thump on Turn on

There are some amps that get an inrush of power and cause a thump some people developed relays as a solution to this.my old carvers are an example and aftermarket has a no thump circuit  for this

Interesting ...

I have an old NAD 7220PE coupled with Spectrum 208A speakers that I acquired for dorm life way back.  Powering up would also produce a rolling 50hz burp ... 

Have a Holman APT pre coupled with Odyssey Kismet amp, which are dead-silent.

Kind of miss the burp ...

I am often reminded how difficult it is to write something that others find fun and engaging. 

Agreed with audioman58.
I would always turn on the source components first, then preamp, then power amp last. And when shutting down my system I would always power off the power amp first, then preamp, then source components last. it’s dead silent, no thump.
That thump is DC still on the line like what audioman58 described above.

Carvin Audio Explanation. Substitute Preamp for Mixer.

"THE RIGHT ORDER TO TURN THINGS ON

Before anything else, let’s review the power up sequence for a common live sound scenario. Power up in this order:

1. Sound sources like keyboards and synths that are connected to the mixer
2. Mixer
3. Power amps
4. Powered speakers and stage monitors

1. PROPER POWER DOWN SEQUENCE

   As you might imagine, spikes occur when you turn equipment off as well. Since all the gear is on before you start powering down, you’ll need to power off in the opposite direction (first in last out). So in the example above, active speakers and power amps would be turned off first (so they don’t receive a spike from the mixer), then the mixer…and finally the onstage gear connected to the mixer."

Some power controllers have sequenced power banks that do this for you.