Why Preamps Thump on Turn on

I posted a fun discussion on my blog to get into the details of this turn-on phenomenon. 




I leave my preamp on 24/7 - same as my amp. Both transistor. No thump from either on turn on/off. 

I turn on my McIntosh preamp and it then turns on my Mac power amp and Mac tuner,  No thumps or pops in my system.

This happens with asr amir too - in his rush to have a reply for everything in making response to anything, he too never reads first much, in then making an answer to an entirely different issue of his own manufacture. 😆

When turning on  digital I always leave on , 

then preamp ,then amplifier,

when shutting off , Amplifier then preamp, in that order is the correct way.

that thump is DC still on the line,  do you have a tube preamp ?

if so follow this sequence.

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.


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



    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.

I've always read proper turn on sequence is:

1. Preamp along with everything connected to it.

2. Amp.

Shutdown is the opposite

 BUT..... My preamp is connected to my amp with a wire that turns both on at the same time when you do a startup with the preamp remote control.

 Neither the preamp nor the amp instantly come on, there's a few seconds of delay.

 You can here a click in each when they actually power on. I assume this makes the startup procedure okay? Just want to be sure, thanks.



Amplifiers should always be turned on 1st and last off!  This will eliminate speaker thump due to large current inrush filling capacitors in the amplifier.

I follow the instructions provided to me in my Aesthetix Callisto Eclipse line stage preamp. Power it up first and let it warm up for at least ten minutes prior to powering up my CJ LP27M monoblocks. Shut down is the reverse order. With this, I've never heard an in rush thump

Amplifiers should always be turned on 1st and last off! This will eliminate speaker thump due to large current inrush filling capacitors in the amplifier.

The inrush current is the same whether first or last.  However, turning it on first will cause the amp to amplify any thumps caused by upstream components, if any.

The amp may cause the AC voltage to dip momentarily, but that's not a problem for any other components that are already on.

IMHO, the correct way to avoid thumps is as follows:

Power on - source, preamp, power amp.

Power down - power amp, preamp, source. 

The above works well and is completely silent.

@erik_squires I should point out that in that article, the myth that a tube preamp produces a large Voltage spike is promoted. That’s usually not the case with them. Solid state has been around 60 years or so; I think we’d have been hearing about this way back in the 1970s or some such if it was really real.

The reason is that most preamps have a cathode follower output, which does not put any Voltage on the coupling capacitor at the output of the preamp until the tube begins to conduct. The Voltage thus applied to the coupling capacitor rises quite slowly, much more so than that of the power supply! So you don’t get that spike as shown in the graphic on your site.

You get a shallow dome-shaped waveform instead:

Since its a cathode follower, the Voltage spike will never be at full B+. And because proper design practice is followed, the output coupling cap has some sort of resistance to ground at its output, discharging the cap. So it might reach 0.5Volts during this. If a very large coupling cap is used you might see something higher, but that cap is very large because the designer meant the preamp to drive a solid state amp with a low input impedance. When it is doing so, the capacitor is discharged much more quickly. As a result, if you were to have the amplifier on while the preamp is warming up, you’re far more likely to get thumps because of prior circuits to the output warming up at the same time (like the phono section, which can be avoided by having the volume down) than anything to do with the output of the preamp.


@atmasphere   Thanks for the follow up... I'll have to go take a look when I have time, which may be a while.

@erik_squires  Huh?? you have enough time to post that and then direct people to your site with this thread, yet not enough time to take down obvious misinformation? That'll take only slightly longer to sort out than it will for you to respond to this thread.

@atmasphere Wow that is some serious entitlement there. I’ll get to it when I get to it.  I had time then, i don't right now.  Sit and spin until you cool off.

My Levinson ML-26 preamp has no power button. When it's plugged in or unplugged, it releases horrid noise way worse than a thump.  I was always careful but we had some sort of power glitch and the preamp went off while the power amp still had some current, and it blew a tweeter in my Magnepans.  

The problem was the power glitch, but actually a malfunction of a Monster power conditioner I was using.  That sucker was retired quickly.  

None of my other preamps do this. My Proceed power amp thumps when I turn it off, but only when connected to my BAT tube preamp.  Otherwise quite as can be.