My amp made an extremely loud pop when turning off

[olds1959special]

One of my four Kenwood L-05M’s made an extremely loud pop when I powered it down with the power button. Why did this happen? None of the other amps did that. I have been trying a new tube pre amp but I don’t see how that’s related? (I’m going to use the mute button on the preamp before turning on and off just in case, but not sure why that would make a difference) I turned it back on and off to test and everything works now, and fortunately music still plays as it should. I have old wiring in my house, and use three prong to two prong adaptors to plug in my power strip and small power conditioner. Any ideas what happened? Recently another amp I had, a Rotel, randomly popped and stopped working here. Not sure if there’s any relationship? My tube pre is buzzing slightly in the left channel, and I’ve had that issue before as well with a Rega Brio I once tried here. Right now I have all four amps plugged into a power strip, along with the preamp into the same strip, which is plugged into a small Furman power conditioner, which then goes to the 3 prong to 2 prong adapter and into the wall. I am turning all the gear on and off with their own power buttons, although for a few days I was using a power strip to turn on all the power amps at once, and also to power them down. I might go back to that for convenience. (I tried plugging everything into the same power strip to fix the buzzing but it didn’t help)

 

[Tinker]

What is your shut down sequence? Turn down preamp volume and shut off amp first and wait a few seconds for it to power down. Then shut off the preamp, then dac, then streamer in that order.

Hope this helps!

 

[olds1959special]

What is your shut down sequence? Turn down preamp volume and shut off amp first and wait a few seconds for it to power down. Then shut off the preamp, then dac, then streamer in that order.

Hope this helps!

I turned off the amps without turning down or muting the preamp first. Then I turned off the DAC. But will hit the mute button on the preamp first from now on. Turning down the volume is not needed with the mute button working, I guess.

 

[olds1959special]

Is it a faulty switch on one of the Kenwoods? Should I bypass and use power strip to power on and off?

 

[Tinker]

I turned off the amps without turning down or muting the preamp first. Then I turned off the DAC. But will hit the mute button on the preamp first from now on. Turning down the volume is not needed with the mute button working, I guess.

Did the pop happen when you shut down the DAC ?

 

[olds1959special]

Maybe the buzzing in the preamp is from bad caps in the power supply. But the power amp popping is from a faulty switch or what is arcing?

 

[olds1959special]

Did the pop happen when you shut down the DAC ?

No the Dac is always silent. But I turn it off last anyway.

 

[Tinker]

I would shut down the amps and let them sit a minute or two. Turn down/mute preamp. Give it a try.

 

[olds1959special]

Btw all the red and black speaker wires are reversed based on the instructions of the preamp to invert phase.

 

[olds1959special]

I wonder if it’s a faulty switch? I’m going to power up with a power strip from now on, to bypass the switch.

 

[Speedskater]

Don't connect it to your best speakers until you solve the problem.

Pro audio turn on/off sequence.

Power on:
1] sources
2] controllers
3] amplifiers

Power off:
1] amplifiers
2] controllers
3] sources

 

[JeffS7444]

I might check to see if there's any significant amount of DC at the preamplifier or power amplifier outputs.

 

[olds1959special]

I might check to see if there's any significant amount of DC at the preamplifier or power amplifier outputs.

If it’s coming from the pre, would muting the pre before shutting down amps help?

 

[Tinker]

If it’s coming from the pre, would muting the pre before shutting down amps help?

No harm in trying.

 

[olds1959special]

No harm in trying.

I accidentally turned off the amps without muting it and nothing bad happened, so I’m guessing thats not related?

 

[MaxwellsEq]

A single instance is very tricky to diagnose. I've spent frustrating hours in studios trying to reproduce a one-off fault. If it's only one of four amplifiers that did it, the problem is with THAT power amplifier and/or the feed to it.

BUT given your comments in other threads about your recently added, popping, buzzing valve preamplifier, I wouldn't rule the preamplifier out. Muting it won't help if it's the output stage misbehaving. There may be DC on the output of the preamplifier (use a voltmeter on DC to check). The simplest fix will be to bin the preamplifier since you don't need it. Then you can see if the loud pop reoccurs.

 

[Tinker]

I accidentally turned off the amps without muting it and nothing bad happened, so I’m guessing thats not related?

The preamp isn't going to somehow send a signal through, bypass the amp and cause a pop if the amp is shut off. However, you MUST let the amp sit for a minute. Otherwise there may be enough current left in the amp capacitors to pop.