Do you hear “pop” when you turn off your amp?

[Evenharmonics]

I now have 2 TubelabSE amps (1 stereo & 1 mono) and stereo one turns off quietly but the monoblock makes a loud “pop” from the speaker when I turn it off. Last night as an experiment, I unplugged IC cable from the monoblock before turning it off and guess what, no “pop” at all. I use Rane AC-22 active crossover to feed these amps and was wondering if it has something to do with input signal or grounding. Is anyone familiar with this noise when turning off an amp? Thanks.

 

[Jeb-D.]

Yes, some amps I've had do that. There are to things you can do to get rid of it.

You can place a small value capacitor across the switch terminals
or
Put a metal oxide varistor (MOV) in parallel with the primary side of the transformer but after the switch.

Edit:

Sorry, I didn't read your entire post saying how it doesn't happen with the interconnect disconnected. The fixes I mentioned above are for power supply transients caused by the switch. They may not be helpful for your circumstance.

 

[Iain McNeill]

IC = interconnect?

There should be a soft start circuit which should perform fast stop function to protect speakers in the event of brown outs.

Can you measure any DC offset on the IC cable that could cause the pop?

Does the stereo amp pop when you connect it to the mono IC cable (alleged cause of pop)

Does the mono amp not pop when connected to the stereo amp source.

These annoying little things can be a PITA to debug. Good luck!

 

[Burnedfingers]

Are you turning the amplifiers off first followed by the other equipment or are you powering everything off at once?

 

[Evenharmonics]

IC = interconnect?

Can you measure any DC offset on the IC cable that could cause the pop?

Yes, IC = interconnect.

DC offset on the IC cable? You mean, put multimeter lead across "hot" and ground contact of RCA plug?

Does the mono amp not pop when connected to the stereo amp source.

I just tried it and it does not "pop" when one of stereo IC is connected to mono amp.

Are you turning the amplifiers off first followed by the other equipment or are you powering everything off at once?

Amp is off first, then active x-over and everything else in reverse sequence of turning on.

 

[Iain McNeill]

certainly looks like an input related issue.
DC offset may only me a few mV so you need to convince yourself what you're seeing is real. reverse test probes for identical -ve result, both leads on +ve test point etc should be 0mV etc.etc.

Measure unplugged and in-circuit for both mono amp and stereo amp source. That data set should reveal something.

What other factor could affect the power down of the amp? It's all about dumping the charge in the PSU caps, right? When the mains supply stops, the feedback loop fails and one polarity of the output will turn full on and collapse that rail.

I like the hard-stop circuit, as long as the PSU caps hold up for the relay turn off time, you never get pops.

 

[HighVividity]

My "wintersweet highvividity" amplifier makes a pop when I turn it off. Of course there is the trick of turning down the volume before turning it off.

 

[Decker]

No, I don't live with my parents anymore.

 

[kevinkr]

First it is not a particularly good idea in a tube amplifier to disconnect the load to avoid a turn off pop, that little transient with load connected could turn into a bigger transient with no load, and under extreme circumstances result in large voltages across the primary of the OPT.. Relay not recommended..

Secondly it is not unlikely that the power switch is the culprit, your pop could be emi from the arc across the switch coupling into the input of your amplifier via the IC.. As previously recommended try a cap across the switch. A HV ceramic in the range of 0.01uF/1KV or similar line rated X or Y cap may do the trick.

 

[Iain McNeill]

the relays are usually NC/NO changeover so you can switch from speaker load to resistor load if you want to.

He said the pop went away when connected to the stereo source.

 

[Evenharmonics]

your pop could be emi from the arc across the switch coupling into the input of your amplifier via the IC..

Where the monoblock is located within the room, it may be more susceptible to RFI because I did notice a bit more noise floor (buzz) from the speaker when I put my ear within an inch from it compare to stereo amp. By the way, the buzz disappears when I unplug IC cable from monoblock. Could this be an important clue?

the relays are usually NC/NO changeover so you can switch from speaker load to resistor load if you want to.

I'm not sure if I understand those.

 

[wakibaki]

A single-pole changeover relay has 5 pins, 2 for the coil, 1 Normally Connected or Closed, 1 Common, and 1 Normally Open.

When the coil is not energised the Common pin is connected to the Normally Connected pin and the Normally Open pin is open circuit. When the coil is energised the Common pin is connected to the Normally Open pin and the Normally Connected pin is open circuit.

w

 

[Wavebourn]

Stopping of high freq oscillations due to lowered emission and plate voltage may cause a pop. Ground wire to the input socket might be soldered to a wrong place.

 

[Evenharmonics]

Ground wire to the input socket might be soldered to a wrong place.

???
There are only two solder points on female rca plug. One at the center for input signal and the other one at the washer for ground. They are soldered correctly. I do have this washer as chassis ground contact point as well. That can't be the cause, can it?

 

[fdegrove]

Hi,

As an experiment, mute or at least turn down the volume of your preamp.
Make sure no source is still "playing" then turn off your amp(s).
If the problem persists it may be an arc over problem inside your amp in wich case a small cap across the turn-off switch' contacts may help.

Cheers,

 

[Wavebourn]

???
There are only two solder points on female rca plug. One at the center for input signal and the other one at the washer for ground. They are soldered correctly. I do have this washer as chassis ground contact point as well. That can't be the cause, can it?

It can be the cause. A chassis has resistance and inductance. If your power supply is connected to one side of the chassis, output tube is connected to another side of a chassis, the current flowing through it causes voltage drop that is the higher the higher is the frequency and the current, so if to feed this voltage back to amplifier's input through cable's capacitance the amp may oscillate. I'm not familiar with George's design and your implementation, so my assumption is more theoretical than based on your particular situation.

 

[nigelwright7557]

First it is not a particularly good idea in a tube amplifier to disconnect the load to avoid a turn off pop, that little transient with load connected could turn into a bigger transient with no load, and under extreme circumstances result in large voltages across the primary of the OPT.. Relay not recommended..

Secondly it is not unlikely that the power switch is the culprit, your pop could be emi from the arc across the switch coupling into the input of your amplifier via the IC.. As previously recommended try a cap across the switch. A HV ceramic in the range of 0.01uF/1KV or similar line rated X or Y cap may do the trick.

I would go for the capacitor across the mains switch too.

I used to have a dual record deck for my disco with mains switches to drive the turntable motors and I would get a huge crack through the loudspeaker when I switched the switches on or off. A cap across the switches made a huge difference.