Power Amp - "Pop/Tick/Click" speakers on startup ?

[onesixright]

Hi All,

I got a power amp and a pre amp. I switch the pre-amp on first, then the power amp, and I hear (once) a little "pop/tick/click" on one channel. Its actually in both, but the one seems slightly louder.

When I power-off, its also there but much software. Bot are grounded properly. After, it sounds perfect, no other problems whatsoever. Turn the volume all the way down (mute), makes no difference. So im guessing its in the power-amp.

What could be the reason causing this?

Thanks!

[amyk]

That's normal, just the sound of capacitors charging up. Remember that capacitors are used to AC-couple signals between circuits at different DC potentials, but to reach the steady state they'll need to charge up to the difference - causing a brief pulse of signal.

[onesixright]

Thanks.

Are you sure? I got another amp that doesnt do this. I spoke to the verdor, they want to have it in for service. Acknowledging it’s not normal.

I can hear a relay clicking on power on (that would be for what?). Any change that could have to do something with it?

I would just like to understand what causes this sound 

[Gyro]

The relay will be for speaker muting/protection - cutting the speakers out of circuit when the amplifier is being powered up or powered down (probably under DC offset fault conditions too) to protect them from voltage spikes.

If it's just a very quiet click through the speakers as the relay closes then that doesn't sound like a problem, just the tail end of the output voltage stabilizing or a very small DC offset. Nothing particular to worry about.

If the click/pop is louder then it indicates that there is probably a more significant DC offset, which needs the cause investigating or adjusting.

If you have a meter then you can do some diagnosis - turn on the amplifier and allow to stabilize for a few minutes. With the meter set to its lowest DC voltage range, turn the volume down to zero and measure the voltage across the speaker terminals (being very careful not to short them!) of each channel in turn. The DC reading should be very low - I would expect less than 50mV. If significantly higher then it indicates a problem.

[onesixright]

Thanks!

If you have a meter then you can do some diagnosis - turn on the amplifier and allow to stabilize for a few minutes. With the meter set to its lowest DC voltage range, turn the volume down to zero and measure the voltage across the speaker terminals (being very careful not to short them!) of each channel in turn. The DC reading should be very low - I would expect less than 50mV. If significantly higher then it indicates a problem.

I measured the DC voltage as you said:
- Left has 1 mV
- Right has 5 mV.

The "pop" on the right speaker is also louder (i guess because of the 5mV?).

Its not extremely loud, but you can notice it. And its not nice on the ears.

[Gyro]

Those levels are about as low as you could reasonably hope to expect from an audio power amplifier - absolutely fine.

It seems to me that you've become focused on listening for the click, you probably wouldn't notice it otherwise. Just think of it as the startup circuitry doing its job efficiently (as opposed to some amplifiers that give a nasty 'thump' or crack through the speakers at power on/off).

If all else fails, I'm sure the manufacturer will be happy to part you from a significant amount of money in order to perform a 'service' and return it to you with the same offset levels. 

[onesixright]

Those levels are about as low as you could reasonably hope to expect from an audio power amplifier - absolutely fine.

It seems to me that you've become focused on listening for the click, you probably wouldn't notice it otherwise. Just think of it as the startup circuitry doing its job efficiently (as opposed to some amplifiers that give a nasty 'thump' or crack through the speakers at power on/off).

If all else fails, I'm sure the manufacturer will be happy to part you from a significant amount of money in order to perform a 'service' and return it to you with the same offset levels. 

Hehe, thanks. Yeah indeed (over-)focused  . Try to unlearn that! ;-) But its definitely noticeable, the left (1 mV) is very low you need to put your ear in your speaker to hear it. The right is different, its louder and you can hear it clearly (standing in the middle of the room).

Well its, some would say high-end-ish. So i'm surprised, that in this price range, it pops. I did contacted them (NAD), they said bring it in. I was just curious what could be wrong. Another one I have makes no pop sounds (DENON). So thats what fuelled my curiosity.

[Gyro]

It's not unusual to see different offset voltages on the two channels, it can be affected by component tolerances, thermals, even PCB layout (eg. if output stage standing current is shared with feedback path for a short length of track). You just need to look at the offset voltage range spec for a typical opamp. It's amazing how low a signal you can actually hear through a speaker.

I would be wary of any suggestion from NAD which involves the handover of any cash - you have just carried out the test that they would do before telling you it's fine. The Denon might just have slightly lower offsets, or a slightly longer delay on the speaker relay.

[onesixright]

It's not unusual to see different offset voltages on the two channels, it can be affected by component tolerances, thermals, even PCB layout (eg. if output stage standing current is shared with feedback path for a short length of track). You just need to look at the offset voltage range spec for a typical opamp. It's amazing how low a signal you can actually hear through a speaker.

I would be wary of any suggestion from NAD which involves the handover of any cash - you have just carried out the test that they would do before telling you it's fine. The Denon might just have slightly lower offsets, or a slightly longer delay on the speaker relay.

I took it to the dealer. We hooked it up, and to my surprise nothing. Didn't hear a "pop".  Is there any change this could be cause by the mains power?

[shakalnokturn]

Pop-tick-click sounds like the wrong sequence, one would expect something more tick-click-pop. (Main power relay, speaker relay, DC offset.)
Are your DC offsets measured with or without speakers connected?
What model amp. do you have? Some NAD's are plagued by aged solders, that could explain why it is behaving since you took it for a ride.

[onesixright]

Pop-tick-click sounds like the wrong sequence, one would expect something more tick-click-pop. (Main power relay, speaker relay, DC offset.)
Are your DC offsets measured with or without speakers connected?
What model amp. do you have? Some NAD's are plagued by aged solders, that could explain why it is behaving since you took it for a ride.

Thanks.

Its a NAD M22. I measured it with the speakers connected. Sequence is OK ( ON: pre -> power, OFF: power -> pre).

[FlyingHacker]

Does it pop when connected to your speaker, but without any inputs connected? Perhaps there is some DC on your inputs or some other interaction with your other components. Are they all plugged in to the same outlet? It could even be an small arc in the power amp switch is being picked up as RFI by some other component, like your pre-amp.

[onesixright]

Does it pop when connected to your speaker, but without any inputs connected? Perhaps there is some DC on your inputs or some other interaction with your other components. Are they all plugged in to the same outlet? It could even be an small arc in the power amp switch is being picked up as RFI by some other component, like your pre-amp.

Thanks all to all of you helping!

I disconnected the inputs, same problem.
Plugged each power cable in the wall, same problem.
Swapped the speakers, same problem (right channel is louder).

NAD Cananda, now confirmed it could be in the mains net.

The dealer talked about a some power separator (cost > 1000 USD)?

With the speakers connected its quiet a task to move the stuff around the house to find another outlet

Would it be use-full hooking up the scope and measure the speaker output on power-on?

[coromonadalix]

service manual : http://akdatabase.com/AKview/albums/userpics/10007/NAD%20M22%20Service%20Manual.pdf

I dont see adjustments in the power amp section  like biais, dc ofsets etc ...   maybe check dc  voltages ripple around the zenners diodes to be sure, and the sub or main dc supplies line +vB -VB  ....

[shakalnokturn]

Well it could be caused by the mains power but that would be one of the last causes I'd expect.

Hooking up a scope is always a good idea 

A simpler way to check if it is a power-up transient is to connect the speakers once it is switched on.

I doubt it is a bad solder issue, not exactly an old model. The fact that it did not pop at the dealer's and pops at home could be because of speaker sensitivity, it can make a big difference.

I'm not sure about the rest of the amp ,but I do like the way the main SMPS is designed.

[Harb]

I have only very quickly glanced through this , but is the soft start Circuit functioning correctly........I had a similar issue once.

I would be looking very carefully at the relay. and its associated circuit.

[onesixright]

A simpler way to check if it is a power-up transient is to connect the speakers once it is switched on.

Good thought! I tried that. After power-up connecting the speakers you hear nothing.

I'm not sure about the rest of the amp ,but I do like the way the main SMPS is designed.

Besides the "plop", its  really a nice amp. Sounds great, especially since its Class D 

[onesixright]

I have only very quickly glanced through this , but is the soft start Circuit functioning correctly........I had a similar issue once.

I would be looking very carefully at the relay. and its associated circuit.

But it doesn't explain why it works on different mains?

[nfmax]

I doubt it is anything to do with the mains supply. It may be that the speakers used by the dealer are less sensitive* than your speakers, and/or that the ambient (acoustic) noise level at the dealer was higher

* i.e. they give lower acoustic output for the same input voltage

[onesixright]

It may be that the speakers used by the dealer are less sensitive* than your speakers

@shakalnokturn also mentioned this. I did't have any other speaker to test it, until I realised I can hookup my center speaker (unused).  Which id did.

Lo and behold! Nothing, pop is gone. Can I (we) conclude its the sensitivity of the speakers (KEF reference model three)? If so, anything you can do about it?

[shakalnokturn]

Well if it is a startup transient, you could always add a delayed relay between amp. and speakers.
I'm guessing it is a startup transient as most amp's I have worked on had DC offsets close enough to 5mv, sometimes higher, and I've never had any noticeable pop with those levels.
The Hypex NC400 modules are specified for up to 50mV DC offset so you can't really argue they are defective...

If 5mv is enough to make your KEF's pop and it isn't a start-up transient, then you'll want to get the DC offset as low as possible, it looks like the "R92" trimpot on the NC400 modules should adjust DC offset.

[Gyro]

It may be that the speakers used by the dealer are less sensitive* than your speakers

@shakalnokturn also mentioned this. I did't have any other speaker to test it, until I realised I can hookup my center speaker (unused).  Which id did.

Lo and behold! Nothing, pop is gone. Can I (we) conclude its the sensitivity of the speakers (KEF reference model three)? If so, anything you can do about it?

Yes there is. Just settle back and enjoy your very nice sensitive speakers, they will suffer less from thermally induced compression on loud passages.

Stressing about it is reducing your perceived sound quality.