"Pop" when relay closed or open.

flacman · 2017-12-21 11:06 am

I made a delay circuit for my headamp with this scheme. However, there is "pop" in the headphone when the relay is closed or open. How to fix it?
(My DC offset circuit amplifies only about 5mV)
Thanks a lot.

An externally hosted image should be here but it was not working when we last tested it.

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Thanks you very much for your comments.

My problem is "pop" sound when close/open relay. I have controlled relay manually (when my amplifier was stable).
I tried other types of relay, but the result is the same.

The "pop" sound loud when the relay is closed (when the headphone is connected to the amplifier) , while the relay is open, the "pop" sound is very small.

My amp is class A puss-pull, 130mA quiet current, dc offset about <5mV

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I thinks it is the reason

AndrewT said:
are you saying that even some time after stabilising that a maual change of the isolating relays that you still hear the pop?
That would confirm that the 5mV of offset is what you are hearing.
5mV offset for a headphone amplifier is too high.
5mVac is only 36dB below 1mW into 100ohms.
a 5mV step change into 100ohms would be just as loud.
For a 95dB/mW 100ohms headphone you would hear a 5mV pop as ~ 59dB SPL.
That is too loud.
5mV offset will also pull/push the diaphragm well off centre.

HotIce said:
If the pop is when the relay closes *and* open, then it is definitely a DC offset issue.

--
Sorry for wasting your time. (Im not mentioning from the beginning)
I'm afraid to write a lot, because my English is bad.

I will continue this topic to find more experiences of people using other popular consumer amplifiers.

I heard people say that:
- FiioA5 (psu +-11V) has not any noise when switching relay
- TrasamHa2pro (psu +-10V) has not any noise, too. But when the user replace the opamp with the Burson V5i opamp, the "pop" sound occurred.

Looking forward to your comments and experiences.
Thanks you very much!

JensH · 2017-12-27 11:00 am

If the amplifier has a DC offset you will get a pop when switching the relays on or off. So you need to eliminate the DC offset of the amplifier at steady state. How this can be done cannot be seen from the schematic you provided here.

Samsara · 2017-12-27 12:19 pm

flacman said:
there is "pop" in the headphone when the relay is closed.

If GND of relay contact and GND of headphone output are same and closed together , this is not possible.
I think you wrong with this schematic.

Mooly · 2017-12-27 12:42 pm

Just to expand on the above... if the headphone amp output is truly shorted to ground (at switch on by the relay) then depending on how the feedback is configured, the amp may not be able to correctly bias to the correct operating point.

HotIce · 2017-12-27 6:37 pm

Hmm, the amp output shorted to ground during the bootstrap phase seems like a recipe for fried output transistors

globalplayer · 2017-12-27 6:48 pm

That ground is bad.
Rather leave open.

JensH · 2017-12-27 10:16 pm

I don't see any basic problems with the circuit shown. The amp outputs are not shorted to GND. The circuit comes from this page:

Loudspeaker Protection and Muting

With the component values shown it does require a relatively high supply voltage, which may not be available in a headphone amplifier, but that is easy to change by changing component values.

But if the amplifier has an offset, even after stabilizing the DC operating points, there will still be a pop sound at turn on and off.

Mooly · 2017-12-28 8:02 am

The amp outputs are shown as grounded in the off state. Post #1, right hand side of diagram.

JensH · 2017-12-28 10:20 am

As I see it, the speakers are grounded, not the amp outputs.

Mooly · 2017-12-28 11:38 am

Oh yes, you are correct... my apologies for not looking closer at the earlier comments and my mis-reading the diagram.

Samsara · 2017-12-28 11:52 am

JensH said:
I don't see any basic problems with the circuit shown. The amp outputs are not shorted to GND. The circuit comes from this page:

Loudspeaker Protection and Muting

With the component values shown it does require a relatively high supply voltage, which may not be available in a headphone amplifier, but that is easy to change by changing component values.

You right.

JensH said:
But if the amplifier has an offset, even after stabilizing the DC operating points, there will still be a pop sound at turn on and off.

Only if the schematic is not adapted to the supply voltage, if adapted and have rational delay there will not be "PLOP" .
In this case (but need Flacman's confirmation and details), it seems there's no adaptation, and maybe the relay never switched off (GND to headphone/speaker).

dotneck335 · 2017-12-28 12:44 pm

Mooly said:
The amp outputs are shown as grounded in the off state. Post #1, right hand side of diagram.

NO, THEY ARE NOT!!! Look carefully---the SPEAKER connection is grounded, NOT the amplifier output---that would be silly.

Mooly · 2017-12-28 3:09 pm

dotneck335 said:
NO, THEY ARE NOT!!! Look carefully---the SPEAKER connection is grounded, NOT the amplifier output---that would be silly.

Please read ALL the posts.

Thanks

Samsara · 2017-12-28 5:17 pm

dotneck335 said:
that would be silly.

Not really because it's for protect speakers.
For example , Chevin A6000 have triac for short speaker output to GND if there's DC.
Of course, for professional during a show it's better to lose the amp than the speakers.

flacman · 2017-12-31 8:22 am

JensH said:
But if the amplifier has an offset, even after stabilizing the DC operating points, there will still be a pop sound at turn on and off.

My amp's DC offset are ~5mV (i think this is verry low).

The "pop" sound loud when the relay is closed (when the headphone is connected to the amplifier) , while the relay is open, the "pop"vsound is very small.

Samsara said:
You right.

Only if the schematic is not adapted to the supply voltage, if adapted and have rational delay there will not be "PLOP" .
In this case (but need Flacman's confirmation and details), it seems there's no adaptation, and maybe the relay never switched off (GND to headphone/speaker).

I don't know what you mean. I don't know what the word "adapted" means.
The relay in my circuit is closed/opened definitively.

Sorry for my bad English

flacman · 2017-12-31 8:25 am

Samsara said:
Not really because it's for protect speakers.
For example , Chevin A6000 have triac for short speaker output to GND if there's DC.
Of course, for professional during a show it's better to lose the amp than the speakers.

I think so. Speakers/Headphone are always expensive and more important than amplifiers. Thanks a lot for your circuit, I will integrate it into my amp to increase the safety.

Samsara · 2017-12-31 8:29 am

flacman said:
The "pop" sound loud when the relay is closed (when the headphone is connected to the amplifier)

If you hear it exactly when it's closed, it's not possible to hear any sound, because your headphone is grounded (according to schematic) .
You have to check your circuit.

Samsara · 2017-12-31 8:44 am

flacman said:
I think so. Speakers/Headphone are always expensive and more important than amplifiers. Thanks a lot for your circuit, I will integrate it into my amp to increase the safety.

It's useless , use relays.
Or you can use Mosfet as relays like Yamaha power amplifiers , here you can see they use Q112 & Q114 for +B rail for P5000S/P7000S

globalplayer · 2017-12-31 8:46 am

Clever.

flacman · 2017-12-31 9:08 am

Samsara said:
If you hear it exactly when it's closed, it's not possible to hear any sound, because your headphone is grounded (according to schematic) .
You have to check your circuit.

Yep. When the headphone is grounded, the "pop" sound is very small (may also be the sound of the relay's contact)
But when the headphone is connected to the amplifier, the "pop" sound is quite loud.

"Pop" when relay closed or open.

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