Prevent power-on pop to amplifier

Thread Starter

surfdabbler

Joined Oct 7, 2013
11
I'm designing some audio circuitry (simple 2-to-1 mixer box) that feeds into an amplifier. Currently, we have to follow procedure to power on the amplifier last, and power it off first. preventing the dreaded pop. However, as I'm building a new box in the sound chain, it would be nice if there is some passive circuitry that could get rid of the nasty power on/off pop if my mixer box is turned on or off while the amp is on. Is there any standard circuitry that I could add to the output of my mixer to provide this function?
 
Last edited:

Halfpint786

Joined Feb 19, 2018
109
More of a question for others here than a possible solution (in other words, 98% guessing here)..

Would a 10k resistor (or even 100k) to ground on the input side of the DC blocking capacitor work? That way, when the amp is powered on, the bias network slowly charges the capacitor to the bias voltage instead of suddenly trying to charge it when the capacitance of a cable is connected.
 

Thread Starter

surfdabbler

Joined Oct 7, 2013
11
Yes, it might be worth some experimenting with this. At the moment, I don't even have DC blocking capacitors, but I'll be getting them later this week. :)

By the way, I am working with balanced audio throughout.
 

Thread Starter

surfdabbler

Joined Oct 7, 2013
11
The standard circuitry is a speaker relay that has a delay on power on.
Yes, we have that feature built into the amp, but the amp is on a separate power circuit at the other end of a large room, and is powered on/off separately from the mixer. Maybe we should run power from one power point so that everything is powered on/off together. That is a possibility, although it will require rerunning either power or speaker cables through the walls/floor/ceiling. I would have to test whether this also solves the issue on power-down if everything turns off together.

Edit to add - I just thought of another scenario where we can't enforce everything to power on/off at the same time, as there is regularly used 'ad-hoc' equipment that must be connected to a different power source. We can suggest power on-off sequence protocol, but we can't enforce it.
 
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drjohsmith

Joined Dec 13, 2021
852
wonder whats causing the pop
Ok we know the pop is caused by the speaker cone suddenly moving,
but that means a voltage is applied to the speaker, what's causing that ?

When you turn the amp on , with nothing connected to its inputs , do you get a pop ?
if so , then the pop is caused by the amp itself,
The answer then is to either get a new amp that does not pop,
or add a power on delay circuit to the output ,
typically as mentioned, that would be a relay , that at rest has the speaker disconnected, an a RC delay to the coil of the relay and the power supply, that after say a second and the amplifier is stable, connects the speaker to the amp
If this does not fix it, then the amp is putting a DC bias onto the speaker, which is in itself not good.

If you have to have something connected to the amp input , to get the pop
that indicates it coming from down stream,
For instance a DC bias on the input to the amp would cause a pop when the amp is turned on
 

MrAl

Joined Jun 17, 2014
11,496
Hello,

In converter circuits there is such a thing as a "slow start" mechanism. This slows down the output during power on. Instead of the output jumping right up to maybe 12 volts, it starts out low like 0v then ramps up slowly to 12 volts. The time it takes depends on how long you want it to take.

To do this with an amplifier, you would add a transistor or two to the main power supply and during power on it would charge the power supply capacitors up slowly, maybe over 1 or 2 seconds.

Sometimes it is caused by the volume control pot. You can check and see if the pop still occurs if the volume is turned all the way down before you turn off the amplifier, then turn it back on and see if you still hear the pop. If not, then sometimes you can add a capacitor to the pot arm to help charge another capacitor already in the circuit. You may have to have a schematic for this though.
 

Thread Starter

surfdabbler

Joined Oct 7, 2013
11
wonder whats causing the pop
That's a good question. It's not the amp. Turning the amp on/off doesn't cause the pop, because the amp has self-protection against this, as people have mentioned.

Plugging cables in and out also doesn't cause a pop. I'm pretty sure it's something like a power-on spike. As the sound source is turned on, perhaps one balanced signal line comes on before the other, or perhaps one jumps briefly to 12V while the other jumps to -12V, before settling back in on the correct values.

In converter circuits there is such a thing as a "slow start" mechanism. This slows down the output during power on. Instead of the output jumping right up to maybe 12 volts, it starts out low like 0v then ramps up slowly to 12 volts. The time it takes depends on how long you want it to take.
The slow voltage ramp-on/off would be a worth trying. I can also try the relay or opto-isolator approach, delaying the signal connection until after power is on, and disconnecting the signal lines immediately on power-down, maybe using a cap to keep the circuit powered up until after the isolator or relay is disconnected.

Thanks for the ideas.
 

drjohsmith

Joined Dec 13, 2021
852
That's a good question. It's not the amp. Turning the amp on/off doesn't cause the pop, because the amp has self-protection against this, as people have mentioned.

Plugging cables in and out also doesn't cause a pop. I'm pretty sure it's something like a power-on spike. As the sound source is turned on, perhaps one balanced signal line comes on before the other, or perhaps one jumps briefly to 12V while the other jumps to -12V, before settling back in on the correct values.



The slow voltage ramp-on/off would be a worth trying. I can also try the relay or opto-isolator approach, delaying the signal connection until after power is on, and disconnecting the signal lines immediately on power-down, maybe using a cap to keep the circuit powered up until after the isolator or relay is disconnected.

Thanks for the ideas.
Sounds like its not the amp then
I think you say something a while back about not having the AC pass capacitors in circuit yet ?
that could be the cause

Basically , you have two options,
a) fix the source that's causing the pop
b) "Clamping" the speaker till the pop has gone

I'd say that (a) is the way forward,
find what's causing the pop
 

MrChips

Joined Oct 2, 2009
30,824
Depending on the design of the amplifier there might be a DC blocking capacitor feeding the loudspeaker.

1672493883641.png

If the power amplifier uses a bipolar power supply then the output capacitor can be eliminated.
Bridged amplifier output does not require the output capacitor.

If the single output stage is driven by a unipolar supply voltage of Vs, the output capacitor has to be charged to ½Vs. This causes the "pop" on power on and also on power off.

High power direct coupled amplifiers might not be properly DC balanced. Large currents can destroy loudspeakers. Thus DC coupled amplifiers will measure the DC voltage at the output before energizing the speaker relay.

Most, if not all, audio amplifiers are AC coupled in some part of the audio chain. These are often coupled with 10-47μF interstage capacitors. I have not examined the charging effects of these capacitors on power on/off.
 

drjohsmith

Joined Dec 13, 2021
852
Depending on the design of the amplifier there might be a DC blocking capacitor feeding the loudspeaker.

View attachment 284242

If the power amplifier uses a bipolar power supply then the output capacitor can be eliminated.
Bridged amplifier output does not require the output capacitor.

If the single output stage is driven by a unipolar supply voltage of Vs, the output capacitor has to be charged to ½Vs. This causes the "pop" on power on and also on power off.

High power direct coupled amplifiers might not be properly DC balanced. Large currents can destroy loudspeakers. Thus DC coupled amplifiers will measure the DC voltage at the output before energizing the speaker relay.

Most, if not all, audio amplifiers are AC coupled in some part of the audio chain. These are often coupled with 10-47μF interstage capacitors. I have not examined the charging effects of these capacitors on power on/off.
@MrChips
I'd agree with you
but the OP has stated the amp does not pop when its turned on and off, nor when an input is connected or removed
I'd assume from that its not the amp thats a problem.
 

Art Mezins

Joined May 26, 2019
11
There are lots of potential causes as discussed, with nuances of each. BTW: It's not a "AC passing" capacitor, it's a "DC blocking" capacitor. It they are partially charged, then depending on the discharge impedance, a charged one can produce a spike. Even a lousy ground loop when connecting equipment together (e.g. various preamps, including microphone, into a mic preamp and its output both have DC blocking caps). This is a system issue that needs investigation with a good isolated Oscope (so it doesn't introduce more noise). Make sure all subsystems have a "good" common ground and power distribution. While an protective fuse is good for protecting equipment, especially for catastrophic conditions, the designer may rely on them to do too much (e.g. compensate for poor design and/or thorough testing).

I also disagree with dismissing "connecting inputs" as not being problematic, because they can be. Just maybe not "all the time".

I had a 1500 W Samsung combo Blu-ray 7.1 audio system that had "startup" issues with pops and an assortment of noise until one of the channels blew out (I never bothered to locate the fault, since I had better things to do).

Remember, anything that has to charge or discharge (L or C!) are candidates, but that includes delayed or sequenced power (transients all, just not impulses) or relays. Transients may not be able to be eliminated, but they can generally be mitigated so they aren't as onerous.
 

MrAl

Joined Jun 17, 2014
11,496
That's a good question. It's not the amp. Turning the amp on/off doesn't cause the pop, because the amp has self-protection against this, as people have mentioned.

Plugging cables in and out also doesn't cause a pop. I'm pretty sure it's something like a power-on spike. As the sound source is turned on, perhaps one balanced signal line comes on before the other, or perhaps one jumps briefly to 12V while the other jumps to -12V, before settling back in on the correct values.



The slow voltage ramp-on/off would be a worth trying. I can also try the relay or opto-isolator approach, delaying the signal connection until after power is on, and disconnecting the signal lines immediately on power-down, maybe using a cap to keep the circuit powered up until after the isolator or relay is disconnected.

Thanks for the ideas.
Oh so you have a problem when it turns off too? That could take a little more work but there should be a solution.
 
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