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What can I do to minimize electromagnetic radiation from power amplifiers?

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solderdude

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The best way to avoid any electronic device to emit anything is to not use it.

Use an old wind-up grammophone if you want to reproduce music without any emission other than sound.

I would like to know why the OP is so fixated on this. Several years back there were a group of electrofog believers that claimed they could detect RF.
Because of a claim taken to court these folks had to prove their sensitivity. They were tested at the same EMC lab (DARE!!) where we also test our equipment. The guy that tested these extraordinary folks was testing our equipment so had a first hand talk about this.
These folks were tested in a shielded (and EM anechoic) room where RF (modulated and not modulated) was unleashed at them at various frequencies up to presumed safe levels (frequency dependent) as far as the equipment could generate (valid for lower frequencies). The goal was to detect when such signals were on and off at random intervals and AM modulations. Levels that would certainly upset many electronic devices.
The tests continued over several days.
To make a long story short there appeared to be NO relation whatsoever between 'felt' presence of RF and actual presence. No relation at all.
The conclusion of this test is not up to me.
 

March Audio

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The best way to avoid any electronic device to emit anything is to not use it.

Use an old wind-up grammophone if you want to reproduce music without any emission other than sound.

I would like to know why the OP is so fixated on this. Several years back there were a group of electrofog believers that claimed they could detect RF.
Because of a claim taken to court these folks had to prove their sensitivity. They were tested at the same EMC lab (DARE!!) where we also test our equipment. The guy that tested these extraordinary folks was testing our equipment so had a first hand talk about this.
These folks were tested in a shielded (and EM anechoic) room where RF (modulated and not modulated) was unleashed at them at various frequencies up to presumed safe levels (frequency dependent) as far as the equipment could generate (valid for lower frequencies). The goal was to detect when such signals were on and off at random intervals and AM modulations. Levels that would certainly upset many electronic devices.
The tests continued over several days.
To make a long story short there appeared to be NO relation whatsoever between 'felt' presence of RF and actual presence. No relation at all.
The conclusion of this test is not up to me.
Its the usual fear as a consequence of ignorance and lack of understanding.
 

Panelhead

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The CE certification requires the power line and air borne radiated noise meet the European standards. These are stringent.
If this Is a concern look for the CE on the back panel.
 

Mnyb

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The CE certification requires the power line and air borne radiated noise meet the European standards. These are stringent.
If this Is a concern look for the CE on the back panel.

Our host Amir is constanly nagging about it when CE or UL markings are missing , for a good reason . simply don't buy products without it ?
 

solderdude

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Around 0V (where X-over is close to) there is very little current, assuming resistive load.
 

kn0ppers

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And elsewhere? How about elsewhere? After it leaves Class A operation, doesn't it become an overbiased Class B essentially, with all the typical characteristics that come with Class B?

Bob Cordell - Designing Audio Power Amplifiers, Page 268,

13.10 Magnetic Induction Distortion
There are very distorted signals running around in class AB amplifiers. The biggest source of these is the nonlinear half-wave-rectified current in the output stage. Current flows from the positive rail on positive half-cycles and from the negative rail on nega- tive half-cycles. The magnetic fields created by these currents can induce nonlinear voltages in nearby signal lines, coupling distortion into the signal path [4].

This is the source he is referring to:
https://www.semanticscholar.org/pap...erry/20513860113d42207dae60a24ea56d4e28a10d0d
 

solderdude

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The current through the load is what determines the current through the output devices.
When this causes distortion it is also shown in the output signal under load.
The current through the output devices, in class B, is the same as through the load and that is a sine.
Only at the small class-A range current is passing through both output devices at the same time.
PCB design is paramount. Crappy design is crappy distortion levels under load.

I haven't seen any evidence that class AB operated designs emit substantial or even little emission due to the class-A to class-B transition phase.
 

kn0ppers

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Where have I said that the transition phase is the cause? Please don't turn my words around in my mouth.
 

Wombat

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Where have I said that the transition phase is the cause? Please don't turn my words around in my mouth.

You haven't said much at all. A generalised supposition or two, a quote from an unsubstantiated source, and lots of qvestions(reversal of onus of proof). :cool:
 
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solderdude

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Where would you look (measure) for evidence that class AB stages reaches potentially harmful and disturbing magnetic fields that would exceed emission standards for home equipment ? (otherwise it would not be considered harmful or would show up as distortion products reaching audible levels)
Would this not depend mostly on PCB design and shielding more so than AB operation ?
Other than an increased distortion of the output signal what would be the consequence ?
Would the emission be worse or equal than Switching amps ?
 
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Wombat

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I have said basically the same thing throughout: Class-AB output stages aren't all that harmless when it comes to their potential for causing potentially disturbing magnetic fields in power amplifiers.

Saying is not proving . Quoting a single non-authoritative source is not proof. Potential needs to be expressed in terms of probability and relevance.
 
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kn0ppers

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Where would you look (measure) for evidence that class AB stages reaches potentially harmful and disturbing magnetic fields that would exceed emission standards for home equipment ?
Would this not depend mostly on PCB design and shielding more so than AB operation ?
Other than an increased distortion of the output signal what would be the consequence ?
Would the emission be worse or equal than Switching amps ?

Okay, now you got me, sort of. The original thread was about radiated emission levels into the outside world. I knew that and I just made a remark about Class AB because I think it's often forgotten that even these can cause problems locally in the power amp itself, so I wanted to throw it out there. Then somebody said "HUH?" and I thought I should explain what I meant. I totally agree with you on your comments about layout, wiring and shielding and also on the thought that this mechanism will mainly cause distortion in the output signal.
 

Wombat

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Is it really a practical problem in typical audio listening systems?
 

mhardy6647

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Is it really a practical problem in typical audio listening systems?
I am not sure that the word practical really much applies in discussions like the present one. To paraphrase George Thorogood's paraphrase of John Lee Hooker's One Bourbon, One Scotch and One Beer
Everybody funny. Now audiophiles funny too.
;)

1600431516805.png
 

Panelhead

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Guess this is not much different than discussing if a dac or amplifier that has a SINAID of 116 sounds twice as good as one that measures 110.
A reality check for me. I use Eupen Hospital grade power cords. They are shielded, and also have a simple LC filter inside the molded wall plug. The stated purpose is to limit the noise dumped back into the home electrical wiring. Should filter in both directions.
I assume these EU made power cords were prior to the latest CE standards. The manufacturer of my amps boosts they set CE and other certifications.
Far as only buying UL or CE certified audio products. Consider scale. If building batches of 100’s of units at a time this should be a given. The “cottage” builders who cobble equipment on order or build one unit at a time cannot shoulder the time and other resources to meet the requirements.
I build some of my gear. Try to look for others mistakes to improve my projects. This website has helped a lot.
 

FrantzM

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Trolling by any other name ...
They got some of us going..
I was out , staying out.:mad:
 

MakeMineVinyl

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What are you "HUH?"ing me about? Assuming a sinusoidal signal and a load that requires the Class AB output stage to leave class A, what do the currents through the output devices look like?
The output transistors are never completely turned off because of the bias current, and there are no transients generated when they reproduce their half of the signal.
 

solderdude

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The output transistors are never completely turned off because of the bias current,

This is not true. Depending on the emitter resistors voltage drop and drawn current the not used transistor can actually get a BE voltage below the point where it conducts as the bias voltage is working as a Zener.
Some efforts were made to ensure the not active transistor remained conductive but differences are not very big.
 
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