# Radio interference from D class amps



## Omicron (Jul 15, 2018)

I have two D class amps that are causing radio station interference (I popped the fuses out and interference is gone). I know the way to try to fix this is to move the amps around (turn 90 degrees or so for mounting to see if the interference goes away as the position of the amps can cause interference with whatever booster the auto manufacturer uses to get signal to the shark fin antenna). However, I am wondering if there is any device out there that someone has used to alleviate this type of issue without re-mounting the amps? The space I have is limited and is going to now house a larger box, so moving the amps is going to be problematic for airflow, etc. Any assistance is appreciated.


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## minbari (Mar 3, 2011)

Not that I am aware of. The switching freq that the power silly uses is to close to FM radio freq. You can try a faraday cage for the amplifier 

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## Holmz (Jul 12, 2017)

Is the interference transmitted out of the amp in a radiated fashion?
Or is it going out of the amp on the positive of negative leads?
(You'll need a scope, and maybe a little antenna)


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## Mike Bober (Apr 11, 2013)

I had that problem with Class D amps in a 2011 Camaro with the shark fin antenna exactly 27" above the amps that were in my trunk.....i had to switch over to class A/B amps to eliminate that interference. I had to move the Class D to far away from where i wanted it to get rid of the interference. Not sure if it was the brand of amp or just the Class D type, but i read a bit about it being the D amp so i switched and all is great now.


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## Omicron (Jul 15, 2018)

minbari said:


> Not that I am aware of. The switching freq that the power silly uses is to close to FM radio freq. You can try a faraday cage for the amplifier
> 
> Sent from my LG-LS998 using Tapatalk


Thanks. I will see what I can come up with for a cage.


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## Omicron (Jul 15, 2018)

Holmz said:


> Is the interference transmitted out of the amp in a radiated fashion?
> Or is it going out of the amp on the positive of negative leads?
> (You'll need a scope, and maybe a little antenna)


Not sure. I will have to check.


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## minbari (Mar 3, 2011)

Omicron said:


> Thanks. I will see what I can come up with for a cage.


You can make an enclosed amp rack , just line it with wire mesh

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## nadams5755 (Jun 8, 2012)

The shark fin antennas are for gps and satellite radio. The old aerial/whip antennas for am/fm are now generally vertical lines in the windshield or rear window. 

That said, try to move the amps away from the antennas.


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## 6262ms3 (Feb 27, 2008)

Interesting, in my Mazdaspeed3 I had a Class D (JL HD900/5) mounted vertically on the side wall of the hatch. My Frontier work truck has a Class D Hertz 5 channel under the driver's seat. Neither have had issues with FM interference, which is good because I'm a broadcast technician and have to do critical listening of radio stations often. I wonder if both were just due to luck of amplifier placement? I hope I don't run into this issue with my GSW.


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## Omicron (Jul 15, 2018)

It’s a Santa Fe and I thought that the shark fin handled FM duties as well. 
What i want to do is something like the below (this is a Santa Fe with Dayton subs; I am going to use (2) Arc Black 10” subs if we can get the box small enough to stay in the same space). So I may need to rethink amp placement.


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## nadams5755 (Jun 8, 2012)

If there’s a mast attached to the shark fin, it’s your am/fm as well.


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## nadams5755 (Jun 8, 2012)

My amps interfere with my radio reception. I tried laying down a wideband esd/rfi blanket over my amps, it improved things but not enough to be worthwhile. 

Next time, I’ll be sure to get ceramic window tint instead of the metalized tint, that should help as well.


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## Holmz (Jul 12, 2017)

nadams5755 said:


> My amps interfere with my radio reception. I tried laying down a wideband esd/rfi blanket over my amps, it improved things but not enough to be worthwhile.
> 
> Next time, I’ll be sure to get ceramic window tint instead of the metalized tint, that should help as well.


Faraday cages are not a binary thing.
The window tint is not a mechanism for the noise, not a way to mitigate it.

A class AB would be easier.


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## minbari (Mar 3, 2011)

nadams5755 said:


> My amps interfere with my radio reception. I tried laying down a wideband esd/rfi blanket over my amps, it improved things but not enough to be worthwhile.
> 
> Next time, I’ll be sure to get ceramic window tint instead of the metalized tint, that should help as well.


An esd mat is a capacitively coupled static dissipation mat, NOT a faraday cage. Not surprised that did nearly nothing.

If you put a true faraday cage around it, and the rf is being generated by the amplifier. It will stop. Has to

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## Holmz (Jul 12, 2017)

minbari said:


> An esd mat is a capacitively coupled static dissipation mat, NOT a faraday cage. Not surprised that did nearly nothing.
> 
> If you put a *true faraday cage* around it, and the rf is being generated by the amplifier. It will stop. Has to


I agree that the magic ESD mat is not a solution to a non-imaginary problem.


1) What is a *true* faraday cage?
- If it is a solid silver thing, then that is different than some screen cage.

2) even if the amps are boxed in a silver sarcophagus, then if the power or ground are carrying the offending noise then it is either on the chassis itself, or will be radiated into the air by the power and ground.

But it sounds like people are sure that the mechanism is RF propagation.


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## minbari (Mar 3, 2011)

Holmz said:


> I agree that the magic ESD mat is not a solution to a non-imaginary problem.
> 
> 
> 1) What is a *true* faraday cage?
> ...


A faraday cage id just a wire mesh that completely surounds the object. (Could be solid metal too, but doesn't have to be)

Only requirement is that the mesh be small enough to block the signal in question. 1/4 wave at least if memory serves. It does not have to be anything exotic (like silver) just has to be ferrous

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## nadams5755 (Jun 8, 2012)

Holmz said:


> The window tint is not a mechanism for the noise, not a way to mitigate it.
> 
> A class AB would be easier.


true, but metalized film does impact radio reception, my antennas are in the rear glass. sort of besides the point, suppose i shouldn't have brought it up in this conversation.

if i compare how much i listen to the radio vs using my hatch, i'll stick w/ class-d amps. i like my cargo space much more than radio reception.


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## Holmz (Jul 12, 2017)

minbari said:


> A faraday cage id just a wire mesh that completely surounds the object. (Could be solid metal too, but doesn't have to be)
> 
> Only requirement is that the mesh be small enough to block the signal in question. 1/4 wave at least if memory serves. It does not have to be anything exotic (like silver) just has to be ferrous


I think it is 1/10th, but that is more like a 3dB or 10dB point and there is leakage. Sort of like the comparison between fishnets and chastity belts.

What really happens when a wave hits the conductive surface?

The surface develops currents on it to make the electric field zero at the surface. So the incoming wave gets turned into currents, and those currents rebroadcast an outgoing wave outwards. It is not the same wave, but it is identical to it in every aspect.

For the class D, one would want to keep that EM energy into the AMP's box. Letting the cat out of the box, is a problem... so knowing how it is getting out is probably the best place to start.


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## minbari (Mar 3, 2011)

Ya but most amplifiers are housed in aluminum. Not effective as means to stop rf

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## Omicron (Jul 15, 2018)

minbari said:


> A faraday cage id just a wire mesh that completely surounds the object. (Could be solid metal too, but doesn't have to be)
> 
> Only requirement is that the mesh be small enough to block the signal in question. 1/4 wave at least if memory serves. It does not have to be anything exotic (like silver) just has to be ferrous
> 
> Sent from my LG-LS998 using Tapatalk


I was wondering about density of the mesh material. My original idea was to have the amps visible, but now I am thinking of just having a tunnel-like rack where I can have air-flow directed with some Noctua PC fans (they are low decibel, good flow). And then use dense material to surround the area.


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## Holmz (Jul 12, 2017)

If the amp is encased in aluminum then how if the RF getting out?

Making cages sort of ignores the mechanism of how the RF is escaping... and if it is coming out on the power or ground then a choke will work better than a cage.


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## Omicron (Jul 15, 2018)

Hmm, no go on moving the direction. I will have to have the power and grounds checked to see if it causing the issues. I am half tempted to just move to AB amps, but I don’t think I can power-provide what I would like to with regular alternator/battery setup. With the power I would want from AB, I am guessing 2nd battery and/or bigger alternator?


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## Holmz (Jul 12, 2017)

Omicron said:


> Hmm, no go on moving the direction. I will have to have the power and grounds checked to see if it causing the issues. I am half tempted to just move to AB amps, but I don’t think I can power-provide what I would like to with regular alternator/battery setup. With the power I would want from AB, I am guessing 2nd battery and/or bigger alternator?


What SPL do your run?
What amount of power do you think you need?
Do all Class-D emitter RF interference?


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## Omicron (Jul 15, 2018)

Holmz said:


> What SPL do your run?
> What amount of power do you think you need?
> Do all Class-D emitter RF interference?


Honestly, I don’t know on the SPL angle. Right now, the setup is (4) 6.5” Arc Black mids, (2) Arc Black tweets and for now a Pioneer IB-Flat 10”. The Pioneer is going to be replaced with (2) Arc Black 10” subs. I have an XDi 850.5 (just the sub channel used right now) feeding the Pioneer sub at 2ohm and then an XDi 1200.6 feeding 1 channel to each of the separates. PS8 for DSP duties. The XDi 850.5 will need replaced (with an 1100.1) as that 850.5 won’t drive (2) 10’s adequately in a sealed box. I think the power setup above will be fine for what I have installed (and sub change).

After reading quite a bit on here about AB amps, I was considering what might work best for SQ for me. My thought was a Zapco Z150.6 LX for all the mids/tweets and a 400.2 bridged for the subs. But I don’t think I can make that work with the room I have available and the probable power draw/heat (plus I don’t think I would drive the Zapco’s to their efficiencies anyway). Possibly I could go with the new Arc series class D amps that will have software to mitigate interference, but I am not sure when those will be released. Or I could try the G/H class amps.

Ugh, too much for me to think about!


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## Holmz (Jul 12, 2017)

Omicron said:


> Honestly, I don’t know on the SPL angle. Right now, the setup is (4) 6.5” Arc Black mids, (2) Arc Black tweets and for now a Pioneer IB-Flat 10”. The Pioneer is going to be replaced with (2) Arc Black 10” subs. I have an XDi 850.5 (just the sub channel used right now) feeding the Pioneer sub at 2ohm and then an XDi 1200.6 feeding 1 channel to each of the separates. PS8 for DSP duties. The XDi 850.5 will need replaced (with an 1100.1) as that 850.5 won’t drive (2) 10’s adequately in a sealed box. I think the power setup above will be fine for what I have installed (and sub change).
> 
> After reading quite a bit on here about AB amps, I was considering what might work best for SQ for me. My thought was a Zapco Z150.6 LX for all the mids/tweets and a 400.2 bridged for the subs. But I don’t think I can make that work with the room I have available and the probable power draw/heat (plus I don’t think I would drive the Zapco’s to their efficiencies anyway). Possibly I could go with the new Arc series class D amps that will have software to mitigate interference, but I am not sure when those will be released. Or I could try the G/H class amps.
> 
> Ugh, too much for me to think about!


https://www.amazon.com/BAFX-ProductsÂ-Decibel-Reader-Battery/dp/B00ECCZWWI?ref_=fsclp_pl_dp_1

Well if we start with something we know, then it is easier to peak factually.

We can extend this to the concept of understanding how the Rf interference is happening. (For a instance aluminium is a conductor and also shields electrically fields.) And then whether you need to change to an AB or a different d or something else.
Right now we have solutions to problems which may not be your problems.


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## Omicron (Jul 15, 2018)

Holmz said:


> https://www.amazon.com/BAFX-ProductsÂ-Decibel-Reader-Battery/dp/B00ECCZWWI?ref_=fsclp_pl_dp_1
> 
> Well if we start with something we know, then it is easier to peak factually.
> 
> ...


Thanks. I will grab one of those devices and test it out.


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## Omicron (Jul 15, 2018)

Well, just twisting the amps 90 degrees did not do the trick (new power and grounds were run as well just in case), so we moved them away from the left side of the vehicle (guessing that might be where the booster is for the shark fin). If the vehicle sits still, there is no FM interference. If it moves in a straight line, there is no interference. However, if I turn left or slight right (only those movements), it generates interference. The antennna is solidly plugged in, so I have to wonder if the booster for the shark fin has something touching or loose. That could be why the inference only shows on a turn.


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## dcfis (Sep 9, 2016)

My class d is mounted right above the fin booster and maybe it's because i got it mounted to a cutting board covered in cld tile? Maybe if you got a square lay it on top of the amp


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