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I installed my JL hd 900/5. And now I have poor radio reception now, what can I do. I asked on national vette forum about the location of the stock antenna etc. and 3 of 4 post so far say the amp is the cause ! ??? I have the amp mounted in the back of the 07 vette under the rear window on the back wall of the car. I made a cool mount that looks like its floating and put a fan into it to help keep the amp cool here in the summers ( AZ) . I bought a new sub enclosure too and all sounds pretty good, I have a small engine whine but need to move my rcas away further from the power wire i think. I had 2 a/b amps before in the same area , no problem. I assume ;) that the amp being digital is the issue, but now what ?? fwiw I didn't run any new wires etc, or touch the HU at all. Just installed in the same spot as the a/b amps I had.

thx guys for all the info given to me over the past few yrs.
 

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I cant beleive that an amplifier would cause poor radio reception. those two things are isolated and unrelated. does your ant run near any of the power wires for the amplifier?

and the amplifier is NOT digital. that is not what Class D stands for.
 

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You're the second person i've heard complain about this. There's a little about it in the HD vs XD thread.
 

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I cant beleive that an amplifier would cause poor radio reception. those two things are isolated and unrelated. does your ant run near any of the power wires for the amplifier?

and the amplifier is NOT digital. that is not what Class D stands for.
Last time I checked, switching power supplies are capable of spewing EMI if not designed correctly, or in certain cases of workmanship defects (I test for this kind of stuff at my job). If radiated or conducted emissions happen to be in the am or fm radio frequency range, yes you can get interference.
 

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You're the second person i've heard complain about this. There's a little about it in the HD vs XD thread.
I wonder if the pilot signal in the amplifier is near the LO in the radio.
 

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If you're FM antenna is built into the rear window like many new cars and you amplifier is too close it can absolutely destroy your reception. Don't ask me why or how, but I've seen this problem before and relocating the amp corrected it.
 

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I've read up on this a while back that the older slash series class d amps will cause radio reception problems. Had it happen accross three different cars with the same amp
 

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I cant beleive that an amplifier would cause poor radio reception. those two things are isolated and unrelated. does your ant run near any of the power wires for the amplifier?and the amplifier is NOT digital. that is not what Class D stands for.

What is a Class D Amplifier?
A class D amplifier is an efficient form of switching amplifier. Class D amplifiers switch at a frequency much higher than the audio band. Most Class D amplifiers switch from about 300kHz to 2MHz. It can be up to 90% power efficient, however, it generates more electrical interference than other configurations of amplifier.


Tends in Class D amplifiers.
One problem That has plagued system designers since the introduction of class D is the high amounts of radiated EMI, due to the rail-to-rail switching nature of the amplifier.
http://www.cirrus.com/en/pubs/whitePaper/Trends_in_class_D_amplifiers.pdf

Taming the Class-D for automotive
EMI caused by switching is one of the most important Class-D problems and a very difficult one to solve. At the design level, EMI can be mitigated by phase staggering, frequency hopping, and AD/BD modulation.
http://www.nxp.com/wcm_documents/news/download-media/publications/car_audio_challenge.pdf



Reduce EMI from Class D Amplifiers Using New Modulation Techniques and Filter Architectures
The second factor to affect use of Class D is the technology itself. Driven by market needs, several manufacturers now offer improved Class D technology with costs more equitable and audio performance on a par with Class AB. Some novel Class D output modulation schemes, moreover, now ease the EMI burden in many applications.

Some of the newer Class D designs, although derived from older PWM-style architectures, incorporate sophisticated modulation techniques that achieve filterless operation for lower power systems. Efficiency claims can be verified on the bench, but some designers suspect that products based on these new techniques will be rife with EMC/RFI compatibility problems. In reality, the use of effective PCB layouts and short runs of speaker cable can ensure sufficiently low radiated EMI to pass the applicable FCC or CE standards.

Application Challenges
The physical layout in some applications necessitates long speaker cables, for which RF emissions must be more tightly controlled because the speaker cables act as antennae. In effect, the longer the speaker cable, the lower the frequency at which it acts efficiently as an antenna. Meanwhile, other applications require EMI emissions below that of CE/FCC, perhaps to meet automotive specifications or where interference with other circuitry at lower frequencies must be avoided. With such disparate requirements, these applications were historically difficult to overcome. http://www.maxim-ic.com/app-notes/index.mvp/id/3878



How Class D audio amplifiers work
EMI in Class D Amplifiers
EMI (Electro-Magnetic Interference) in Class D amplifier design is troublesome like in other switching applications. One of the major sources of EMI comes from the reverse recovery charge of the MOSFET body diode flowing from the top rail to the bottom, similar to the shoot-through current. During the dead-time inserted to prevent shoot through current, the inductor current in the output LPF turns on the body diode. In the next phase when the other side of the MOSFET starts to turn on at the end of the dead-time, the body diode stays in a conducting state unless the stored minority carrier is fully discharged. This reverse recovery current tends to have a sharp spiky shape and leads to unwanted ringing from stray inductances in PCB traces and the package. Therefore, PCB layout is crucial for both ruggedness of the design and reduction of EMI.

Conclusion
Highly efficient Class D amplifiers now provide performance similar to conventional Class AB amplifiers if key components are carefully selected and the layout takes into account the subtle, yet significant impact of parasitic components. Greater efficiency, increased power density and better audio performance are driving the increased use of Class D amplifiers with even more improvements on the horizon. http://www.eetimes.com/design/audio-design/4015727/How-Class-D-audio-amplifiers-work


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I'm sure JL Audio has addresses the EMI issue with filtering and sheilding given the work and technology they put in to get these amps sounding good with great THD numbers. But, I am sure it's not totally unavoidable.
 

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What is a Class D Amplifier?
A class D amplifier is an efficient form of switching amplifier. Class D amplifiers switch at a frequency much higher than the audio band. Most Class D amplifiers switch from about 300kHz to 2MHz. It can be up to 90% power efficient, however, it generates more electrical interference than other configurations of amplifier.


Tends in Class D amplifiers.
One problem That has plagued system designers since the introduction of class D is the high amounts of radiated EMI, due to the rail-to-rail switching nature of the amplifier.
http://www.cirrus.com/en/pubs/whitePaper/Trends_in_class_D_amplifiers.pdf

Taming the Class-D for automotive
EMI caused by switching is one of the most important Class-D problems and a very difficult one to solve. At the design level, EMI can be mitigated by phase staggering, frequency hopping, and AD/BD modulation.
http://www.nxp.com/wcm_documents/news/download-media/publications/car_audio_challenge.pdf



Reduce EMI from Class D Amplifiers Using New Modulation Techniques and Filter Architectures
The second factor to affect use of Class D is the technology itself. Driven by market needs, several manufacturers now offer improved Class D technology with costs more equitable and audio performance on a par with Class AB. Some novel Class D output modulation schemes, moreover, now ease the EMI burden in many applications.

Some of the newer Class D designs, although derived from older PWM-style architectures, incorporate sophisticated modulation techniques that achieve filterless operation for lower power systems. Efficiency claims can be verified on the bench, but some designers suspect that products based on these new techniques will be rife with EMC/RFI compatibility problems. In reality, the use of effective PCB layouts and short runs of speaker cable can ensure sufficiently low radiated EMI to pass the applicable FCC or CE standards.

Application Challenges
The physical layout in some applications necessitates long speaker cables, for which RF emissions must be more tightly controlled because the speaker cables act as antennae. In effect, the longer the speaker cable, the lower the frequency at which it acts efficiently as an antenna. Meanwhile, other applications require EMI emissions below that of CE/FCC, perhaps to meet automotive specifications or where interference with other circuitry at lower frequencies must be avoided. With such disparate requirements, these applications were historically difficult to overcome. http://www.maxim-ic.com/app-notes/index.mvp/id/3878



How Class D audio amplifiers work
EMI in Class D Amplifiers
EMI (Electro-Magnetic Interference) in Class D amplifier design is troublesome like in other switching applications. One of the major sources of EMI comes from the reverse recovery charge of the MOSFET body diode flowing from the top rail to the bottom, similar to the shoot-through current. During the dead-time inserted to prevent shoot through current, the inductor current in the output LPF turns on the body diode. In the next phase when the other side of the MOSFET starts to turn on at the end of the dead-time, the body diode stays in a conducting state unless the stored minority carrier is fully discharged. This reverse recovery current tends to have a sharp spiky shape and leads to unwanted ringing from stray inductances in PCB traces and the package. Therefore, PCB layout is crucial for both ruggedness of the design and reduction of EMI.

Conclusion
Highly efficient Class D amplifiers now provide performance similar to conventional Class AB amplifiers if key components are carefully selected and the layout takes into account the subtle, yet significant impact of parasitic components. Greater efficiency, increased power density and better audio performance are driving the increased use of Class D amplifiers with even more improvements on the horizon. http://www.eetimes.com/design/audio-design/4015727/How-Class-D-audio-amplifiers-work


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I'm sure JL Audio has addresses the EMI issue with filtering and sheilding given the work and technology they put in to get these amps sounding good with great THD numbers. But, I am sure it's not totally unavoidable.
^^^^ Exactly what he said.

/thread
 

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I have an HD and an XD both in my trunk, and my radio reception is almost non existing. My antenna is in my rear window also and ever since those amps were mounted, I've had no radio reception. :(
 

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I had one of my HDs in the trunk for a day or two before I could get around to mounting it under the seat. I don't think I attempted to listen to the radio although I wish I did now. No issues with two of them under the seats.
 

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This makes me think that both amps need to be mounted under the seats and the MS8 in the trunk.
 

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JL tech will confirm that the HD amps can cause poor reception or noise on the tuner. Many Rockford amps will do the same.
 

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Any thoughts as to reduce the effects of this besides changing amps?
 

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Hi,
Change the amp. Did a HD900/5 on a harley trike...no reception, switched to an Alpine pdx5...usable reception. Of course, the antenna was just several feet away from the amplifier which was mounted in the lower trunk...fiberglass. Copper wire mesh shield around amp did nothing.
mark
 

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Dang so my choices are dump the amp that I love, or run straight satellite. I'm going the satellite route, FM radio is over rated to begin with lol.
 
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