Class D Technology

atmasphere,

     Good points about class D amps being immune from noise due to their modules or the  smps but that  RF radiated noise could be a problem for other equipment nearby and even pacemakers and other electronics either within or separate from one's system.   I was warned of possible RF radiation about the same time I purchased my first D amp.  

     I read a tip that a portable am/fm radio could be used as a crude detector for any RF radiation emitted by a component. The instructions were to tune to a spot on the dial that is between stations that is relatively quiet,  turn the volume control to about 3/4 and  move the portable radio slowly around all sides of the tested component.  The point being that if the component is radiating any RF signals/interference it will be indicated by the portable radio producing a change in sound once it is in the proximity of  any component being checked.  I did this test on my D amps on the am and pm bands (since the tipster didn't specify a specific band) and I noticed no changes in sound coming from the portable radio but I hope this was a valid method for RF radiation detection.  

     Seanheis1 stated:

" Maybe we will start seeing Class D pre-amps then... "

  My understanding is that class D pre-amps would not have  any significant advantages over traditional tubed and ss pre-amps,  that I believe all operate in class A.  This is mainly due to the signal amplification being so small in class A  pre-amps  that heat and energy efficiency are not significant issues as they are in tubed,class A and class A/B amps.  

Tim   

I read a tip that a portable am/fm radio could be used as a crude detector for any RF radiation emitted by a component.

Yes for smps leakage, should also work not that I tied it for Class-D switching frequency leakage.
Tune down low and try at different frequencies between 500-800khz on the am/band, so it’s off station not getting a station signal just white noise (some portables mute these are no good to use), then switch on the smps/class-d, and go close to it with the radio, and see if you get a change in sound or level.

Cheers George

georgelofi,

     Thank you for the further clarification.  I just tried your suggestion  with an older (non-muting) portable radio in the 500-800 khz am/band range on my amps with results being no discernible change in sound.or level.  Reassuring results.

Thanks again,
  Tim

There is about 1% of switching voltage noise on the speaker cable since filter is not perfect but, as I said before, 1/300 wavelength antenna won't radiate.  In addition, electricity in speaker cable flows in both directions canceling the most of RF (if any).  When you place radio directly on the wire you might get some capacitive coupling, but I doubt it.  Many speaker cables are twisted making it completely inefective (better than shield) for electromagnetic radiation or capacitive coupling (both ways - from cable or to cable).