[Audiovista]

As follow-ups please: In the emission frequency range you specified, can you say approximately what amount of EMI your amps (and to your knowledge, other manufacturers' switching amps) actually do emit?  Is there any possibility (even remote) of any health impact or danger, from long term exposure to these emissions at close ranges?

Tommy will answer for his products specifically - I'll just post some general info...

Class D amplifiers, along with ANY electronic component having oscillator operating above 9kHz, MUST comply with FCC imposed emission limits in the frequency range of 450kHz to 1GHz (450kHz to 30MHz for conducted emissions and 30MHz-1GHz for radiated emissions). In Europe, limit is 150kHz-1GHz (and 30MHz is a crossover between conducted and radiated emissions). This is for UNINTENDED radiators, not for radio stations, cell phones, etc. In practice, most switchmode power supplies and class D amps radiate in 100kHz-150MHz range.

The actual limits for household equipment are more stringent than for industrial equipment.

Now - the primary goal of the regulations is to prevent harmful effects on other electronic equipment (in Europe the equipment must have a certain level of immunity to electrical and magnetic fields). I am not aware of any regulation or study discussing harmful effects on humans. However, allowed emission levels are much lower than your typical cordless or cell phone, wireless router, etc.

Boris

[AmpDesigner333]

As follow-ups please: In the emission frequency range you specified, can you say approximately what amount of EMI your amps (and to your knowledge, other manufacturers' switching amps) actually do emit?  Is there any possibility (even remote) of any health impact or danger, from long term exposure to these emissions at close ranges?

Tommy will answer for his products specifically - I'll just post some general info...

Class D amplifiers, along with ANY electronic component having oscillator operating above 9kHz, MUST comply with FCC imposed emission limits in the frequency range of 450kHz to 1GHz (450kHz to 30MHz for conducted emissions and 30MHz-1GHz for radiated emissions). In Europe, limit is 150kHz-1GHz (and 30MHz is a crossover between conducted and radiated emissions). This is for UNINTENDED radiators, not for radio stations, cell phones, etc. In practice, most switchmode power supplies and class D amps radiate in 100kHz-150MHz range.

The actual limits for household equipment are more stringent than for industrial equipment.

Now - the primary goal of the regulations is to prevent harmful effects on other electronic equipment (in Europe the equipment must have a certain level of immunity to electrical and magnetic fields). I am not aware of any regulation or study discussing harmful effects on humans. However, allowed emission levels are much lower than your typical cordless or cell phone, wireless router, etc.

Boris

Boris,

Thanks very much for your post.

Regarding the effects of low level EMI on organic matter (like, people), I'd also like to know more about this.  As far as the magnitude of various sources, AC power lines are on the top of the list, even though the frequencies are low.  Next comes your cell phone.  Didn't US courts throw out a bunch of cell phone radiation related cases in the 1990s?

BTW, I'll get to the UCD question soon...

BR,
Tommy

[AmpDesigner333]

Hey, folks...
We received a Cherry last week that was dropped, so the faceplate was sheered off and the chassis suffered some minor bend and paint chipping.  I plan to fix this up with new boards.  If you are interested in this unit, please send an email to Support@DigitalAmp.com.  Thanks.

Tommy

[AmpDesigner333]

And since I've already blapped more than I should I can tell you guys that he is intimately familiar with the operation of the UcD and ICE modules, and feels absolutely confidant that his designs are superior in both theory and implementation.

Would very much like to hear how exactly his designs better the UcD in theory and implementation....

There are a few key differences.  For one, UCD takes feedback after the filter which allows less phase margin and relies on the capacitance of the output to control the modulation.  There is also more than a decade of R&D behind the Digital Amp Co. methods involving much more than the general topology of the amp.  We use innovation in our modulation method, component selection, and practical implementation matters (layout, partitioning, etc.).

Sorry this can't go to the "exactly" level without divulging some "secret sauce" info.  We believe UCD is one of our more worthy competitors, and we have the greatest respect for Bruno P who created the technology.  I'd like to hear some more opinions from people who have heard both, preferably in an A/B comparison.  So far, we have heard that the Cherry and DAC4800A sound better all around, but keep in mind the speakers, source, power output, and setup can make all the difference.

Thanks for your post!

[NewBuyer]

...AC power lines are on the top of the list, even though the frequencies are low.  Next comes your cell phone...

Thanks Tommy and Boris for the info regarding the type/frequencies of radiation that these switching amps emit. 

Tommy, just to reiterate my above question please: In the emission frequency range you specified for your amps, have you measured and can you say (approximately) what amount of EMI radiation your amps actually do emit? 

[AmpDesigner333]

...AC power lines are on the top of the list, even though the frequencies are low.  Next comes your cell phone...

Thanks Tommy and Boris for the info regarding the radiation type/frequencies that these switching amps emit. 

Tommy, just to reiterate my above question please: In the emission frequency range you specified for your amps, can you say approximately what amount of EMI radiation your amps actually do emit?

I can't show plots due to an NDA with a customer.  The emissions are low with respect to other amplifier designs.  Do you know of any companies that publish their EMI test results?  Thanks again.

[NewBuyer]

I can't show plots due to an NDA with a customer.  The emissions are low with respect to other amplifier designs...

No plots is fine... could you at least say please what the max values are, that your amps ever emit?

[satfrat]

I can't show plots due to an NDA with a customer.  The emissions are low with respect to other amplifier designs...

No plots is fine... could you at least say please what the max values are, that your amps ever emit?

Newbuyer, can you enlighten me to any other company that publishes the type of info that you're asking Tommy to do? Thanks.




Cheers,
Robin

[AmpDesigner333]

I can't show plots due to an NDA with a customer.  The emissions are low with respect to other amplifier designs...

No plots is fine... could you at least say please what the max values are, that your amps ever emit?

I'll send you an answer via PM...  Thanks again.

[NewBuyer]

I can't show plots due to an NDA with a customer.  The emissions are low with respect to other amplifier designs...

No plots is fine... could you at least say please what the max values are, that your amps ever emit?

I'll send you an answer via PM...  Thanks again.

Hi Tommy,

Good to know - I appreciate your fast PM regarding this radiation information.  I sense you may not be comfortable making this information public, so I won't repeat it here (I hope others will please understand).  My thanks again for your replies and help.

[cab]

There are a few key differences.  For one, UCD takes feedback after the filter which allows less phase margin and relies on the capacitance of the output to control the modulation.  There is also more than a decade of R&D behind the Digital Amp Co. methods involving much more than the general topology of the amp.  We use innovation in our modulation method, component selection, and practical implementation matters (layout, partitioning, etc.).

Sorry this can't go to the "exactly" level without divulging some "secret sauce" info.  We believe UCD is one of our more worthy competitors, and we have the greatest respect for Bruno P who created the technology.  I'd like to hear some more opinions from people who have heard both, preferably in an A/B comparison.  So far, we have heard that the Cherry and DAC4800A sound better all around, but keep in mind the speakers, source, power output, and setup can make all the difference.

Thanks for your post!

The Ucd uses feedback, your amp doesn't, we know that. Why is yours better from a theoretical standpoint? I am guessing the UcD has much better distortion specs, which in theory, should make it superior.

10 years of time developing your amp means nothing as far as why it is superior from a theoretical or implementation standpoint.

You seem reluctant to discuss EMI data on your amp... Has it passed the EU requirements for radiated EMF? What makes your layout, etc., better? UcD is well known to have passed and has very little EMI, unlike most other class d amps....

No offense, but Bruno, based on his work, publications, and patents, is recognized as one of the leading authorities, if not the authority, in the world, on class d amp design. Other than this amp, what publications, patents, and research have you published which would lend credence to your claims that you have out designed and out implemented the leading expert on class d?

To say that some people think it sounds better is not proof in my book-too subjective and too dependent on a multitude of other factors...besides, I am sure there are plenty of people who would disagree...such is the subjective nature of audio....

I have no doubt your product is a good one; it simply seems to me that the claims that it is a better design and implementation than the UcD is a bold statement that requires more than hand waving to back up.....

[brj]

The Ucd uses feedback, your amp doesn't, we know that. Why is yours better from a theoretical standpoint? I am guessing the UcD has much better distortion specs, which in theory, should make it superior.

I've never owned a class D amp of any kind (mostly due to a lack of opportunity), but did just read an interesting article by Nelson Pass on negative feedback and the value of distortion specs as currently reported by most manufacturers:

http://www.6moons.com/industryfeatures/distortion/distortion.html

(I certainly wouldn't claim anyone is an authority over anyone else, but Nelson Pass certainly has a lot of experience in this area...)


As a general point, keep in mind that electromagnetic radiation follows an inverse square law, meaning that if you double the distance from the amp, the EM drops by a factor of 4.  Triple the distance, and it drops by a factor of 9, etc..  While I certainly like the idea of minimizing EMI as a general concept and pay attention to such things myself, I focus much more on the cell phone that I hold next to my head rather than components located some distance away from me when operating.

(That said, I'd be curious to see the EMI numbers more generally reported by amp manufacturers as well, if for no other reason than to let me know ahead of time whether I'd be forced to use shielded ICs.)

[jon_010101]

The Ucd uses feedback, your amp doesn't, we know that. Why is yours better from a theoretical standpoint? I am guessing the UcD has much better distortion specs, which in theory, should make it superior.

I think what Tommy is trying to say is that his feedback is taken before the output filter rather than after, not that it doesn't use feedback.  As long as the output filter is of high quality, it will contribute very little distortion of its own.  In tube amplifiers, for example, it is most common to take feedback after the output transformer - but stability gains can be had by taking it before, with comparable distortion-reduction.

Judging by the measurements posted on the website, his amp should have no problem competing with a UcD.  I am mighty impressed, and proud to see it is a product of Pennsylvania

[satfrat]

The Ucd uses feedback, your amp doesn't, we know that. Why is yours better from a theoretical standpoint? I am guessing the UcD has much better distortion specs, which in theory, should make it superior.

I've never owned a class D amp of any kind (mostly due to a lack of opportunity), but did just read an interesting article by Nelson Pass on negative feedback and the value of distortion specs as currently reported by most manufacturers:

http://www.6moons.com/industryfeatures/distortion/distortion.html

(I certainly wouldn't claim anyone is an authority over anyone else, but Nelson Pass certainly has a lot of experience in this area...)


As a general point, keep in mind that electromagnetic radiation follows an inverse square law, meaning that if you double the distance from the amp, the EM drops by a factor of 4.  Triple the distance, and it drops by a factor of 9, etc..  While I certainly like the idea of minimizing EMI as a general concept and pay attention to such things myself, I focus much more on the cell phone that I hold next to my head rather than components located some distance away from me when operating.

(That said, I'd be curious to see the EMI numbers more generally reported by amp manufacturers as well, if for no other reason than to let me know ahead of time whether I'd be forced to use shielded ICs.)

I wholeheartedly agree with your last statement, it would be nice if all companies made available EMI numbers for consumers but I've never seen any myself? I guess neither has Newbuyer has he failed to answer my question on the subject. So Newbuyer, have you presented this same line of questioning to Bryston in their Circle? I've failed to see it mentioned in your recent posts to them but I would like to, if for no other reason than to see what answer you'd get from them?

Alone those the same topic of EMI radiation, I have to wonder how effective Audio Magic Pulse Gen ZX units are in counteracting these emmisions? I use these little gems inside all my components, even my DirecTv HD DVR, HTPC computer and the breakerbox. I had never been concerned or actually even thought about the adverse "human" effects of EMI til Newbuyer brought it up but now I see an even more increased value for these little EMI fighting units than I had previously realized. I wonder what a Pulse Gen ZX would do for a Cherry amp? Hey Tommy, maybe we can find out at a future RAVE possibly, I have a spare I could bring for such an occasion if interested. 


Cheers,
Robin

[cab]

I think what Tommy is trying to say is that his feedback is taken before the output filter rather than after, not that it doesn't use feedback.  As long as the output filter is of high quality, it will contribute very little distortion of its own.  In tube amplifiers, for example, it is most common to take feedback after the output transformer - but stability gains can be had by taking it before, with comparable distortion-reduction.

As long as the output filter is outside the loop, the distortion of the amp will not be load independent. That means it will react and perform differently with varying load impedance. Know any speakers with a perfectly flat impedance?

Usually amps of this design are optimized for a set impedance, which means they are suboptimal at every other impedance. UcD does not have this problem.

Also, amps without post filter feedback usually have difficulty with very low impedance loads. Not sure about these amps-can they handle 1 ohm loads without blinking like the UcD?

[cab]

Here is what I am talking about:

Frequency response vs load:

Cherry Amp (4 and 8 ohm loads):



UcD Amp



The UcD is FLAT for 3, 6 and infinite ohms (open circuit).

One can see that the frequency response for the Cherry varies depending on the load. Figures aren't provided for less than 4 or greater than 8 ohm loads, but the trend is apparent.

[richidoo]

Only class D amps with high switching freqs are a problem for EM pollution. Bryston does not make class D amps.

[brj]

Only class D amps with high switching freqs are a problem for EM pollution.

You do need to distinguish between the power supply and the amp module.

A non-switching amp module could be fed by a switch mode power supply (although I can't think of any shipping amps offhand that use this configuration) while many class D (switching) amps use a linear power supply.  Like anything else, this comes down to a design choice.  Design the amp chassis to be a big Faraday cage, and this becomes far less of a concern - if was a concern to begin with.


CAB, it is entirely possible that Tommy doesn't have the same design philosophy, especially regarding feedback, that UcD does, in which case you wouldn't expect identical specs.  Certainly many amps play better with some types of speakers than others, but work exceedingly well for the subset they target.  (I'd never use a tube amp to drive a demanding woofer, for example, but many people will use nothing but tubes on a sensitive speaker or the mid-tweet of a more demanding speaker - even if tube amp specs aren't always as impressive as the specs of other amp topologies.)  Personally, specs alone wouldn't preclude me from listening to any amp, especially as I'm pretty convinced that the commonly reported measurements don't go far enough in fully characterizing what we can actually hear.  (For example, when people discuss distortion in amps or jitter in sources, I'd like to see the spectra involved, not just a single max value.)

[TomS]

Only class D amps with high switching freqs are a problem for EM pollution.

... although I can't think of any shipping amps offhand that use this configuration) while many class D (switching) amps use a linear power supply.

...

FWIW, NuForce is probably one.  I dont' think they have room or dissapation capability for a linear supply in their little case.

[satfrat]

Only class D amps with high switching freqs are a problem for EM pollution. Bryston does not make class D amps.

Ohh, didn't know that. Thanks for cluing me in.

Cheers,
Robin