Class D: Turns Out it Does Suck!

[wgscott]

[wgscott]

19 hours ago, esldude said:

They didn't blow much of the budget on beautiful build quality either. Kept it where it counts....producing the kind of special distortion people crave. 

 

 

 

 

That really is horrifically ugly.

 

 

 

 

 

 

 

[wgscott]

31 minutes ago, monteverdi said:

one thing I have not seen discussed here is the environmental impact of different amp designs

 

That was one of my primary motivations for trying Class D.  I am trying to produce more electricity that we consume. 

 

We also have a serious ecological catastrophe unfolding ...

 

Even if the inferior sound quality allegation amounts to anything more than snobbery, I think I could live with the very minor difference, given the difference in power consumption.

[wgscott]

4 hours ago, watercourse said:

 

I have my Pass situated right next to the intake vent for my heat pump (this is necessary during the warm summers). Too bad the intake is on the floor and heat rises. If I install ceiling fans, my heat pump system becomes less efficient by virtue of increased energy consumption.

Anyone at CA have a system that stores energy generated by stationary bike? Have owned several Class D amps and am not budging from Class A now that I've tasted the honey. I clearly need some carbon offsets to maintain this habit.

 

Get a few solar panels.

[wgscott]

Here are some really compelling measurements of the Hypex NC-400 DIY amp, and interestingly, a few others added in

 

https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-hypex-nc400-diy-amp.5907/

 

The NC-400 is substantially better than NuForce STA-200, for example.

[wgscott]

I am so happy I don't need to colorize the signal while amplifying it in order to enjoy music.

 

(The neutrality of an amp is normally considered to be an asset.)

[wgscott]

My tweeters (not to mention my hearing) cut out above about 22 kHz, so a 460kHz signal isn't keeping the dogs up all night.

 

[wgscott]

Why would it be applied to the tweeter?

 

Even so-called ribbon super-tweeters only respond to 80kHz or so.

 

http://www.enjoythemusic.com/magazine/equipment/0106/tonian_tlr1.htm

 

 

[wgscott]

Are you seriously worried about a 460kHz spike that is -75dB relative to the test signal?

 

 

[wgscott]

6 minutes ago, sandyk said:

 

 Richard is saying it is actually -15dB , NOT -75dB.

The filter being used for measurements has attenuated the switching frequency by 60dB., unless I have misunderstood what he is saying.

 

I may have mis-understood too, but even if it is not attenuated at all, no speakers that I have ever seen (let alone mine or anything else commercially available) will see that frequency, let alone respond to it.

 

As for interfering with AM radio, the US and EU have rather strict laws regulating electronics, as I am sure Australia has to. (Given the ubiquity of class-D amps in all sorts of non-audiophile contexts, if this was a real problem, it would have emerged by now.) Often amplifiers are enclosed in metal boxes.  Mine isn't, and creates no such problem.  But given all the right-wing drivel on AM radio, this gives me an idea for a new audio startup ... I'll call it "Jamming to Class D".

[wgscott]

13 minutes ago, sandyk said:

 

That's not the point. The leads to the tweeters will also be radiating this crud, as will the tweeters themselves.

 That is also part of the reason for a Fan Filter in a PC ,as the windings of the fans will also radiate the harmonics of the basic 25kHZ motherboard controlled PWM used to control the fan speed.

 Neither can it be helpful for a tweeter to be vibrating at 460kHZ while attempting to faithfully reproduce other frequencies in it's intended response range.

 

You guys must love DSD

[wgscott]

27 minutes ago, diecaster said:

 

What do you have against DSD? Most of my music is Redbook but the DSD I do have sounds great on my 2 channel setup.  

 

Nothing, really.  But has a big noise hump that starts around 50kHz or so.

 

Presumably your system, like mine, is unaffected by that frequency.

 

Neither my ears, my speakers or my dogs are sensitive to this.

 

[wgscott]

11 minutes ago, diecaster said:

 

That would not make any sense. There is a big difference between moving noise way up in the frequency range and having an amp that pumps out high frequency noise. 

 

What difference does it make, from the point of view of the speakers (and listener)?

[wgscott]

11 hours ago, Shadders said:

 

Again, if both class A/B and class D amplifiers have the same THD profile from 20Hz to 20kHz using the 22kHz measurement bandwidth, then why are they reported to sound different ???, and class D all sound similar ???

 

Price tag.

[wgscott]

Why would you get that rather than an NC-400 kit?

[wgscott]

The 460kHz output is simply a non-issue.

 

Many of us have lived with this for years, if not decades.  

 

The FCC prohibits the sale of electronic devices that interfere with radio signals.  

 

Most people (including me) struggle to hear any output from their tweeters at all, so even in the unlikely event than any of what you are saying is a realistic concern for the tweeter, I still am not buying that it makes any difference at all.

 

If it did, it would be a very simple to put in a filter at the output stage to correct the problem.  

[wgscott]

12 minutes ago, psjug said:

So the question is whether this is a problem or not.  I don't think it is unreasonable for some to reject Class D because of this.  Here is what Hypex/BP has to say on the subject:

 https://www.hypex.nl/img/upload/doc/an_wp/AN_UcD_and_EMI.pdf

 

 

Thanks for the link.  That should give SandyK the answer he wants (as well as Shadders, hopefully).

 

[wgscott]

8 minutes ago, Shadders said:

Hi,

To add definitive numbers to the theory, i used the Elektor Class D amplifier (Jan 2017) which has a 22uH and 470nF second order filter, and simulated the +/-70volts switching voltage into a 6ohm resistor.

 

The following is the ac analysis :

 

The difference between the output voltage in the audio band and the filtered signal at 450kHz is 38.2dB. This then correlates to +/-0.88volts applied to the tweeter at 450kHz.

 

This is not insignificant. It will in general be the same as frequencies at the tweeter frequencies of 2.5kHz, but significantly more than the energies at the frequencies 10kHz to 20kHz. Every class D amplifier will have this signal permanently applied to the tweeter.

 

Regards,

Shadders.

 

What is the tweeter impedance at that frequency?

[wgscott]

Is there anything in the following that is problematic?

 

 

[wgscott]

11 minutes ago, Shadders said:

The concern is the effect of stimulating the tweeter at 450kHz with 0.88volts peak to peak, upon the tweeter operation when it is reproducing the audio range 2.5kHz to 20kHz (example).

 

Apologies for not following, but if that doesn't manifest itself as intermodular distortion, how does it impact the sound?

 

I have a set of Class D amps that are inferior to the NC-400, and I have seen no evidence of this issue.  (I was also loaned a pair of NC-400 by a generous member of CA, and didn't notice a difference at the high frequencies.  I suspect mine have the inferior filtering.)

 

@sandykMany cheap AM/FM receivers have inferior Class D amps, yet they manage to receive these radio signals unscathed.  How can that be?

[wgscott]

@Jud  While you are at it, can you show me a link that proves Steven King did not kill John Lennon?

[wgscott]

28 minutes ago, Shadders said:

Hi,

If you read my original statement, it was a question whether this carrier frequency is the cause of all class D amplifiers sounding the same.

 

Regards,

Shadders.

 

How often do you beat your children?

 

Ideal amplifiers should all sound the same.  Maybe all Class D amplifiers are closest to ideal?  (I don't personally believe they are, but that would be the simplest and most logical conclusion, assuming the accuracy of your premise.)

[wgscott]

Just now, Jud said:

 

You stated the tweeter diaphragm has to move, Putzeys says it doesn't. So we have a choice of two diametrically contradictory explanations.

 

In fairness, his claim is that it damages the sound quality, by placing a signal that oscillates at 460 kHz on the tweeter, and he has also ruled out intermodular distortion.

 

He never discounted audiophile magic bad karma fields.

[wgscott]

So, again, what is the problem?

 

Why is EMF that causes no issue a bigger concern than massive energy consumption and heat radiation from Class A?

 

Each "topology" has its strengths and weaknesses.

 

As long as the weaknesses are inaudible (or nearly so), I am quite happy to have boxes in my living room that aren't room/planet heaters.

 

 

[wgscott]

2 minutes ago, Shadders said:

Hi,

I have referred to the Hypex article as per others. Hypex claim that there is no intermodulation. I have not claimed there is, or there is not, intermodulation issues in regards to the diaphragm. Hypex actually state "and the only signals around for the carrier to intermodulate with are its sidebands." These are due to the class D signal.

 

Regards,

Shadders.

 

Let's assume you and GUTB are right and the Hypex engineers are wrong. Class D sucks, and you have elucidated why this is.

 

What is the physical mechanism by which the 460kHz input degrades sound quality?