Let's stop calling Class D amplifiers "efficient" when they are not.

[restorer-john]

By the time it dies, (if it does) it would have used 50% more energy compared to a comparable power Class D amp.

I doubt that. It's already been functional for 30 years. (I should know, I sold them new). I think I have one somewhere in my HiFi room too.

 

[Deleted member 48726]

It won't die. The MX-630 has so much ventilation and heatsink area it will essentially last forever. (built on the chassis of its bigger brothers, the 830 etc)

I know it won't. I've unknowingly tried to kill it since the nineties. I still have it. It still works.
But it's not a fringe case, many amps are mirrored designs of that one regardless the brand from that era.

 

[Neddy]

No, that's not the issue.

The issue is too much dissipation at idle for all but the Purifi and the new NCX modules. I've tested enough of them to know an NC500 with an appropriate SMPS will be disipating over 20W at idle. Put two in a box and you have 40W.

You might say 40W is nothing. But you'd be wrong. 40W in a unventilated or poorly ventilated box means internal temperatures rise well into the failure mode area. I've just had yet another Hypex based class D stereo NC500 amp on my bench (an early NORD one). It had cooked itself (44W measured at idle), as had the unheatsinked Sparkos 'discrete' regulators and the 'discrete' opamps by Sonic Imagery. All in the trash where they belong. They pull enough current on their own to run hot enough to die. That said, even when running from the onboard SMPS linear regulators and a sensible OPAMP installed, the internal temps are still too high. I've advised the owner to put twin variable speed computer fans on top of the amplifier and not install it in a rack.

The two SMPS transformers on each PSU have components sitting around 85 degrees Celsius when idling and playing nothing- just turned on. The output filters on the NC500s are up to 95 degrees Celsius! That's 203 degrees F. Now you don't need to be Einstein to realize what happens to components sitting up against that sort of heat for the long term. They die.

The heat producing transformers and OPT filters have no ability to get rid of heat effectively. They can't be heatsinked easily. They need forced air cooling. This Nord had ventilation slots in the base, but they were mostly covered by the installation of the SMPS supplies and the only space for air to enter was a 2"x3" uncovered vent space. The entire cabinet is aluminium and the top lid ventilated perforations, but that doesn't matter. Spot temps on particular components are too high.

The other amplifier was also a Class D which pulls 30+ watts at idle with NO ventilation whatsoever. Completely sealed.

The third thing on my bench last week was another heat related issue. But it was a DAC from Benchmark. Again, completely sealed cabinet, pulls 10.2 Watts in operation and gets too hot inside that tiny box. All things from the Northern Hemisphere where it is cold more than it is hot. No good down under and we're not even in summer.

If I wanted a Class D, I'd buy a Purifi implementation from Boxem. His cabinets are ventilated, mounted properly and the modules he uses have the lowest idle losses.

I personally just LOVE how good you are at tossing verbal grenades over the "assumption" wall, and running like hell!
Well done!

And... how well the ASR members respond - in kind (so to speak)...right down to the gimli glider link!

Me? TLDR, mostly, but I have two 8" (nearly dead silent) noctuas running off a temperature sensing controller that keeps my rack at about 80F, and never exceeds 90F, with 10 channels of ampflication. I haven't measured it (I could, easily enough) but I suspect the Venu360 uses more power than the 252 4 chan amp at idle.
I DO know that turning off the entire system when not in use (which I never used to do) has - in part - reduced my typical power bill by 25%!
My response, tho, in general is: "Interesting, but"

 

[Davide]

There is a reason(s) that class D is becoming the norm

Sure, they are convenient in terms of price, size and consumption.
Will their lifespan be sufficient to amortize the energy and resources spent on their development/production/marketing?
With the difference in efficiency compared to a class AB I don't think so.
The truth is that no one will ever really know, and in any case it is not predictable.
Let's say that our opinions are equivalent to bets.

I honestly just hope that my two Hypex last 30 years with the fans and heatsinks I added to them. Outside of the guarantee I always have the risk of €1000 going up in smoke. In all senses.

 

[Bjorn]

Here's something our engineer (of Vera Audio) wrote about class D in regards to temperature and cooling:

I would like to say a little about power and cooling requirements in class D amplifiers since there is a widespread attitude that this is not a problem. Chapter Audio was one of those who underestimated this and sold expensive amplifiers that failed after a relatively short time. (P.S. He has had several he was asked to fix)

If you want to extract high effects from class D, cooling is required. But not in the same way as in traditional class A/B amplifiers, where all the effect is transferred in the transistors that are placed on the heatsink.

Class D amplifiers also have switching transistors that must be cooled. These sit on a cooling plate and it doesn't take much to keep the temperature on these under control. As a rule, it is enough that they are screwed to the chassis.

But at the output there is a coil, which together with capacitors lowers the switching noise to livable levels and there a good deal of heat develops both at idle and especially at high currents. Since class D amplifier modules are typically made physically small, the heat from this coil will in practice heat up the entire module to temperatures that will eventually cause the electrolytic capacitors to dry out.

When we designed the Vera amplifier we had a desire to offer high power and before the cooling solution came into place I measured temperatures of over 120 degrees on the modules! The modules can withstand it, but it goes without saying that they will not last long if they are exposed to such temperatures over time.

He goes on to talk about the cooling solution chosen in Vera Audio P400/1000 and shows temperature measurements, something I think is more appropriate to share in the Vera Audio thread and on our website.

 

[levimax]

It is interesting that as technology advances so does standardization. With Class D there are only a handful of companies that manufacture the modules or IC's so all products are basically the same thing in different boxes. While nothing is preventing better solutions for thermal management of the existing modules and IC's I think it would be interesting if some companies could offer long lived designs with thermal management designed in from the ground up and other companies offering cheaper shorter lived designs and letting the market and consumer decide. Unfortunately that is not going to happen as the economies of scale for the chips and modules make them the only viable solutions and in a way hinders innovation beyond making things cheaper.

 

[DonR]

It is interesting that as technology advances so does standardization. With Class D there are only a handful of companies that manufacture the modules or IC's so all products are basically the same thing in different boxes. While nothing is preventing better solutions for thermal management of the existing modules and IC's I think it would be interesting if some companies could offer long lived designs with thermal management designed in from the ground up and other companies offering cheaper shorter lived designs and letting the market and consumer decide. Unfortunately that is not going to happen as the economies of scale for the chips and modules make them the only viable solutions and in a way hinders innovation beyond making things cheaper.

It is also not the same market as it was 40 years ago. Home audio is now the purview of Alexa and Nest speakers or Bluetooth speakers. Ironically, these also contain Class D amplifiers but of a different breed.

 

[Ricardus]

I agree with this. It's almost like you need two amplifiers in one- a normal, highly efficient, low output power unit for day to day cruising along and a balls-to-the-wall blaster for when you want to rock the house. Many attempts have been made to do this.

Didn't Bob Carver make an attempt at that with her earliest Sunfire designs? I forget what his idea was but I remember reading the hype back in the day.

 

[IAtaman]

I doubt that. It's already been functional for 30 years. (I should know, I sold them new). I think I have one somewhere in my HiFi room too.

Well, to your point, and even beyond thermal considerations, semiconductors manufactured in 80s and 90s would have higher lifetime compared to ultra high density products of today. If that amp was built with modern transistors and ICs I don't think it would last as long.

 

[JayGilb]

He goes on to talk about the cooling solution chosen in Vera Audio P400/1000 and shows temperature measurements, something I think is more appropriate to share in the Vera Audio thread and on our website.

With the popularity of active speakers, would the vibration imparted on the class d modules have much of impact on the lifespan ?

 

[Armand]

With the popularity of active speakers, would the vibration imparted on the class d modules have much of impact on the lifespan ?

A good question. And as always, -I guess it depends. Modern circuit boards with small and light components can withstand a lot of vibration. The output coil is however fairly heavy and it could cause problems if subjected to too much vibration. That being said, these are soldered to the circuit board using many heavy duty soldering points, so in general I would say that no, I don't think this is going to be a huge problem.

 

[IPunchCholla]

Lifetime costs are also substantially impacted by repairability... an old 1980's Quad 606 can be fully refurbished easily and with minimum number of hours labour, and minimal parts costs.... a current generation Class D amp, typically would require replacement of the amp board and all components, rather than repair... the Quad 606 gets a new lease of life after 30+ years with minimal cost, and is ready for another 30 years... the lifetime construction and disposal costs are amortised over many decades...

I am unconvinced that current class D amps such as ICE, Hypex, Purifi etc... can say the same...

Thank you for the reply. That is a good point. Could you put a number on minimal? As in if I had to pay someone to do it? I’m just trying to think through the issue since some of the amps we are talking about are $80.

 

[Deleted member 48726]

Thank you for the reply. That is a good point. Could you put a number on minimal? As in if I had to pay someone to do it? I’m just trying to think through the issue since some of the amps we are talking about are $80.

I'd think minimal would suggest replacing of aging electrolytics and cleaning of potentiometers and switches with adjustments of bias and offset. -A regular.

 

[tmtomh]

I personally just LOVE how good you are at tossing verbal grenades over the "assumption" wall, and running like hell!
Well done!

If you change "LOVE" to "HATE," I agree completely.

Because why have a discussion based on precise explanations and specific empirical data when we can just let @restorer-john keep saying that his favorite amps will last "forever" and that whatever he doesn't like is "bullsh**"?

Okay then. I'll rewind to which class d amps are considered vintage?

The fact is that many a/b amps has already proven to last 30 years and still going and are still able to be repaired if needed.

The question is how many class d amps you would have to recycle and buy in those 30 years time. And which option is better for both the planet and the economy..

As for longevity data on Class D amps, can't some of that be gleaned from car audio amps and the 1970s Sony Class D amps?

And haven't Genelec Class D-based active speakers been out for about 8 years now? Is there any failure data on them compared to failure data on their prior AB-based speakers?

It would be interesting to try to compile data since Class D amplification has been mainstream for quite some time now. Of course that's only if John can restrain himself from constantly redefining what exactly he's so mad about - case size, thermal/cooling designs, Class D module layouts, whatever. I'm pessimistic about his ability or willingness to keep the tantrums in check, and about the willingness of his enablers here to stop indulging him so much.

 

[NoMoFoNo]

Lifetime costs are also substantially impacted by repairability... an old 1980's Quad 606 can be fully refurbished easily and with minimum number of hours labour, and minimal parts costs.... a current generation Class D amp, typically would require replacement of the amp board and all components, rather than repair... the Quad 606 gets a new lease of life after 30+ years with minimal cost, and is ready for another 30 years... the lifetime construction and disposal costs are amortised over many decades...

I am unconvinced that current class D amps such as ICE, Hypex, Purifi etc... can say the same...

Does it ever occur to some here that the 1980s Quad amps are about as appealing to many buyers as the old ugly dining room set your Mom tried to pawn off on you in early adulthood?

 

[IPunchCholla]

I'd think minimal would suggest replacing of aging electrolytics and cleaning of potentiometers and switches with adjustments of bias and offset. -A regular.

Well, I wouldn’t release my desoldering/soldering skills on anything I cared about. Bias adjustment and offset (assuming a screwdriver potentiometer deal) would be doable for me. So do you have a sense of what it would cost to pay someone to do the desoldering/soldering bit?

 

[tmtomh]

Well, I wouldn’t release my desoldering/soldering skills on anything I cared about. Bias adjustment and offset (assuming a screwdriver potentiometer deal) so do you have a sense of what it would cost to pay someone to do it?

"But it's really not that hard"

"But if you really care about environmental sustainability you would just learn how to do it yourself"

What are the actual failure rates for 1960s, 1970s, 1980s, and 1990s Class AB amps and receivers? What percentage of such units get DIY repairs versus getting disposed of, versus getting packed up, loaded onto shipping trucks, transported to repair centers, worked on, and then transported back?

Without this kind of information - and without, apparently, any desire to discuss these factors - it just seems like we're all just emphasizing the factors that seem to support the view we came into this thread holding. You know, like the OP did.

 

[ahofer]

it just seems like we're all just emphasizing the factors that seem to support the view we came into this thread holding

You've been on the internet before, right?

 

[tmtomh]

You've been on the internet before, right?

Yes, and I've been on ASR before too. We're supposed to be better than that - not to mention, IMHO it's even more insidious when folks selectively bring up their favorite factors in the very same comments where they're chiding others for not taking all the factors into account.

I don't know what the sum total of the various variables says about Class AB vs Class D when it comes to "efficiency." And neither does anyone else, including John.

And I don't know how we'd even compute the sum total, since there are so many variables and we lack sufficient empirical data on a lot of them to properly weight them, and so on.

And I don't know how we could ever even come to any sensible estimate or hypothesis, given that "efficiency" is so ill-defined in this thread, thanks to @restorer-john 's silly OP and his opportunistic shifting of the definition whenever he feels like it.

Amp boards/modules aren't power supplies. We get it.

Idle and/or low-output power consumption is inefficient for all amp topologies. We get it.

The cheap, "chip amp" Class D amps are in small cases and not always sufficiently cooled. We get it.

And I would add, the cheap Class D amps are sometimes paired with external PSUs that prevent them from reaching their rated power specs. We get that too.

Everything else in the 300+ comments so far seems to be waste heat.

 

[Deleted member 48726]

Well, I wouldn’t release my desoldering/soldering skills on anything I cared about. Bias adjustment and offset (assuming a screwdriver potentiometer deal) so do you have a sense of what it would cost to pay someone to do it?

Money. But it should be seen over 20-30 years and maybe it isn't even needed anyway. This in contrast to throw away and buy new. Which ever is the best is seemingly subjective until concrete LCA but I'd rather repair and keep.