F
freemansteve
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Surely no need? The power density of a CPU must be a lot higher than power transistors?
Very few not running fans these days.
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Class D amp long term reliability
- Thread starter sophie smith
- Start date
Surely no need? The power density of a CPU must be a lot higher than power transistors?
Very few not running fans these days.
Vacceo
Major Contributor
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That´s why I asked for DIY-ers. It´s the kind of overkill project someone would do. Plus you can attach RGB to your amp too, everyone knows that gives a +20 SINAD.
As an aside, fewer parts does not always mean more reliable or easier to repair. Bob Pease was fond of debating that with the QA team; removing protection devices reduces parts count, but is the end result really more reliable?
Power density in small high-power ICs can be very high, leading to temperature spikes and such that impair performance and reliability. Most amps run along at fairly low average power, only getting above a few watts for peaks, but other components in the amps still dissipate power, and even for class D a 100 W peak still wastes maybe 10~20 W as heat.
Another factor is rework since many parts are surface-mount requiring special tools and skill to remove and replace. And a durn good magnifier, at least in my case. Add to that parts may lack identification marks (some manufacturers actually cover them to make it harder to clone their devices) and may not be available after a few years. This latter is IMO one of the biggest issues with repairing today's electronics in general; 5 to 10 years is the lifetime of many ICs, so in the future repairing a 30-year-old SMPS or amplifier module (or anything else) is likely not as simple as repairing a 30-yo class AB amplifier today. Not to say that some of us have not struggled trying to find replacement driver and output transistors for some of our dear old class A/AB amps...
FWIWFM - Don
Power density in small high-power ICs can be very high, leading to temperature spikes and such that impair performance and reliability. Most amps run along at fairly low average power, only getting above a few watts for peaks, but other components in the amps still dissipate power, and even for class D a 100 W peak still wastes maybe 10~20 W as heat.
Another factor is rework since many parts are surface-mount requiring special tools and skill to remove and replace. And a durn good magnifier, at least in my case.
Add to that parts may lack identification marks (some manufacturers actually cover them to make it harder to clone their devices) and may not be available after a few years. This latter is IMO one of the biggest issues with repairing today's electronics in general; 5 to 10 years is the lifetime of many ICs, so in the future repairing a 30-year-old SMPS or amplifier module (or anything else) is likely not as simple as repairing a 30-yo class AB amplifier today. Not to say that some of us have not struggled trying to find replacement driver and output transistors for some of our dear old class A/AB amps...FWIWFM - Don
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Lots of praise for the Yamaha NS 1000. Is it worth buying a used pair today around 1200 USD? Would there be any benefit to bi-passing the crossover an tri-amping each individual driver?
Those kind of experiences with class d seem to be quite common among people that I know personally. I have been involved in this scene since I was a young teen in 1972 (friends where in local rock bands & I started running sound for them). Yes, I know people who blew up good class A/B amplifiers (me included). But (as far as I know, it was always a learning experience of "what not to do" [both me and the others that I knew then].
It seems like with todays class D amplifiers there is a lot of "it just stopped working for no apparent reason". Now, don't get me wrong, I think that there are a lot manufacturers & assemblers that take the time to get it right (particularly in our segment of what we look for in equipment). But it is still something that one must do some research on (and even then it could be an 'iffy' situation for longer term reliability. Many of the former "name brand standard" bearers have not brought the expertise needed to the table. And many of the ones that seem to be doing class D right seem to "here today & gone in 3 or 4 years". That loses the "tribal knowledge of those that do do it right and us (the consumer) is left to finding another company that is doing it right.
Of course, part of it is our (the consumer) own fault for expecting tiny form factors (not enough heat dissipation long term), AND inexpensive (which means (not much research on reliability because research costs money AND CHEAPENING the components used to just barely enough to get make it through the warranty period. That causes those that do it the right way to have to cut corners too, because they can't compete on price. Until us consumers get out of the mindset that we must get something for the cheapest price possible, there will be this issue in all fields (EXAMPLES: refrigerators, washing machines, air conditioners, microwaves, TV's, cars, many things don't last the 10, 15, 20 years that it used to because of competing on price alone). And then some manage to compete on prestige & make great money for a good but not great product.
It's almost like a lottery, a few win the reliability prize but most don't. Be careful & perhaps don't be an early adopter.
MY 5 class A/B NAD 2200s are good enough for me at this point. Longevity proven &:
It is power measurements where the magic of this amplifier comes to life so let's look at that with 4 ohm load first:
We can see a kink in distortion when we hit 200 watts as the unit sails past that to produce whopping 337 watts per channel, both driven! Per design characteristics, you can have much more during momentary peaks:
Wow, we have one kilowatt of power coming out of this amp in short duration!
Lab Input Measurements
I was surprised that the frequency response was not flat but was relieved to see later in the thread that this is due to insertion of low and high pass filters. So here is the frequency response with Lab input that doesn't have such a filter:
Response now (in green) as it should be, ruler flat to below 10 Hz, and well extending past the 40 kHz limit of this measurement.
Zoomed:
And signal to noise ratio:
Conclusions
Nice to see innovation like this from equipment that is over 30 years old! Shame on manufacturers that produce amplifiers for much less power, more distortion and higher prices these days. No, you don't get a fancy case here and sheet metal is strictly budget category. But you are not going to sit on the amp. The guts are where it matters and NAD 2200 delivers.
NOTE: the output relay on stock 2200 gets corroded and fails over time. There are videos and DIY threads on how to upgrade the relay there to fix the problem. The unit tested here has that fix. Other than that, there are not reports of many other reliability issues even though NAD products are often said to be less reliable than other brands.
Overall, I am happy to recommend the NAD 2200. I almost gave it the highest honors but given the upgraded nature of the test unit, and the fact that used amps may have issues, I avoided that. But you could have easily pushed me to give it the golfing panther.
I had a similar experience 3 years ago. I bought 2 Class D mono blocks; not a major brand, but well reviewed in the audio press; One stopped working for no apparent reason. Repairs are out of the question, too expensive. Result: I would not buy a class D amp with your money.Those kind of experiences with class d seem to be quite common among people that I know personally. I have been involved in this scene since I was a young teen in 1972 (friends where in local rock bands & I started running sound for them). Yes, I know people who blew up good class A/B amplifiers (me included). But (as far as I know, it was always a learning experience of "what not to do" [both me and the others that I knew then].
It seems like with todays class D amplifiers there is a lot of "it just stopped working for no apparent reason". Now, don't get me wrong, I think that there are a lot manufacturers & assemblers that take the time to get it right (particularly in our segment of what we look for in equipment). But it is still something that one must do some research on (and even then it could be an 'iffy' situation for longer term reliability. Many of the former "name brand standard" bearers have not brought the expertise needed to the table. And many of the ones that seem to be doing class D right seem to "here today & gone in 3 or 4 years". That loses the "tribal knowledge of those that do do it right and us (the consumer) is left to finding another company that is doing it right.
Of course, part of it is our (the consumer) own fault for expecting tiny form factors (not enough heat dissipation long term), AND inexpensive (which means (not much research on reliability because research costs money AND CHEAPENING the components used to just barely enough to get make it through the warranty period. That causes those that do it the right way to have to cut corners too, because they can't compete on price. Until us consumers get out of the mindset that we must get something for the cheapest price possible, there will be this issue in all fields (EXAMPLES: refrigerators, washing machines, air conditioners, microwaves, TV's, cars, many things don't last the 10, 15, 20 years that it used to because of competing on price alone). And then some manage to compete on prestige & make great money for a good but not great product.
It's almost like a lottery, a few win the reliability prize but most don't. Be careful & perhaps don't be an early adopter.
MY 5 class A/B NAD 2200s are good enough for me at this point. Longevity proven &:
It is power measurements where the magic of this amplifier comes to life so let's look at that with 4 ohm load first:
We can see a kink in distortion when we hit 200 watts as the unit sails past that to produce whopping 337 watts per channel, both driven! Per design characteristics, you can have much more during momentary peaks:
Wow, we have one kilowatt of power coming out of this amp in short duration!
Lab Input Measurements
I was surprised that the frequency response was not flat but was relieved to see later in the thread that this is due to insertion of low and high pass filters. So here is the frequency response with Lab input that doesn't have such a filter:
Response now (in green) as it should be, ruler flat to below 10 Hz, and well extending past the 40 kHz limit of this measurement.
Zoomed:
And signal to noise ratio:
Conclusions
Nice to see innovation like this from equipment that is over 30 years old! Shame on manufacturers that produce amplifiers for much less power, more distortion and higher prices these days. No, you don't get a fancy case here and sheet metal is strictly budget category. But you are not going to sit on the amp. The guts are where it matters and NAD 2200 delivers.
NOTE: the output relay on stock 2200 gets corroded and fails over time. There are videos and DIY threads on how to upgrade the relay there to fix the problem. The unit tested here has that fix. Other than that, there are not reports of many other reliability issues even though NAD products are often said to be less reliable than other brands.
Overall, I am happy to recommend the NAD 2200. I almost gave it the highest honors but given the upgraded nature of the test unit, and the fact that used amps may have issues, I avoided that. But you could have easily pushed me to give it the golfing panther.
Hello,
Would say that IMHO there is better equipment is all classes/design types. Some is built with components over specified for max rating quite a lot and some push the boundaries of the specs to save money. Some has much better cooling as well. Saying any one type of design is good or bad is just saying nothing meaningful. Buy quality and likely you will be happy for a long time regardless of the type.
Well; the much maligned Carver amps are still doing great 30 years later; that IS saying something.
F
freemansteve
Guest
Bear in mind, we only ever rent stuff, when all is said and done...
And when good tech changes come, you can be agile, as the benefits come less painfully if you are not over-invested in the past.
Now, where did I stow that top-of-the-range Betamax?
And when good tech changes come, you can be agile, as the benefits come less painfully if you are not over-invested in the past.
Now, where did I stow that top-of-the-range Betamax?
antennaguru
Senior Member
1. I have had to replace Internet Radios that worked great for a few years and then the Internet Radio Station Aggregation Server "Reciva", owned/operated by the mega-company Qualcomm, was "discontinued" leaving a dearth of Internet Radios dead. The radio hardware was perfectly good but they can no longer connect to the 10K+ stations on the server, as the server is now gone. Tons of great radios became bricks.
2. I have had to replace several perfectly good Carbon Monoxide Detectors because they operated a clock inside them to make them inoperative at a pre-set number of hours of operation "for my safety". I know for a fact they would detect CO just fine for twice that time period, but had to buy new ones and was without any protection while waiting to obtain the replacements. The internal clock literally starts ticking when you first put a battery in it, and then when it gets to the programmed number of hours it fails with an error code that says to replace it. I have had other CO detector models made by the same manufacturer before the addition of the hour counter planned obsolescence feature was incorporated, and they still work fine at twice the life of the dead ones that timed out - and as validated by my CO sample spray test (the only real test).
3. The expensive telescope maker Celestion had a wonderful product called the "Sky Scout" and every one of them failed at a pre-determined date based on a calendar date on the GPS unit. It was a very cool unit that looked like a spotting scope you could sight at any celestial object, and with its internal GPS, inclinometer, and magnetic flux compass, it would tell you what celestial object you are looking at. It was a very expensive product and then POOF it was suddenly dead. There is no way to input coordinates, so they are all bricks.
4. Many years of Honda CRV Nav/Info-tainment Systems had their clocks go dead the beginning of this year due to some programming issue with the GPS epoch calendar. Now every time you start the car the big display on the dash says January 1st at 4:00 PM. The clock keeps time until you turn it off, and then it starts over at January 1st at 4:00 PM. Ground-Hog Day...
Hardware that includes Software clearly has the ability to stop working whenever the programmer wants, or because the programmer didn't know how to make the calendar work beyond some future date and the company's QC was deficient in protecting the customer of an expensive device from $hitty programming.
Vacceo
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I cannot distinguish any radiator or cold plate.
LOL >> Like they say "The whole kitchen sink!"
I wouldn't say that it is necessarily a conspiracy, I would say that some do by omission or ineptness (perhaps not doing real R & D or good R & D) & others look at a bigger picture (more sales by word of mouth from building a great, reliable product). From what I know of your products (from friends that live in Germany, Austria & Italy), you and your products work very well for as long as anyone I know has had them. And I particularly like the auto on circuit that some of your amps have. If I had the need today, there would be one class A/B amp in consideration, your class D and one other class D in the consideration pool. Barring accidents or disease...I may need another set of amps in the future. And no one in contention is one of the large, old school manufacturers (NAD is obviously not a consideration for me for a future amp purchase).
Sorry dumb question, why is there a plastic film between the thermal pad and the aluminum base plate? Isn't the MOSFET already isolated from the aluminum base by the thermal pad?
MakeMineVinyl
Major Contributor
I've seen it mandated by UL for shock hazard reasons if a transistor which has a metal backing happens to short to the heatsink.
restorer-john
Grand Contributor
It's the primary side, mains voltages and there are plenty of through hole solder pigtails which in a PCB flexing situation could contact the alu plate. Part of the double insulation requirement most likely as the distances are only a few mm. The 'plastic film' actually has device sized cutouts to ensure 'better' thermal contact for the devices.
Thanks for your reply!
But why double inslulate one side only? Is it because the smps side is "high voltage" zone and the amplifier side is low voltage (below 60v I assume)?
I just built a nc252mp amp with the Ghent audio kit and I noticed that the transformer that sits right on top of the smps MOSFET (very close to the explosion site in your pictures) gets incredible hot ( > 190 f ) while playing at moderate volume.
I understand that some components are designed to work at certain temperature, but given the high density of this board (capacitors close to the FETs and transformers), wouldn't it help if the overall temperature can be kept at a lower level?
Do you have any suggestions on improving the heat dissipation and longevity of the mc2522mp board?
I did sanded off the anodization coating on the chassis and pasted the board to the metal. I'm also considering replacing the factory thermal pads with some high end pads or even AIN (aluminum nitride ceramic). But any suggestions are appreciated!
MakeMineVinyl
Major Contributor
Use a proper heatsink. The data sheet for the modules basically says as much.
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