EPRD isn't a term that's used in engineering circles, even if it's a more valid descriptor than than the invented term "RMS power".
Any amplifier that relies heavily on NFB to present a low output impedance can be brought undone by a nasty capacitive load, and that includes Bruno's hypex modules, particularly when knowing that the output filter is also within the feedback loop.
When time permits I'll hook up the sig gen and scope and run some tests to see how well the NC500's perform on a typical square wave test Vs a class AB design.
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Thanks George, my bad - typo.
Typically, in "eng" speak impedance is expressed as a value with a phase angle (polar form) or real + reactive (rectangular form).
EPDR is obviously a means of expressing power dissipated in the amplifier based on instantaneous values of voltage and current at a specified frequency. In other words, a reverse engineered value.
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Bingo arty_vandelay. However, it is specific to linear amplifiers where that instantaneous voltage represents a large voltage drop across an output device operating in the linear region at a given current and hence high instantaneous power. As the output devices in Class-D are not operated in the linear region, it has little meaning. What EPDR hits really hard is BJT output stages as BJT devices have secondary breakdown mechanisms impacted by instantaneous power (or accurately power and voltage), even if they can handle the current delivery. arty_vandelay23 posts11-24-2019 8:43pmEPDR is obviously a means of expressing power dissipated in the amplifier based on instantaneous values of voltage and current at a specified frequency. In other words, a reverse engineered value. |
arty_vandelay
Yes, if the Wilson Alexia didn’t have a negative phase shift of -45’ degree in the bass causing an EPDR of 0.9ohm, then it would be an easier load for the amp to drive, but still it would be 1.8ohm and still needing an amp with good current delivery. Definatly not OTL or P/P tube or even most complimentary n & p channel Mosfets, unless they are push pull N channel only, then those can get some current going, like the Solution amps (or similar) I believe. Cheers George |
georgehifi,
EPDR does not define "difficulty" to drive the load per-se, even though it was defined that way in consumer audio media. It is illustrative of the thermal stress that is put on the amplifier output devices instantaneously. The peak current at the worst case EPDR is not the peak current of the amplifier.
Good current delivery with complimentary P-Channel is certainly possible, but better performance these days can be done with N-channel so that is normally the preferred architecture.
Note that MOSFETs don't have secondary break-down effects, hence EPDR is not nearly as critical for FET output stages. They don't mind high instantaneous power.
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It's probably worth making the point that a person who owns a pair of Alexia's is probably driving them with a decent amplifier. Most, if not all high-end class A-AB designs are usually very over-engineered to avoid device failures and to be able to drive the sorts of difficult loads that will inevitably be presented with ease. Also, when the difficult load is isolated to a relatively narrow bandwidth as is typically the case it's really not a significant issue.
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Like the Halcro Eclipse with its incredible specs; 110kg/250 pounds, 135,000$ 😉 |
atdavid516 posts11-25-2019 11:00amNote that MOSFETs don't have secondary break-down effects, hence EPDR is not nearly as critical for FET output stages. They don't mind high instantaneous power.
When did you last look at a MOSFET SoA plot? Its true that going back 30 years or more they generally didn't have secondary breakdown issues but these days its rare to find an SoA plot which is purely thermally limited. |
Slumming it
abraxalito?, did you got bored over at the other place?
Cheers George |
Like the Halcro Eclipse with its incredible specs ; 110kg/250 pounds, 135,000$ We had a friend that knew Bruce Candy and had the DM88 monoblocks, he used them with Wilson 6, 7 and 8’s, they were "nice and transparent" and could go loud, but a bit ho-hum, kinda boring, no life to the music, nothing that grabbed your attention and or emotions. Cheers George |
@georgehifi not much going on over there recently is there? |
No it’s quite, but at least there not too much voodoo there like here, lots of snake oil peddlers here, a bit of undercover shilling going on for small manufacturers, their threads can eventually get removed or closed.
Cheers George |
Admittedly most MOSFETs designed today are designed for pulse operation and the long pulse/DC rating of those MOSFETs is less than the rated current. That is a thermal derating though due to rapid heating of the usually quite small die. You can see that on the data sheet if it has a thermal response graph. MOSFETs designed for operation in the linear region (market that seems to be getting smaller) have larger die. This is different from the secondary breakdown of BJTs cause by current concentrating in a small area causing thermal runaway. When did you last look at a MOSFET SoA plot? Its true that going
back 30 years or more they generally didn't have secondary breakdown
issues but these days its rare to find an SoA plot which is purely
thermally limited. |
Like the Halcro Eclipse with its incredible specs; 110kg/250 pounds, 135,000
In line with laws of diminishing returns, but it is the best if you think least distortion = best. Distortion @ 100W into 4 ohms is on par with small signal performance of the best op-amps. If / when Halcro goes class D for their flagship amplifier, only then can it be said that class D is as good or better than AB. |
arty_vandelay
If / when Halcro goes class D for their flagship amplifier, only then can it be said that class D is as good or better than AB. You can put these into the same list. (Except for Rowland they sold out to the Class-D$$$$.)
Bob Carver
"I built many of them right here in my own laboratory with the thought they could and would fulfill that final promise.... I was never able to build a Class D amplifier that sounded as good as a linear one."
John Curl (Parasound, CTC, Vendetta Research, Constellation)
"Some version of hybrid Class A/D looks like the future in optimum audio design."
Cyrill Hammer (Souloution)
"if you want to have your product performing at the cutting edge it is not possible with today’s known switching technologies. In order to come close to the performance of the best linear design we would need high-current semiconductors that provide switching frequencies of several MHz or even GHz."
Lew Johnson (Conrad Johnson)
"I tend to think that Class D circuit design is an approach best relegated to producing low-cost, physically manageable multichannel amplifiers—where one might accept some compromise in sound quality for the sake of squeezing five, six, or seven 100 watt channels into one moderate-sized package for a budget home-theater installation."
Vladimir Shushurin (Lamm)
"No, it is not. And I would like to respond to the second part of this question with an allegory. Any field of human activity defines a number of requirements which, when properly implemented, guarantee a positive outcome.
For example, the basic requirement in the army and sports is an able-bodied individual. So, it would be quite natural to concentrate on searching for such an individual (especially as we know where to find him).
However, out of the blue we decide to choose a feeble-bodied person who, on top of that, is encumbered by various diseases. Having made this decision (which is a priori improper) we start justifying it to ourselves and others by citing the great state of our medicine, which is capable of curing many ailments."
Fumio Ohashi (BAlabo)
"No. Class D can’t really be considered for super-high-end performance in its present stage of development, although it can be fine for mid-market products."
Nelson Pass (Threshold, Passlabs)
"Does a $10 bottle of wine compete with a $100 bottle? Of course it does, and it often wins based on price. Right at the moment Class D designers seem to be still focusing on the objectively measured performance of their amplifiers. I expect that at some point the economics of the marketplace will encourage them to pay more attention to the subjective qualities, and then they will probably play a greater role in the high end."
Jürgen Reiss (MBL)
"I have worked a lot lately with Class D. Ninety-nine percent of Class D circuits are not competitive with linear circuits.
Most Class D sounds sterile. It’s tricky to figure out what to do to compensate for that."
Jeff Rowland
"I consider Class D to be highly competitive in the present, and to offer an evolutionary pathway of audio design that may produce even more astonishing results in the future."
Thorsten Loesch
I have yet to hear a pure class D Amp I’d rate above "below average for solid state" (which is not very high performance).
In a little update of my classic "Valve Analogue Stages for DAC’s #" I wrote:
"Perhaps more crucially, so called Class D Amplifiers, which have in recent times sprouted up like mushrooms after a warm rain, continue to use the straight two or three level modulation scheme described above. And thus they still require the use of heavy handed noise shaping to attain anything like acceptable 16 Bit Audio performance.
The clock frequencies for these amplifiers are usually at 300 KHz to 1MHz in the best cases. That is 3,000 to 10,000 times lower than what is required to attain 16 Bit / 44.1 KHz performance without noise shaping and
other forms of signal manipulation!
And again, one is baffled and perplexed by the rave reviews many Class D amplifiers receive, as baffled as one was about the late 90’s reviews of timeslicing dac’s. The best of breed I have auditioned were certainly not bad; however in direct comparison to the best available valve and solid state amplifiers they do not produce a very good sound. Well, at least they offer novelty and the reviewers something to write about other than another (however good sounding) 8 Watt valve amp.
Incidentally, the best sounding Class D amps tend to be really low power single chip devices (putting out little more than the 8 watt valve amps), presumably because they are faster AND because they always work near what one might call “full scaleâ€, if they would be dac’s. On second thought, they of COURSE are DA Converters and where a Class D amplifier accepts analogue input directly it is an A2D converter followed by a power D2A converter!
What an insight!?"
Mark Levinsons interleaving of multiple Class D Amplifiers is potentially a step in the right direction, but does not go far enough.
Personally I think that the best option would be something that combines a Class D Amplifier for the heavy lifting with something Class A for fine detail. Probably implemented in the style I did for AMR’s AM-77 "Jikoda$" Style. In this case both of the circuits involved can operate fully open loop.
In many ways the problems in Class D Amplifiers are analogous (but not identical to) those in Class B Amplifiers (but without an option to implement Class AB or Class A) so similar solutions apply.
Thorsten Loesch
All Class D amplifiers are essentially delta-sigma DAC’s.
If the input is not digital PWM signals (aka "DSD") but analogue audio then it is also a Delta Sigma Analogue to digital converter...
Now DSD (aka SACD) which to my ears fails to come close, never mind equal true PCM CD Replay in most aspects of sound quality, operates at 2.8MHz switching, or around 10 times as fast as common Class D Amplifiers...
Why anyone would want to listen through an A2D followed by an D2A Converter that are around 10 times worse than single speed DSD is beyond me.
But with enough hype and snazzy naming it cannot help but sell high and wide.
And Thorsten Losch is one of Bruno Putzty's (hypex) best mates, bit of a slap in the face. Cheers George |
I am not sure what the goal is with these quotes. Pretty much none of these people are experts in signal processing, and to long term advance the start of the art of class-D, it will require a different knowledge set than linear amplifiers. Thorsten Loesch particularly shows his lack of knowledge. I have no idea why he even made a comment.
"Perhaps more crucially, so called Class D Amplifiers, which have in
recent times sprouted up like mushrooms after a warm rain, continue to
use the straight two or three level modulation scheme described above.
And thus they still require the use of heavy handed noise shaping to
attain anything like acceptable 16 Bit Audio performance.The clock
frequencies for these amplifiers are usually at 300 KHz to 1MHz in the
best cases. That is 3,000 to 10,000 times lower than what is required to
attain 16 Bit / 44.1 KHz performance without noise shaping and other forms of signal manipulation!?"
How do you take someone seriously who has such flawed views of what is possible or the underlying technology? Fortunately, we can count of people such as Nelson Pass, and Jeff Rowland, even John Curl to offer a more balanced (and probably more informed) view of where Class-D is and can go. |
I once made the class D > DSD analogy on another forum and was met with enormous hostility from the Class D faithful.
The believers provide the missing bias.
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Anyone that thinks GaN is all the same, send me Wallys $2K attempt at lowballing the market and "stealing " all the sales as the lemmings think anything GaN is the same.. Il compare it to the best Ive heard AGD, and if Wallys is undetectable I'll be honest and admit it , then give the news to AGD and tell them to get thier ass to work along with sending it back with $100 and a thank you for letting me compare. I am guessing the AGD will embarass the crap out of Wally and his huge claims of greatness just due to using a certain material. It will help to prove the point that curcuit design anmd layout trumps everything. Maybe Ill put a Silicon based Class D against .... maybe I'll put an Ice power silicon Class D made by one of my favorite circuit designers against Wallys GaN amp... my purpose is to show that design is far more important than material. I simply dont think Wally has any Genius designers making his $2K amp.. Lets prove it shall we ? |
GaN FETs suitable for a Class-D output stage and superior to silicon devices are relatively inexpensive now. Even in a $2,500 unit, they use of GaN shouldn't command that much of a premium.
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Thorsten Loesch particularly shows his lack of knowledge.
Agreed - its obvious he conflates 'clock rate' with 'symbol rate'. Its not the clock rate of the classD amp which is around 500kHz, rather the symbol rate. There's no clock rate in fact - because classD is an analog amplifier, not a digital one. Since there's no quantization of the symbol widths his comparison to DSD or S-D DACs is totally meaningless. |
A Class D amplifier is a "analog amplifier" with a two state (binary) output stage modulated by the output of a comparator that compares an analog signal with a reference waveform.
Ultimately I guess it boils down to the definition of "analog", but there is quite a big difference from a linear amplifier that simply "amplifies" a signal, and class D which recreates or reconstructs the signal.
In the strict sense, class D isn't an amplifier it's a "reconstructor". |
Is it not demonstrated that a true flying machine, self-raising, self-sustaining, self-propelling, is physically impossible?
— Joseph LeConte, November 1888 It is apparent to me that the possibilities of the aeroplane, which two or three years ago were thought to hold the solution to the [flying machine] problem, have been exhausted, and that we must turn elsewhere.
— Thomas Edison, November 1895
I can state flatly that heavier than air flying machines are impossible.
— Lord Kelvin, 1895 I have not the smallest molecule of faith in aerial navigation other than ballooning, or of the expectation of good results from any of the trials we heard of. So you will understand that I would not care to be a member of the Aeronautical Society.
— Lord Kelvin, 1896
The present generation will not [fly in the next century], and no practical engineer would devote himself to the problem now.
— Worby Beaumont, January 1900
There is no basis for the ardent hopes and positive statements made as to the safe and successful use of the dirigible balloon or flying machine, or both, for commercial transportation or as weapons of war.
— George Melville, December 1901 The demonstration that no possible combination of known substances, known forms of machinery and known forms of force, can be united in a practical machine by which men shall fly along distances through the air, seems to the writer as complete as it is possible for the demonstration to be.
— Simon Newcomb, 1900 Flight by machines heavier than air is unpractical and insignificant, if not utterly impossible.
— Simon Newcomb, 1902 It is complete nonsense to believe flying machines will ever work.
— Stanley Mosley, 1905
The aeroplane will never fly.
— Lord Haldane, 1907
1920 “No flying machine will ever fly from New York to Paris.” — Orville Wright, inventor of the airplane.
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Since there's no quantization of the symbol widths his comparison to DSD or S-D DACs is totally meaningless.
Wonder if his mate Bruno Putzy (Hypex) put one on his chin after that, I think they're still mates. |
Are they really great mates? If so then Thorsten would do well to bury himself in Bruno's technical papers in relation to classD and ask his buddy pertinent questions when he gets stuck. |
I think I just saw a pig fly over my house.
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I think I just saw a pig fly over my house. Thorsten’s chin going into orbit |
https://agdproduction.com/gantube.html If I’m reading this correctly, the best way to make GaN-based amplification to sound more tube-like is to build the components into a tube??? BTW, again no rating into 2 ohms.
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Given the target market, you can't fault someone for making it look like a tube amplifier. Can't comment on the 2 ohms, or the sound, but fairly sure that clear acrylic cover would not cut it as a required fire barrier required for AC products in North America.
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I think George was referring to me when he said a member here who changes the Mosfets for Bi-polar transistors. I agree with George on what he is hearing in sound differences between the designs. This came about as I repair Counterpoint power amps which used mosfets and then Mike Elliott redesigned the amps because he could not find the Mosfet replacements and then changed the design switching to bi-polar transistors. For the Counterpoint amps you can almost swap out the mosfets and install bi-polar transistors with a few changes and bias adjustments. Since we repair so many of the amps, I can compare the sound to one another. We now build our own amps after the new design that we implemented when we completely rebuild the Counterpoint power amps point-to-point wired basically using the chassis and the transformer so they are no longer Counterpoint amplifiers. You really do have to have a trained ear to hear the differences especially when you compare them side-by-side. Happy Listening. |
Thorsten Loesch
All Class D amplifiers are essentially delta-sigma DAC’s. This statement is false. |
Mike, I have RicSchultz's EVS 1200 (class D) which sounds WAY better than any of my previous Ds, including EP 100.2SE monos, Audio Alchemy DPA-1, and PS Audio M700s
I am awaiting a Voyager GaN amp to compare. PM me your email since YT suspended my account I can no longer post to your videos
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Hey @tweek1 Glad to hear you are going to be an early adopter. I’m thinking of trying one of these as well. I do wish they would have released a mono block version but I’m sure they will if the stereo version sells well. I don’t see that they are bridgeable to mono. Do you know? Anyway I am currently running a pair of EP 100.2se’s as mono blocks driving EP 2.7’s. I think they sound great together. They were designed to work together so that is not surprising. Are you still running Emerald physics speakers? I forget which model you have/had was it the KC11?
I don’t get comparing a $2500. amp to 15,000 - $30,000. amps. Of course they will not likely be quite as good. Wally is about value products not chasing the uber high end. Just look at the case’s of the amps. These are designed to be affordable and if they are decent performers I’m sure they will out sell the high dollar ones. The designer of the Living Sound Audio (LSA) amps is the same one who designed the Emerald Physics amps and helped design the EP range of open baffle speakers. In fact he is currently helping me get the best out of my EP2.7’s that I bought from him. I have talked to him a few times lately. I plan on asking him some more about these amps.
tweek1 I look forward to your thoughts after you get it. Do you have an ETA?
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+1 pirad
GFi, your designer quotes lack dates. Also, most of them have a company to protect, so there comments can mostly be taken with a small grain of salt. Still, you hang in there with your negativism
BTW, while I find all the technical comments worthy of discussion/debate you have hijacked this GaN thread. Take it to a new thread
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Sonicjoy
In fairness, the EP amps design is ~ 5 years old, which is ancient compared to the newest IcePower modules in the EVS 1200, plus Ric employs lots of tweaks that commercial designs would not
Also, post EP amps; my Audio Alchemy DPA-1 and PS Audio M700s benefited from upgraded interconnects and speaker cables (to 100% WW, series 7s and 8s), but I still think the EVS 1200 is by far a superior amp to all of them, at least with my EP KCIIs, which has an 8" mid-range and twin 10" woofers.
Your 2.7s have 12" mid-range and twin 15" woofers, meaning your sound is likely bigger, fuller and richer in tones, though the KCIIs are excellent in their lane, my room is too big for them by themselves, but I could not get the 2 SVS subs (12") to blend even with the EP BOM, so the KCIIs are flying solo. And still I am very impressed with the overall sound.
That said, EP 2.8s should arrive any day now. I was expecting to have the Voyager well in advance so I could make apples to apples comparisons with my KCIIs, but it is still not here, and I will have someone coming for just a few days who has intimate knowledge with setting the 2.8s up, which means any thoughts I have on the Voyager vs EVS 1200 comparison will be pretty useless, at least until I get used to the 2.8s then compare the 2 amps
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Very cool! I predict you will like the 2.8’s. They are the same basic speaker as the 2.7’s just with carbon fiber mid’s and woofers and an upgraded tweeter. My 2.7’s have the upgraded tweeters and have had the crossovers tweeked by GR Research for the new tweeters. If I can use one word to describe the sound it would be "Power!" Of course one word is not enough. Maybe effortless power and dynamics. And the bass is to die for. Just wonderful! Deep powerful and not boomy at all. And the impact of drums is so life like and did I mention vocals? Just "power". I too tried them with my Vandersteen 2wq pair of subs but they are so efficient that the subs can not quite keep up. I took the subs out and the bass actually increased. It really is better than sub woofer bass. (My room is medium sized with cathedral ceilings. Speakers 5 feet from the front wall.) I know you have a good idea of the overall sound and room loading of the open baffle design. Be sure and give them lots of time to break in before judging them. Couple hundred hours at least. Oh and mine have the single input crossover with no DSP.
I have not tried any other amps yet with them but am researching that now. And I am not afraid to try new tech. The EP’s are such a good value though. Picked them up for $600. each used.
Regarding the Voyagers I did find out from the designer that they use the same GaN transistors some of the other $30k GaN amps. He says they are really something special. I hope to find out soon. Looking forward to your comparisons. Please keep us posted.
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Underwood HiFi says they have shipped out a small batch, maybe 20, Voyager GaN amps, more powerful than the original design, Who got one and how does it sound? |
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@sonicjoy
$600 for 2.7s. Were they stolen LOL
My understanding is the concentric 12" is not carbon, just the 2 @ 15s/side
I have been enjoying the 3.4s with upgraded XOs for over a year, supplementing them with 2 old SVS powered subs 12" one is a plus, the other an ultra, but did 2 things recently that took them to much higher level of enjoyment. The 2.8s have been stuck in CDC warehouse for almost 2 years: too long a story, but would make a great novella. The short story is the trucker bringing them was also transporting chemicals to make a LOT of fentynol
Recently I replaced an optical cable with Pangea XL coax ($150) to huge grins, BUT, then I started playing with the subs XO point. Where I had them @ 80hz, I now have them at ~ 100hz which freed them up of going too high
hth
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