Just an observation and a question. Are there 'high end' Class D amps out there that are just as good as Class A, A/B amps? I realize that's a sensitive question to some and I mean no disrespect---but whenever I see others' hifi systems on social media, all of the amps are A or A/B. There's always Pass, McIntosh, Moon, Luxman, Accuphase, etc. Where are the Class Ds? For folks out there that want more power for less efficient speakers and can't afford the uber expensive Class As, A/Bs, what is there to choose from that's close to those brands? Thanks
I generally think of the Odyssey units more as PA amplifiers than serious audiophile gear. Throw lots of brute force at a problem, but not a lot of finesse ending up with a "warm" but bloated sounding box. If that is the sound you like, then I am not surprised the Cherry was not to your liking. It is transparent, not "euphonic".
Bruno is a promoter, but unlike many in the audio industry, actually has the technical chops to put something together.
Switching frequency was important 10+ years ago before people figured out putting the filter inside the feedback loop.
The claim the output filter is "deadly" to euphonics, again is "old" knowledge, see last comment about the placement of the filter in new higher end class-D amplifiers, not to mention a bit better practical understanding of how to tune class-D filters, however, keep in mind the filter is to keep ultrasonics out of the speaker.
@audio2design Okay what class D amp today can beat my Stratos? I can’t have fatiguing sound. Does the little Cherry just lack juice? My speakers are ProAc D30R.
Edit: it's a Stereo Maraschino with an external power brick, less than the 48V listed on the website but I forget the exact value.
madavid0: "
I don't think you guys really appreciate how deadly to euphonics that traditional class D output filter is. I didn't start out hating class D I developed that position after being burned many times being told this or that class D module was the revolutionary savior of the topology. I remain interested in GaNFET because it seems like that is what will finally be able to pull class D into the realm of quality audio."
Hello madavid0.
I believe the most prominent characteristic of the newer, good quality class D amps is neutrality, with no euphonics or anything else added or subtracted. In my experience, this high degree of neutrality is very revealing of everything upstream, even interconnect and power cable quality levels and differences are more easily detected. I know that Bruno Putzeys, the inventor and designer of the Phillips ucd, Hypex Ncore and the most recently the Purifi class D modules, has stated that he has steadfastly maintained a goal of optimum neutrality in all his modules in order to appeal to the largest number of potential customers. Based on my experience, the designers of most other class D amp modules, such as TI, Anaview/Abletec and Pascal, have apparently maintained the same neutral presentation goal. As to your statement "
I don't think you guys really appreciate how deadly to euphonics that traditional class D output filter is.", I don't know where you read this, why you believe it or what class D amps you've listened to, but it's definitely not true with my class D monoblocks. These are good quality units and, as I stated above, their primary characteristic is a completely honest neutrality, like the traditional audio ideal of a 'straight wire with gain'. It is definitely true that this level of neutrality very distinctly and articulately portrays the quality level of both the recording and the music but there's absolutely no elimination or theft of 2nd or 3rd harmonics and euphonics taking place. If the music contains these euphonic qualities, and the recording is of sufficient quality to have captured them, then they are faithfully amplified and reproduced. I happen to appreciate and prefer utilizing very neutral and revealing amps in my system while understanding that numerous others seem to prefer a bit of flavoring. However, I believe this is a topic best left for a separate thread.
Ralph, if GFi is right, that you are close to releasing your class D, I volunteer to compare/comment on it vs my much beloved EVS 1200, dual mono IcePower AS 1200 modules with lots of Rics pixie dust. My speakers are EP 3.4s 12' concentric driver with polyester tweeter. Digital is a Oppo 105 with upgraded LPM, Furutech rhodium IEC with silver tail to LPM and ground, plus jumper to replace 110/220 switch. Series 8 WireWorld ICs and Series 7 speaker cables. CorePower 1800 into 20 amp dedicated line
George is correct. Lack of switching bandwidth is the problem. I know
Bruno Putzeys claimed differently in an old interview, but he's mostly a
self-promotor so no one should take what he says as gospel truth.
For the record, Bruno Putzeys is the one that made self-oscillating class D amplifiers a reality, a practical thing. That's a pretty big deal; if you work out the math for that you are doing quite well. You better be good at calculus with multiple variables! He also is able to show the measurements to back up what he says about how the technology works. Attacking Bruno is really done at your own peril!
By 'switching bandwidth' I think you must mean 'switching frequency' since 'switching bandwidth' isn't a thing. And in this regard your statement is false. Based on the rest of your comments I would venture that you simply haven't heard everything that's out there, and just like traditional solid state amps and tube amps, there is a tremendous variance in class D implementation!
You might think of it this way: digital has come a long ways since 1981 when it first started showing up. Its common now to see scan frequencies of 192KHz; class D amps are commonly switching well over double of that. At the current state of affairs, the practical upper limit is around 600-700KHz before you really start to get into troubles with radiation and oscillation issues- the fact that Technics seems to have gone well past that says a lot about their engineering expertise. But Technics has to switch faster, since (if their claims are correct) their circuit is zero feedback, so they have to raise their filter frequency quite a lot in order to avoid phase shift at audio frequencies. Also for the record, self oscillating class D amps don't have to do this- their filter frequency can be lower since they can run so much feedback that it is able to correct for phase shift. @tweak1 Thanks for your offer!
@atmasphere, and @tweak1, Tweak1 is also getting Walter's Voyager GaN amp as well as having Ric's modded 1200AS amps, Ralph he deserves to be in your Beta testing.
Here are the class D I tried. Old ICEPower: Unlistenable junk. To be fair I didn't burn it in much (didn't know about burn-in back then). DriveCore 2: Very poor. Pascal (newer version forget the designation): Very tight control good imaging but also empty and not pleasing. MAYBE it needed more burn-in but I was running into the return widow. Cherry: Decent in some ways, couldn't compete with my linear amp. Actually I just moved it back into my main system to contrast and compare again now that I have new pre and source gear. Technics GaNFET: Dry, sterile, boring. Burned it in for over a month. The cheap integrated unit.
I haven't owned any Hypex amps. I've listened to some at shows but I do realize those are poor environments for critical listening. There was one nCore 1200-based unit I thought MAYBE warranted further listening but that was based on the "wow" factor of high-end class D's first impression.
How many class D do I have to listen to? Is there a The class D which disproves the "myth"? Did I just happen to miss the good ones?
The way to tell people who know and don't know what they are talking about is by the detail and depth of their posts. Ralph, jaytoy, and I talk about architectural specifics about Class-D, even where the filter is placed. We talk about device operating region. We talk in numbers specific to Class-D. One other person here who has a bugaboo and about Class-D and I think Ralph in general does not. I would argue that he cannot, and if he educated himself, he still would not be able as he would see his errors.
As Ralph has pointed out, there are many ways to skin the Class-D cat. High frequency open loop is just one method. Claiming it is the best is like claiming tubes of solid state is the best. We know many do it, but it is purely dogmatic. Implementation details can push either in a direction of like or dislike for a given person.
Tim also clearly laid out what I would agree w.r.t. modern high end class-D. It is targeted towards very neutral. Many don't like that. I am finding the Cherry very neutral. It does appear to have a better supply than what you are using. I have heard your present Odyssey a few times, one of my friends bought on reviews and did not keep it. I can see the allure, but it was not for him and and if you like that sound, the Cherry may not be your cup of tea, and I can't recommend one that will be, though they may be out there.
Technics GaNFET: Dry, sterile, boring. Burned it in for over a month. The cheap integrated unit.
I don’t claim to know all the Technics GaNFET units, but I am not aware of a "cheap" integrated unit and considering you are using relatively "cheap" Odyssey Stratos, I am not sure what you consider cheap. Even a new Cherry is a fair amount more money than a standard configuration Stratos. Do you mean the G700 which I don’t think uses GaN. SU-G30? .... that is $4,000.
I don’t have the engineering chops to add much to this discussion, and neither do I have a dog in this. It would seem to me that much of this difference of opinion might be about the theoretical possibilities vs.actual consumer available units that have actually been measured to offer those theoretical possibilities. My limited experience with Class D amps suggest quite a bit of difference between competing units, and though to this point none have convinced me to switch from standard ss amplification, I am truly excited by the potential of Class D (or whatever variation therein) amplification.
It was the SU-G30. I bought one used for $2500 if I recall. I meant cheap in relation to the other Technics GaNFETs. The Stratos was picked up as a "filler" amp until I get get something better like a Mark Levinson, Esoteric, etc., but they worked so well with the ProAcs that I haven't been in a terrible rush to move on.
I think I stated earlier in this thread that I used to own a pair of Nord Hypex NC500 monoblocks. There was a lot to like about them, and I think they delivered compelling performance for the price, but were not as engaging as I was looking for in the system I had at the time. But they convinced me that class D holds a lot of promise.
In the past year, I've had a lot of fun building DIY electronics (two pairs of monoblock amps and a preamp so far), so I've decided to try building a class D amp as my next project. I like monoblock amps for a number of reasons, so this project will be another pair of amps. I'm using the Purifi modules, and using a high-current linear power supply (1500VA) for each amp, and leaving room in the chassis to experiment with different input buffers.
This probably wouldn't be cost effective for a commercial product, but that's what's fun about DIY.
I'm going to use the Neurochrome buffer to start, but I've already started designing a buffer with a single-ended class A output that I'll try for round two. I've got a few other ideas in the works for other input buffers as well, so I can hear for myself how they affect the sound.
I hope to be playing music with the Neurochrome buffer by the end of the month.
jaytor I think I stated earlier in this thread that I used to own a pair of Nord Hypex NC500 monoblocks. In the past year, I’ve had a lot of fun building DIY electronics (two pairs of monoblock amps and a preamp so far), so I’ve decided to try building a class D amp as my next project. I like monoblock amps for a number of reasons, so this project will be another pair of amps. I’m using the Purifi modules, and using a high-current linear power supply (1500VA) for each amp
Interesting as this is what I have with a monoblock pair of NC500 modules.
Which impressed me and are in the Belcanto Ref 600M’s for class-D driven into a two way with Rahl ribbon, a very easy benign 6ohm load.
So these NC500 module (which btw are the ones in the Belcanto Ref 600M’s) are also in monoblocks but using big linear supplies and fed direct to their balanced input their input via the MSB R2R Discrete’s balanced variable 10ohm output so no need for any input buffer board. These sound even better than the BC Ref 600M’s. On those Rahl based two ways.
On the main system these NC500 mono’s have great bass/mid bass (very low bass is still bettered by my big ME bi-polar linear monoblocks with more weight substance to it) same as this amp but set 30w bias and no Class-A switchablity. https://ibb.co/QnYhmzL https://ibb.co/zb8vCgR Upper bass is the equal of the ME’s as is the lower mids (male voice). And then this is where the bigger difference starts, there seems to be a disconnect in the upper mids and highs from the bass with the NC500’s like they are two different amps doing bass and mid/highs. I’m putting it down to the switching frequencies output filters phase shift that reaches down to 1khz!!!! as can be seen in the phase shift plot in the graph of Class-D’s https://ibb.co/NC7sC8T which in this case is still -25 degrees at 1.5khz!!! and -75 at 10khz!!!!!!!
And this is why $$$$$ Technics with the GaN based, linear supply, SE-R1 I believe have the answer by increasing the switching frequency 3 x’s to 1.5mhz so then the filter can also be raised by the same amount and hence the phase shift goes up by 3 as well out of the audio band.
From an article on Audiophile Style - interview with Bruno Putzeys.
@Sagittarius: Class D has achieved very low levels of distortion, but is it possible for class D amplifiers to continue their evolution into something close to a straight wire with gain, i.e. minimal phase shift in the audio band? (A similar question from maty).
Bruno: The 1ET400 module has the frequency and phase response of a 2nd order Butterworth filter cornering at 60kHz. If you look at the phase shift of that, it’s very nearly “linear phase” in the audio band. To take some rough numbers, it if you have a circuit that has a 0.2 degree phase shift at 200Hz, 2 degrees at 2kHz and 20 degrees at 20kHz, that’s the same as saying it has “0.001 degree per Hertz” phase shift. That’s another way of saying that the whole signal is simply delayed by 2.8 microseconds. If you plot phase shift on a linear frequency scale that’s immediately obvious because you get a straight line. Of course a simple delay doesn’t change the sound. It’s literally the same as starting your music a few microseconds later.
Lars: My dad used to say that if you left a CD in its case without playing it back, it’d just sit there accumulating massive amounts of phase shift as time went by.
Bruno: What that matters to sound is how much phase shift differs from a pure delay. Anyone who’s ever done phase measurements on speakers will remember that you have to remove the time-of-flight delay from the data, for instance by marking the leading edge of the impulse response. Otherwise the linear phase shift corresponding to the distance between the speaker and the mic completely clouds the picture. In the case of the 1ET400 module it’s just under 1 degree at 20kHz. There never was a phase shift problem in class D, it’s simply a trick of the light that happens when you plot the phase response on a log scale without removing the fixed delay.
I believe Bruno in that modern class D amps with the output filter in the feedback loop do not have an issue with phase shift in the audio band. I actually thought the high frequencies on the Nord NC500 amps sounded very good (although being in my early 60s, high frequencies to me are not the same as they were 40 years ago).
My issue with the Nords on the system I had then was that they lacked body in the upper bass/lower midrange. I tried both the Sonic Imagery and Sparkos discrete op amps in the buffer stage. The Sparkos had a bit more warmth and was closer to the sound profile I was looking for, but gave up too much detail.
The Bel Canto Ref600M is pretty similar to the Nord in it's design approach, using a SMPS power supply and a custom input buffer. There aren't too many class D amps built with linear power supplies. The LKV Veros (mentioned earlier in this tread) is one of the few that does and has received good reviews, so I'm going to give it a try (partly because I'm comfortable building a linear power supply myself, and I don't want to just drop in a pre-built SMPS supply).
How many class D do I have to listen to? Is there a The class D which
disproves the "myth"? Did I just happen to miss the good ones?
Here are some tips. The first thing is avoid amps using switch mode power supplies. The reason for this isn't that SMPSs work, they do and they can be quite low noise. The problem with them is they are cheap to buy off the shelf and expensive to have built custom. Off the shelf units tend to have current limiting protection circuits that cause the amp to suffer a loss of bass impact. So unless you are looking at an enormous amplifier manufacturer, they won't be able to afford to have a supply built custom.
This means that the supply has to be a traditional supply: power transformer, rectifiers and filter caps. The power transformer current and the capacity in the supply can have a profound effect on the performance of the amplifier, since class D amps can go from almost no current draw to really quite a lot at full power. This really means that the supply has to be well filtered, and the power transformer high current, else the power supply will sag at higher power (bass notes).
If the amp is zero feedback look for a filter frequency of 100KHz or higher. This is to reduce phase shift at audio frequencies. If they won't publish details like that, consider looking elsewhere.
If the amp employs feedback, find out how much. If details like that are not published, consider looking elsewhere. The feedback **must** be in excess of 35dB! Any less and the artifacts of the feedback itself will become audible (as they are in traditional amplifiers).
I understand your skepticism! The first class D amps I heard I really thought were a joke. But they have improved over the years, so much that about 5 years ago I personally started to take them seriously, but even then some are terrible (we have a small 30 watt amp we use for testing, but it sounds really boring; I've not looked into it to see why that might be the case, but its pretty obvious to everyone in the shop) and some really work quite well and everything in between.
Problems with any amps shouldn’t be fixed by using even more feedback as a fix, it’s a added by the best designers to clean thing up a little and usually just local not global in an already well designed amp.
All the greatest amp designers say it. An amp should be reasonably good spec’d, and to use it just as a clean up tool. And the preference with the best is to use "local feedback" only by the best designers. Not global as being talked about here, and then even including the Class-D output filter in the global loop, what next throw the speaker wire and the speaker in the loop as well, like Trio/Kenwood tried all those years ago, utter sterilized disaster sound.
And using tube buffers with the capacitor coupling that’s needed. Is just colorized HF coverup softening job for the more serious Class-D sound problem.
@twoleftears - I am thinking about trying an input buffer using tubes.
I don't think I would consider using the Korg NuTube like ATM does. This is a pretty high-distortion device - specifically designed to add distortion for synthesizer special effects. It also has a bad reputation for microphonics, and is hard to swap in and out.
The 6DJ8/6922 tube that VTV uses is much better, but I'm not sure it's the ideal tube to use with the relatively low voltages I have available (approx +/-65v if I use the main supply for the Purifi module). I don't want to add another high voltage supply to drive a tube section, although I could consider a DC-DC converter as part of the buffer board design if I have to.
At any rate, I'd prefer to avoid the hassles of tubes, so I'm going to see what's possible with various solid state approaches first.
YOU are not one of the best designers. You are not even a designer. I would highly doubt you are an engineer.
Rules that apply to linear amps, do not apply to Class-D. As well, how well feedback works is a matter of amount of feedback, loop gain, and gain bandwidth.
The "best" designers are few and far between and they say things like this as generalities AND to sell THEIR amplifiers. They also only say them about non-class D amplifiers.
It is NOT used just locally either, it is used locally or globally, and both. Both work. Depends what sound you are trying to achieve and what your design parameters are.
Most discrete linear audio amplifiers are really quite simple. You think your music was recorded through low, local only feedback amplification chains after the microphone? Get real.
It is not 1973 or 1974 any more and no one is talking about Kenwood, but your ideas and knowledge seem to come from 1974.
And yes, throwing speakers in the loop is exactly where this is all going. Subwoofers with position and velocity feedback are already here and research is moving this up the frequency spectrum.
George see's one graph, or reads one article and he thinks that automatically applies to everything with the same basic name. That is technical ignorance talking.
georgehifi7,965 posts12-02-2020 5:53pm Problems with any amps shouldn’t be fixed by using even more feedback as a fix, it’s a added by the best designers to clean thing up a little and usually just local not global in an already well designed amp.
All the greatest amp designers say it. An amp should be reasonably good spec’d, and to use it just as a clean up tool. And the preference with the best is to use "local feedback" only by the best designers. Not global as being talked about here, and then even including the Class-D output filter in the global loop, what next throw the speaker wire and the speaker in the loop as well, like Trio/Kenwood tried all those years ago, utter sterilized disaster sound.
And using tube buffers with the capacitor coupling that’s needed. Is just colorized HF coverup softening job for the more serious Class-D sound problem.
You have no idea and do nothing but put **** on anything that's not "pro" Class-D. It still has problems sunshine, compared to the better linear amplifiers I and many other still say so.
You are nothing but a Class-D flag waver, that I believe probably has an commercial interest either now, soon or in the future with it.
At the price points, or close, the best of Class-D is every bit competitive to the best of the other classes. Calling me a Class-D flag waver is funny. I am doing nothing but pointing out your ignorance on a topic you are very passionate about, but know little about.
At the level of performance of good Class-D (which does not need to be very expensive), you really are just talking about preferred flavor.
You continued posting of old, and wrong information seems to know no bounds. When you have to use ignorance or perhaps lies to make an argument, that tells a lot. Why do you do it? The one who have proved repeatedly they have no idea is you. Quick search shows you have been on this wrong-headed EPDR crusade for what, 2+ years, and still you don't understand it. Ditto your class-D crusade with repeated postings of large phase-shift from an older technology Class-D amp. Ditto your insistence that Class-D must have phase-shift if the switching frequency is not MHz plus. Ditto your insistence that feedback must be bad (even though that is from a different architecture with different constraints). Ditto your insistence that doubling with reduction in ohms is essential to good sounds, without any consideration to what that means and why it normally does not matter, even with a low impedance load. Maybe you can't teach an old dog new tricks.
I will throw and old dog a bone ... namely I will throw you a bone George.
Explain, in detail please, exactly how EPDR impacts the ability of Class-D amplifiers to drive a load.
That is it, that is all you need to do. I am 100% certain you can't do it correctly, but here I am, have the floor, grab the bone, and show everyone you are the expert. Tell us exactly how EPDR impacts a Class-D amplifiers ability to drive a load.
I haven't heard much discussion on this thread thus far about the newer Bruno Putzeys designed Purifi Eigentakt class D modules that outperform his previously designed Hypex NCore NC-1200 modules, both in measured performance and subjective listening, according to this 6moons review linked to below: https://6moons.com/audioreview_articles/purifi/
I think these modules are available to the DIY amp building community that previously often utilized the Hypex NC-400 modules, companies that configure or assembled these newer modules in modest custom cases for sale at reasonable prices just like they formerly did with the Hypex NC-400 modules and regular established OEM audio amp companies that previously used the Hypex NC-500 and NC-1200 modules in higher quality custom cases for sale at higher, typically $10,000/pair plus prices. In the 6moons review, Bruno Putzeys stated many of the established amp manufacturers like Rowland and others plan on using the Purifi modules in new upcoming top of the line models and continue to use the Hypex NC-500 and NC-1200 modules in current amp models, that will be then positioned as their 2nd and 3rd tier models.
I also haven't heard much discussion on this thread thus far about the newer
Orchard Audio BOSC, now renamed the Starkrimson. These class D modules/amps are interesting because they are offered for sale at only $1,500/pair, they're offered as either just modules for the DIY community or in very small and modest monoblock cases just like a normal finished audio component product, they measure extremely well and they utilize the newer, very fast switching, GaN output transistors. I believe Orchard Audio designs and builds their own proprietary class D modules and that these $1,500/pair monoblocks are currently the least expensive available class D amps utilizing GaN transistors.
Here's a link to a recent class D article on the Audio Express website that's titled "Fresh From the Bench: A Tale of Two Class-D Amplifiers Orchard Audio BOSC and Purifi Audio Eigentakt EVAL1":
It's important to note that both of these modules are a further advancement of the currently available solid state and analog class D power modules technology that accept only analog signal inputs and have regular high-level speaker outputs . These need to be distinguished from the newer technology of digital class D amp modules that will accept only digital signal inputs and have high-level speaker outputs, which are typically referred to as 'power dacs'. These power dacs are likely to become more prevalent in the near future, possibly in new, non-traditional 'integrated' combinations of functions in a single chassis or even digital interconnects to speakers powered by one or more power dacs. Class D continues to improve at a relatively rapid pace
and new paradigm shifts are not only possible, I think they're probable.
Find out yourself sunshine, why should bust my ***** trying to explain to a brick wall. There’s plenty to read here. Educate yourself, 3 pages of it. for you to "try" to understand maybe? https://www.stereophile.com/reference/707heavy/index.html
Throw the old dog a bone and he chokes on it. Georgehifi has clearly stated he is unable to explain how EPDR will impact a Class-D amplifiers ability to drive a load. I hate to say I told you so, but I told you so. Hint to the old dog, there is nothing in that article that relates to Class-D.
Do you even know how to read an SOA graph? I am going to guess no. You don’t understand this graph:
In a Class-D amplifier, the voltage across the device is effectively 0 (or close to it). That means the devices operates on the graph effectively on the left vertical axis at 0 volts. The limitation is pretty much the device current rating. Practically it will be a bit to the right of that as there is dissipation due to RDSon and partial conduction for nanoseconds while switching.
Funny you can find tons of time to attempt to bust every Class-D thread and to chase fusers ad-nauseum, but you can't even put a few of your own words together to explain why EPDR could matter to a Class-D amp. I know why you don't. It is because you can't. You would rather bash Ralph from Atmasphere and others not here to defend themselves with falsehoods. That is not honest behavior.
You have nothing but your ignorance and being a fuser, and your persistence in the future shilling of whatever Class-D project you seem to have, could be with an old OTL maker the way your so persistent with wrapping him in cotton wool.
It seems whenever “Class D” amps are mentioned they brought up a bunch haters. They are relatively cheaper to make and they don’t look as impressive as Class A amps for sure. They typically come in smaller package and are way too light compared to those expensive Class A monsters. Regardless how they sound, they just don’t feel high end enough to some. I have owned Krell Class A monoblocks, BAT tube monoblocks, and Vincent hybrid monoblocks before. Currently I’m breaking in a pair of PS Audio M1200. So far I really like them. Monoblocks sounded better than stereo amps that I agree.
Please come back and let us know after you’ve lived with them, as from what I’m told they are the ICE 1200 modules like @tweak1 uses (he’ll be happy) but with a tube input buffer. Look at the graph and say if you can hear a disconnect of sound signature with the phase shift above 1khz. ( red trace https://ibb.co/NC7sC8T ) like I can with my big linear phase ML ESL’s with Neolith panels
Georgehifi CAN NOT tell people here why EPDR matters to a Class-D amplifier because he does not understand Class-D, he does not understand EPDR, and he does not understand SOA. Given his hate for Class-D, if he truly understood these things, he would be all over this given clear, concise and accurate explanations. He does not, because he can't.
And now you are calling me a "fuser". Anyone here can read my posts and readily see that I am not a "fuser". Of course that does not change the fact you don't understand electricity either. "AC" is not an argument for fuses not being directional. It is because fuses are not directional that AC operation is not impacted. It is NOT a subtle distinction.
George, you are the one that needs to give it a break. You act like the Class-D police and fuse police, yet you don't even understand how Class-D works and you make up facts about Class-D that is not even true. I will stop calling out your illogical and incorrect attacks on Class-D when you stop making them.
George, keep digging that hole. I am not the one spreading false information in a one man crusade against something I don't understand, that is you. If your only refuse is attempted personal attacks, then I suggest you exit this argument which you are clearly unprepared for. It is time to let this Class-D crusade go. You are the knight without a sword riding a lame horse.
After probably at least a year of driving my EVS 1200 direct from my LPM moded Oppo 105, and having upgraded all cables and speakers I decided to reinsert my Audio Alchemy DDP- 1 + PS 5.
It took a solid 24 hours to relax, and certainly sounds better than when I first reinserted it. I meant to hit replay on my 105 before I went out last night, so it wasn't running any signal. At first I was disappointed, but then realized I needed to turn the volume all the way up on the 105, which I did just before heading out last night
Now, the 'problem' is: when I want to play SACD/DVD-As, I have to reroute my cables back to direct, which is a RPITA. What I did before was also hooked up my Marantz HDCD-1 (as a transport) to the DDP-1, and run them separate. That may be what I do again "Back to the Future"
@dchang05 I think some people are threatened by Class D for some strange reason. I have a nicer Class A/B amp than your average 'audiophile' in an Ayre VX-5 Twenty. I also have a 7-channel Class D amp (utilizing Pascal modules) for my integrated HT setup. Just for the hell of it, I hooked up the Class D to my mains. And the difference was less than you would think. No harshness, plenty of 'musicality', tight bass and extremely clean midrange. I listened for several hours this past Holiday weekend and my ears weren't bleeding.
There is a lot of total nonsense posted online regarding many topics, including Class D amps.
Are people threatened? Fearful? Did they just hear a bad setup which no one technology alone can fix? Did they just prefer something else in their case? Who knows.
I have Class D amps ranging from $80 to $6000 retail. They all sound top notch used properly in the right application. Just like anything else. Any new amps I buy in the foreseeable future are likely to be Class D or similar as well.
Does not mean they will be everyone’s cup of tea since personal tastes always vary.
But to diss the technology categorically as not worthy for consideration is just a huge mistake. It is most worthy with a very unique set of advantages and little if any downside, personal preferences aside.
Personally I bless the technology. Just apply it wisely. Nothing new there!
Problems with any amps shouldn’t be fixed by using even more feedback as a fix, it’s a added by the best designers to clean thing up a little and usually just local not global in an already well designed amp.
All the greatest amp designers say it. An amp should be reasonably good spec’d, and to use it just as a clean up tool. And the preference with the best is to use "local feedback" only by the best designers. Not global as being talked about here, and then even including the Class-D output filter in the global loop, what next throw the speaker wire and the speaker in the loop as well, like Trio/Kenwood tried all those years ago, utter sterilized disaster sound.
The first paragraph is true. So is the 1st sentence in the 2nd paragraph. Right after that things go off a cliff...
The fact of the matter is design-wise you start with a class D circuit with no feedback and get it to sound decent and perform fairly well too. Then you add the feedback, but in this case so much that the amp goes into oscillation. With a normal amp you could never get away with this. But with a class D amp, the oscillation is then used as the switching frequency, so you put a few frequency sensitive components in the feedback network so that when it goes into oscillation, it really can find only one solution- one frequency- at which it oscillates. The switching frequency itself is then used as one of the inputs to the amp (the other being the actual audio) but is converted to a triangle wave for comparison to the audio signal.
Now your already fairly linear amplifier has a mess of feedback (over 35dB) too, and the reason for doing this is to allow the amp to compensate for the distortion that is normally generated by the application of feedback. You need over 35dB for this phenomena to occur. This gets rid of the brightness and harshness that is otherwise associated with **all** amplifiers that have used feedback at insufficient levels (which describes nearly all traditional solid state designs of the last 60 years). So its quite unlike that unsuccessful Kenwood system George mentioned above, and yes, you do include the filter in the loop so that the amp can compensate for phase shift induced by the filter.
In a conventional amplifier you have a thing called Gain Bandwidth Product, which is how much gain you have vs how much bandwidth you have. The idea here is that you are going to blow off the gain when you use feedback to reduce distortion (and output impedance). But there’s a sort of zero crossing where the the amp circuit just does not have the bandwidth to support the amount of feedback used. In a nutshell you could say (inaccurately...) that the GBP is a sort of fuel that you use up when you add feedback to the circuit. When its gone the feedback at that frequency is gone too. Put another way, an amp with insufficient GBP will have distortion low at low frequencies and the distortion will rise as frequency rises. This is very audible- our ears are very sensitive at 3-7KHz and they use higher ordered harmonics to sense sound pressure. We’ve been hearing this problem for 60 years and its literally why there are still vacuum tubes around after all this time.
This is why solid state amps traditionally do bass well as there is plenty of feedback to allow them to be low distortion. But at 7KHz there isn’t enough, so harmonics at that frequency aren’t suppressed, and there are actually more harmonics because the feedback is adding them through a process called ’bifurcation’. And so we wind up with an amp that is bright but measures flat. To get around this problem, manufacturers and the test and measurement industry have resorted to a simple technique called ’lying’. The distortion of the amp and the resulting harmonics are measured at 100Hz, where the amp measures quite well. If you measured it at 2KHz you would see something vastly different, which is why that’s never done.
Because a class D amp can have so much feedback, it can measure the same low distortion at 15KHz as it does at 100Hz. IOW the distortion product can be ruler flat across the board. Prior to this technology, the only other way to do this was to have no feedback at all, and use the most linear circuit with the widest bandwidth you could get (200KHz is required to prevent phase shift at 20KHz on that basis). This is all because it really is important to the sound of the amp that the distortion product be both benign (mostly lower harmonics) and ruler flat across the board.
@twoleftears - I actually think that 1KVA toriodal is undersized for a hi-end stereo Purifi amp. I've generally found that using a larger power supply improves the dynamics and authority in the mid-bass and results in a more pleasing sound. I don't know how much this translates to class D designs, but I would expect the same applies.
The Purifi modules' over-current protection doesn't kick in until 25A, so it seems like there's value in using a beefier supply. The DIY Purifi amps I'm building will use a 1.5KVA transformer for each monoblock, although a small portion of this is allocated to the lower voltage supplies.
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