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
By the way, if you are using a toroidal transformer and you use metal
plates or bolts to secure it to the chassis....you are closing down the
sound. You want your toroidal transformer off the chassis on a piece of
wood an mounted using tie wraps and glue or a wooden plate on top and
teflon screws......way better sound.
Just a FWIW: the problem you are addressing here is the mounting. Most toroid transformer manufacturers supply mounting hardware, and if you use it the transformer will run hotter than it should. This is because the mounting bolt is steel, its magnetic and while a toroid is supposed to contain its magnetic field very effectively, in practice it does not, so that bolt becomes a magnetic short. If you install one just for fun, you'll see that the bolt is running hotter than the transformer. The solution is really very simple: just use a stainless non-magnetic bolt and no worries. And does this sound better? Yes it does- we discovered this phenomena about 25 years ago and its a nice tweak to any amplifier- the sound will 'open up' a little and of course the transformer will run cooler and make slightly more voltage- both audible and measurable!
Yes, but none yet "so far" that have taken the full major advantage of
the 1.5mhz switching speed on offer when GaN Technology is used
Actually GaNFETs and MOSFETs are both capable of switch far faster than the switching speeds seen in all class D amps including Technics. The problem isn't how fast the devices are! Its how much noise is created (or not) by the switching at power; how much RFI is created, how much of this noise is then affecting other parts of the amplifier circuit, and then there is the issue of the 'body diode', which is where GaNFETs actually have the advantage over MOSFETs. This gets a bit technical, but has a lot to do with the coil in the output filter, which stores energy and then has to release it. Essentially its what is called a 'flyback' voltage (named after flyback transformers in old analog TVs), working in a manner similar to that of a spark coil in a car. In a nutshell, the output device can behave oddly- you tell it to turn off and it won't, partially due to capacitance effects on the gate of the device and partially due to the body diode of the device, which is a primitive diode formed in the passive layers of the device when its made (and I am vastly over-simplifying in this regard!!). The filter coil flyback voltage can be effectively used to kick the GaNFET into its off state. That's a more important reason to use them than their speed, since MOSFETs have made so many gains in the last few years.
An important reason to keep the switching speed a bit lower is dead time. Dead time is invariant with frequency- no matter how fast you switch or how slow, the minimum amount of dead time you will need stays the same. So as you switch faster and faster, the output device is waiting for a greater and greater percentage of its ON time. This causes distortion to go up. Its true that Technics has a faster switching time, but it does not seem to be doing them any good IMO as they are paying the price in several different ways- increased cost without increased performance due to the associated issues with speed.
I think the Weiss op amps could be worth a try. From what I've read, these are the best discrete op amps available and have the ability to bias the output stage fairly high (adjustable with a small trim pot). I plan to use these on one of the input board designs I will build for my DIY amps.
My experience with the Sparkos op amps is that they dulled the sound a bit to much, although did add a bit of welcome body (this was on a hypex amp). The Sonic imagery op amps were very clean sounding but sounded a bit thin and sterile in my system.
Can't loose then with 30 day trial, just like getting any Schiit product 14 day trial. Be nice if Technics did it with the SE-R1, but to even buy one of those is very hard.
So....I think I'll buy a VTV Purifi. I suspect I'm heading for disappointment again, but there's a 30-day trial so why not? Maybe I'll be wrong this time and I can convert over to class D. I have an all-tube preamp currently. I assume the tube buffer option isn't worth it but what about those op-amps? If all they do is impart color than I can rely on my pre. Is the custom input board worth it?
What about Techics GaN based class D amps, are there others who use GaN?
Yes, but none yet "so far" that have taken the full major advantage of the 1.5mhz switching speed on offer when GaN Technology is used, that Technics does with the 188lb SE-R1 that also uses linear power supplies, input ones are regulated.
@ricevs - Thanks for the offer, but I think there is lots of low hanging fruit to focus on before attempting to modify the Purifi module. At some point, I might consider it.
As I keep saying.....everything makes a difference. There is no Class D sound. For instance.....every amp that uses the Purifi modules will sound different from each other. It is not just whether the power supply is linear or switching.....for a great switcher will beat a not so great linear. Every single thing has to be tweaked to the max. The input stages, the regulators, the wire, the connectors, the jacks, the fuses, all has a sound.
By the way, if you are using a toroidal transformer and you use metal plates or bolts to secure it to the chassis....you are closing down the sound. You want your toroidal transformer off the chassis on a piece of wood an mounted using tie wraps and glue or a wooden plate on top and teflon screws......way better sound.
Here is something really important: All Class D amps use a filter on the output to filter the around 500K switching frequency. Without this series coil and shunt capacitor your speaker would fry. It is common knowledge that you would never want your mids and highs in a speaker to go through a ferrite core coil. (Most speaker crossovers use coils, caps and resistors.......for coils the choice is either ferrite core or air core). No high end loudspeaker uses a ferrite core coil in the mids or highs......bass....yes.....everywhere else it degrades the sound noticeably.....
So, why is it that all class D amps use a ferrite core coil on the output of their amps? Why would you want to mess up the sound with a ferrite core coil? You won’t if you value sonics. However, class D was made to be small and efficient and an air coil coil would be too large, and too expensive and possibly radiate more rf.......so, they are never used.......except for NOW. On the mods I do to the Purifi module I change the stock ferrite core coil to a custom made 12 gauge OFC copper coil. This sounds way more open and real then the stock coil......this is a breakthrough. You see, every class d amp that any of you has ever listened to has a ferrite core coil on the output. By the way, only the best air core coil will beat the stock coil. You have to listen and test and listen and test. I also use better sounding caps to ground on the output of the coil and orient these caps so that their outside foil is towards ground, for best sound. I also bypass the output stage power supply with my modified Wima caps for faster and cleaner sound. These caps are also oriented for best sound.
No class D module is "pure" or has not sound. All are compromised. No class A amp is "pure" or has not sound. You start with the best circuit....and tweak it to the max. This is how you get great sound. Using regular integrated circuit op amps on the front end will not get you the best sound. I even modify the discrete circuits and regulators I use. This game in infinite. What is best today is tomorrows boat anchor. What I try to do is create products that are so good for the money......you can use them for years without finding a boat to mount it on.
I just now thought of this. If you are building a Purifi class D amp and you want the mods I do to the output boards then I can do them for you. I will have to figure out the price. Call me if interested.
one more vote for PS Audio Stellar S300. I was a bit critical with that amp in the earlier thread ("Time to buy a class D amp?"). This was my first class D amp, and I switched from pure tube setting. More importantly, I used it with PS Audio Gain Cell pre/DAC, and none of the units, as it turned out, had enough burn-in time. Both units (Gain cell especially) needed almost 400 hours to perform at their best. Now I think that the combination is quite good, not only S300 is a good amp, but Gain Cell is a decent preamplifier, especially relative to their prices. As part of my secondary audio system, I am quite pleased also with the pre. It has a characteristic that do no posses top level pres, it sounds good on old (relatively poor jazz) recordings, that I really like for my secondary system. Its DAC is not as good, it remained a bit harsh and rough, I use an external DAC with it.
Having auditioned a number of class D amplifiers since the earlier thread, my general opinion on class D has been changed. For me, it is clear that this is the future of the amplification, and there is not much one can objectively complain about them, in general. I like also tube amplifiers, just like I like some old car designs, but I think this is more a matter of teste, there is not much of objectivity there.
You have much better price, less energy consumption, less weight, less hit, and better sound. Would you be willing to spend 10 times more to get something that is "apparently" a bit better only in some aspects and worse in the rest?
@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.
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.
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!
@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.
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"
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.
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.
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.
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
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.
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.
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.
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
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.
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.
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.
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.
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.
@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.
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.
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.
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).
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.
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.
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 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.
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.
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