+ Reply to Thread
Page 3 of 14 FirstFirst 1234513 ... LastLast
Results 21 to 30 of 137

Thread: Musings on Class D .... is it actually 'there' now? Should we all be using it?

  1. #21
    Join Date: Jan 2009

    Location: Deleted

    Posts: 6,585
    I'm Deleted.

    Default Musings on Class D .... is it actually 'there' now? Should we all be using it?

    As I understand it the Devialet approach is rather like the Musical Fidelity Superchargers (if you remember them) - they weren't class D but joined with ones system in a similar way. A small low powered Class A amp (remember that most active pre-amps operate in class A) of a couple of watts (probably less) drives a class D stage that does the real amplification. The idea is that the characteristics of class A are reflected in the output but rather assumes the class D stage is doing no harm of its own.
    Last edited by YNWaN; 18-07-2016 at 11:43.
    Account Deleted

  2. #22
    Join Date: Jan 2009

    Location: Essex

    Posts: 31,861
    I'm openingabottleofwine.

    Default

    Quote Originally Posted by YNWaN View Post
    As I understand it the Devialet approach is rather like the Musical Fidelity Superchargers (if you remember them) - they weren't class D but joined with ones system in a similar way. A small low powered Class A amp (remember that most active pre-amps operate in class A) of a couple of watts (probably less) drives a class D stage that does the real amplification. The idea is that the characteristics of class A but rather assumes the class D is doing no harm of its own.
    How does that differ from Quad's 'Current Dumping' technique?
    Barry

  3. #23
    Join Date: Feb 2013

    Location: W Lothian

    Posts: 99,005
    I'm Grant.

    Default

    Quote Originally Posted by YNWaN View Post
    Jez's description of how class D behaves into low loads is how I understood it. Another contributor to this thread said that class D was good with punishing loads but that isn't really the case and power output rarely doubles as the impedance halves - in fact they are rarely good into low loads like 2 Ohms. The specs of my own amp do claim a doubling of wattage into 4 Ohms over 8 (600wpc instead of 300), but any lower impedance than that and output falls off steeply. I think this is likely the reason that class D amps often fail to sound as powerful as their specs would suggest (as Jerry mentioned earlier).
    used mine into my telefunkens that are 2.75 ohms without issue. they are sensitive mind which may make a difference
    Regards,
    Grant .... ؠ ......Don't be such a big girl's blouse

    I've said it before and I'll say it again: democracy simply-doesn't-work
    .... ..... ...... ...... ................... ..... ..... ..... ..... .....
    FIIO K7 BT, M11 PLUS, BTR7, KA5 - OPPO BDP-103D - PANASONIC UB450 - PANASONIC 4K ULTRA HD TV - PIXEL 6 - AVANTREE LR BLUETOOTH - 2* X600 SOUNDCORE - HEADPHONES INCLUDE, FIIO, NURAPHONES', FOCAL, OPPO, BOSE, CAMBRIDGE, BOWER & WILKINS, DEVIALET, MARSHALL, SONY, MITCHELL & JOHNSTON - 2*ZBOOK'S- MERCURY BD ROM, ROON, QOBUZ, TIDAL, PLEX, CYBERLINK, JRIVER - MULTI HDD'S -

    Oh my god! There's nothing wrong with the bidet is there?

    “Nothing discloses real character like the use of power. It is easy for the weak to be gentle. Most people can bear adversity. But if you wish to know what a man really is, give him power. This is the supreme test. It is the glory of Lincoln that, having almost absolute power, he never abused it, except on the side of mercy".

    “You see these dictators on their pedestals, surrounded by the bayonets of their soldiers and the truncheons of their police ... yet in their hearts there is unspoken fear. They are afraid of words and thoughts: words spoken abroad, thoughts stirring at home -- all the more powerful because forbidden -- terrify them. A little mouse of thought appears in the room, and even the mightiest potentates are thrown into panic.”

    "You don't have free will. You have the appearance of free will.”

    “There's a war out there, old friend. A world war. And it's not about who's got the most bullets. It's about who controls the information. What we see and hear, how we work, what we think... it's all about the information!”


    ***SMILE, BE HAPPY***

  4. #24
    montesquieu Guest

    Default

    Quote Originally Posted by Barry View Post
    How does that differ from Quad's 'Current Dumping' technique?
    Presumably in using a Class D amp after the initial stage, rather than one in AB?

  5. #25
    Join Date: Oct 2012

    Location: NE England

    Posts: 4,173
    I'm Jez.

    Default

    Quote Originally Posted by User211 View Post
    Heard a Hypex NC1200 design in my system with SMPS and an Audio Note M8. Absolutely awful. And very recent and very expensive.

    An NC400 design with JFET input stage and no SMPS - best I have heard in class D. A prototype made by Jon Oakey of Reality Audio. I reviewed it on the Wam.

    Avoid SMPS designs at all costs, is Jon's advice.

    Jerry's Crown was quite nice sounding but a bit lacking and didn't "sound" powerful. Actually, nor did NC1200.

    I had that Lyngdorf you had Tom in my system at a bake off. It was OK, not brilliant though.

    The class G/H amp Jerry and I have is very good if slightly veiled. It has a lot of very positive qualities. I really like it and I think Jerry really likes his too.
    Eee so many things to answer but I'll start here....

    A SMPS in effect IS a class D amplifier!! A linear regulated supply is basically a class A amplifier being used to give a DC voltage out, regulation being achieved by comparison with a fixed voltage reference. Same with a class D amp being used against a reference voltage to give a DC voltage out. The high efficiency of a SMPS is achieved in precisely the same way as the high efficiency of a class D amp... as they are the same..
    Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)

    Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
    ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
    Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
    Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco

  6. #26
    Join Date: Oct 2012

    Location: NE England

    Posts: 4,173
    I'm Jez.

    Default

    Quote Originally Posted by User211 View Post
    Class G/H is not similar to class D. So this is a little irrelevant I guess, but some blub from the Apart Champ manual:

    "In the following pages we will explain how we have reached our goal. Champ-One features an
    exceptionally dynamic output stage, a unique combination of class G and H amplifier topology,
    all packed in a two unit fanless enclosure. While our competitors are struggling with often poorly
    designed so called energy efficient class D digital amplifiers…well, we have taken a close look
    and listened carefully to some of these designs, and we were not impressed. We got inspired to
    make something APart from all the rest, and started from scratch.

    Take a look at our new champion with his striking design and powerful set of features that will
    exceed the demands of passionate music lovers as well as system integrators. Designed with a
    continuous 4 ohm, 2 ohm dynamically stable high current output stage, Champ-One will surprise
    you with its sonic excellence and dynamic capacities. Remember, this unique amplifier has been
    developed with the impact of live music dynamics in mind. A true beauty, inside as well as outside,
    but also a beast if necessary."

    This amp easily beats the very expensive NC1200 and SMPS in my book, with a MUCH cheaper preamp than an M8. Massively so. It just sounds waaayyy better than that combo.
    ...and moving on.....

    That quote is 100% meaningless marketing drivel! Class G and H are basically adjuncts to other amplifier classes and can be used with class A, class B, class AB or even class D. It can even combine any of the previous classes! Class G and H (I won't describe the difference between G and H as it's not that relevant to the discussion and means the opposite anyway depending on in Europe or USA) are rail switching topologies. To put it simply a low powered amp is used, say 5W, which can be taken up to being say a 200W amp on peaks only, or when the extra power is required, by switching the voltage rails of the amp to a much higher voltage in synchronisation with the music. This is called commutation. The idea is that say 70% of the time only the low power setting is switched in and so it only consumes the power and gives the heat of the low power amp for most of the time. The first commercial use in hi fi I can recall was the Hitachi "Dynaharmony" range....
    Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)

    Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
    ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
    Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
    Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco

  7. #27
    Join Date: Oct 2012

    Location: NE England

    Posts: 4,173
    I'm Jez.

    Default

    Quote Originally Posted by YNWaN View Post
    Jez's description of how class D behaves into low loads is how I understood it. Another contributor to this thread said that class D was good with punishing loads but that isn't really the case and power output rarely doubles as the impedance halves - in fact they are rarely good into low loads like 2 Ohms. The specs of my own amp do claim a doubling of wattage into 4 Ohms over 8 (600wpc instead of 300), but any lower impedance than that and output falls off steeply. I think this is likely the reason that class D amps often fail to sound as powerful as their specs would suggest (as Jerry mentioned earlier).
    ....and next...

    When I mentioned load sensitivity it should be borne in mind that there can be many types of load sensitivity What I was referring to is the effect of the output filter network on a class D amp. This filter has dual purposes, it is a reconstruction filter to give us a linear audio output and it is also a LPF (Low Pass Filter) to try and remove the severe RF interference output from class D amps.

    The audio output of a class D amplifier is nothing more than supersonic square waves at high level! How's that for the ultimate interference source Much effort has to be taken to prevent it acting as a high power radio transmitter with the speaker cable as the aerial.

    The filter at the output is there to filter out this high power RF and, by acting as a low pass filter, it allows the audio pulse width modulation of the train of square waves to be "demodulated" into audio. The filter is electrically similar to the section of a passive speaker crossover feeding the bass driver, in this case though it's all happening at a much higher frequency with the "crossover frequency" being more like 30KHz. Just as a speakers crossover network must be designed to work into the correct impedance bass driver for a flat response, so must the filter at the output of a class D amp... which is where load sensitivity comes in. If the filter is designed for a flat response with an 8R load then there will be treble drop into a 4R load and treble boost into a 16R load etc.

    Oh and for any engineers cringing out there I am of course trying to keep this simple and I'm referring to generic class D and leaving aside the "ah but's... " etc to prevent this getting too beyond the scope of the matter...
    Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)

    Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
    ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
    Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
    Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco

  8. #28
    Join Date: Oct 2012

    Location: NE England

    Posts: 4,173
    I'm Jez.

    Default

    Quote Originally Posted by User211 View Post
    That said the link I provided to class G/H states that it is more efficient than class A/B but it still quotes 50-70% for class A/B.
    ...once more into the breach!

    The theoretical maximum efficiency for a pure class B amplifier is 78.5%. This never achieved in practice and in the case of a class A/B amp 50-70% is about right... BUT only at maximum output! At lower levels they are vastly more inefficient than this and with a 100W amp working at say 5W efficiency would typically be only 15% or so....

    Class G and H are used to gain greater efficiency and are very rarely used in hi fi amps due to commutation issues. They are most commonly found in big PA amplifiers where they can deliver practical efficiency in the 50 - 80% area and so result in cheaper, lighter and cooler running amps. Class D can deliver efficiency usually in the 85 - 95% area.

    Class G and H, and specifically whichever version one wants to call the switching of different tiers of output devices, (as I hinted earlier, ask engineers from Europe, USA and Japan and you will get differing answers as to which is which between class G and H), has only one particularly interesting application to hi fi and that is to do most of the amplification with a pure class A small amp of say 10WPC and then switch in a tier of output devices in class A/B for the peaks. I'm not sure if any commercial amp has been made along these lines but I'd guess there will be one somewhere....
    Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)

    Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
    ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
    Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
    Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco

  9. #29
    Join Date: Oct 2012

    Location: NE England

    Posts: 4,173
    I'm Jez.

    Default

    ...on to Devialet.

    The basic operating principle of the Devialet amps is that it is a class A amp of a few Watts output being "swung between the rails" sort of class G or H stylee, of a couple of class D amps basically being used as SMPS's (see earlier for similarity of class D and SMPS). This gets a bit difficult to explain here... but a class A amp of say 3W can supply the entire output of say a 200W amplifier providing it can handle the full current delivered to the load. The purpose of the class D amps (which could be class A/B etc) is to keep the voltage seen by the small 3W amp down to the point where it only dissipates the power of a 3W class A amp even at much higher levels. It's not quite a first in that similar things have been tried before and even built, by Technics amongst others, but is a relatively untapped technology... I have my own technology along these lines which I have done a fair bit of theoretical development work on as well but I've not taken it beyond that.... hey it's virtually impossible to get people to buy conventional technology when you're a largely unheard of one man band, never mind stuff that's "out there"

    The beauty of the Devialet system is the use of advanced digital signal processing to control the nitty gritty details of the technique that have proved a bit awkward before they came along
    Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)

    Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
    ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
    Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
    Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco

  10. #30
    Join Date: Feb 2008

    Location: South Wales

    Posts: 9,151
    I'm NotTakingLifeTooSeriouslyTheseDays.

    Default

    Some good posts there Jez!
    A...
    "Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality"
    Nikola Tesla



    Its now a conspiracy theory to believe that the Immune system is capable of doing the job it was designed to do.
    A fish is only as healthy as the water its swimming in ! [Dr Robert Young]


    www.tubedistinctions.co.uk

    Matthew 5:10

+ Reply to Thread
Page 3 of 14 FirstFirst 1234513 ... LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •