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Thread: class D or not class D

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    Default class D or not class D

    I'm deciding over Christmas (or whatever your preferred celebration is or isn't this time of year) whether to commit to building some audiophile grade class D amplifiers. Now that good quality circuits are being produced, with competent components, the advantages of class D do seem convincing.

    My present system includes two Cambridge Audio stereo amplifiers, feeding some Usher floor standers in bi-amplification mode. The improvement, to my ears, was there, but not great, better clarity, and better dynamics, but not by much. I am wondering whether the bi-amping is that much of an advantage, or whether two mono amplifiers might give the same, or better sound.

    The advantages of the class D amplifiers (based on the IR AUDAMP7 design) includes full control of parts, lower transformer power ratings, smaller cheap heat sink (which they call a spreader) and shunt feedback, which I believe sounds a lot better than series (the input and feedback signals are combined at the negative input to the amplifier). As I want to build a phono amplifier using shunt feedback over three stages, I could have a system with all parts shunt feedback (except the x1 buffer stage, which has no feedback, and still not complete, as I have lost the matched quad of FET's, which were expensive!).

    The class D amplifier has analogue control and feedback, so is one of the better designs. Pcb for the amplifier is $8 only, and the PCM controller is DIL, rather than SMD as in my sub bass amplifiers (also to be made next year). Also required will be the simple linear power supply (nothing fancy, just big caps (about 0.01F per rail) and a soft start circuit. All parts available, but not from one supplier!

    The output from +/- 56 volt rails is 125 watts into 8 Ohms, 250 W into 4, and 380 W into 2 Ohms! Efficiency above 80%, so a 300 VA transformer should be adequate, and although I have two tweeters (one ribbon super tweeter) in parallel, which may present a 2 Ohm load, I am not expecting to pump out 380 watts into them, suffice to say it's reassuring to know the amplifier is 2 Ohm stable.
    cheers.....Bryan

    http://qualia.webs.com/

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    Seen this Bryan? Just won best hi-fi innovation in the AVTech media awards. The 120 is the entry level and is 120W. Packaged with their own brand Atohm GTI SE 'speakers it's 6,290.

    http://en.devialet.com/devialet-120-en

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    can't see anywhere where they say it is class D, but there is a little diagram on the amplifier, I think showing the output filter associated with said class D. But this amplifier seems to be majoring on the digital side of things, whereas class D is not digital, although the output (pre-filter) can be said to be pulse width modulated. Although those who understand how a class D amplifier works have said all along, that class D is not a digital amplifier, and D does not stand for digital (its just the next letter available in the class series) it looks as though most people are going to equate class D with digital, which is a shame. A bit like still calling modern styli 'needles', which haven't been used since the days of the 78!

    ps looking at the diagram on the amplifier again, the tiny circuit diagram is of the mains voltage input filter, not a full bridge class D output filter!

    I read somewhere recently that the author thought that class D was here to stay, but at the elevated audiophile level, transistor A or A/B, valves and class D would all exist together, for a long time to come. A bit like direct drive, idler drive and rubber band turntables, or MM, MC and MI or Decca cartridges, moving coil, electrostatic or ribbon loudspeakers, etc...
    Last edited by cat's squirrel; 17th December 2014 at 14:06.
    cheers.....Bryan

    http://qualia.webs.com/

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    I didn't say it was class D. Your posting about building an amp brought this new development to mind.

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    I think it has to be class D, it's in-line with the ethos of the design, and for 250 watts (minimum) any other class amplifier would need significant heat sinking. But I may be wrong...
    cheers.....Bryan

    http://qualia.webs.com/

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    To my mind all the Class D amps I've heard have been marmite, people either love them or hate them, doesn't seem to be a middle ground, they have a lot of bass grip, but for me the top end can be a little fierce, and overall they can on the whole be a little dry for some tastes, but given your penchant for tinkering, and the low cost, ie simple circuits, simple power supplies and very little heat sinking required I'd say go for it Bryan, those who like Usher speakers seem to like them with Class D too, and a lot who like both tend to have a similar taste to yours in music, so perhaps they will be right up your Strasse.

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    Why would you want a class D in anything other than say a smart phone? The design is to be as power efficient as possible, i.e very loud for a small power source. You'd have to do all kinds of fancy switching trickery to get anything hi-fi from one.

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    Quote Originally Posted by qube View Post
    Why would you want a class D in anything other than say a smart phone? The design is to be as power efficient as possible, i.e very loud for a small power source. You'd have to do all kinds of fancy switching trickery to get anything hi-fi from one.
    I think the appeal from a HiFi pov is that they are relatively easy to DIY, and therefore hold an appeal, ie 400w S/S amp requires some hefty components and is a tricky build, 400w class D on the other hand is a simple circuit with few components. All this leaves aside the SQ, but as I said above some people love them, I'm kinda agnostic on them in that I don't dislike them per se, just that I much prefer other ways of doing things.

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    Quote Originally Posted by qube View Post
    Why would you want a class D in anything other than say a smart phone? The design is to be as power efficient as possible, i.e very loud for a small power source. You'd have to do all kinds of fancy switching trickery to get anything hi-fi from one.
    Class D amplifiers are increasing in fidelity quite rapidly, and a long way from the first generation offerings. Most of the hard work is done in one integrated circuit package, and with just two same channel FET as output, there is little for the DIYer to do. The heat thing is a consequence rather than a design goal, and as most of the cost of an amplifier is the large metal bits, a cheaper product can be made compared with other classes of amplifiers, or tube/valve offerings.

    The only real thing to be decided is whether one can hear any difference, and if there is, whether one can live with it. Don't forget, transistor amplifiers (Germanium!) were frowned upon by the valve brigade (and probably rightly so) but they are still with us, albeit in silicon guise. Some unbiased commentators suggest all three flavours (valve, sand and class D) varieties of good quality products will exist side by side for some time to come.

    But horses for courses...
    cheers.....Bryan

    http://qualia.webs.com/

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    Is a T-amp class D?

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    yes. It is a trademarked class D, by Tripath. What a lot of nonsense.
    cheers.....Bryan

    http://qualia.webs.com/

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