Just to let people know that things are still happening, the brain juices are cooking at the moment ...
It's obviously not a trivial exercise doing an amp capable of high output: one way is to just throw a lot of money at the concept and use brute force engineering to get the job done. This is how the McIntosh MC2KW was built, and I'm not going down that road. At the moment I'm working on getting some of the key elements of the design decided on, and this splits naturally into 2 areas.
First is the power supply which are far as I'm concerned is the key to the whole exercise: if it's not done right then the end machine will be a dud, and not worth the effort. And so far it's either going to be a conventional affair in the style of Krell, without going to the extremes of custom transformers, just off the shelf parts intelligently hooked together; or, a custom switching power supply setup. Off the shelf SMPS's are too expensive, and not suitable in terms of output. Even though Gary doesn't like switchers it can be done properly, the Chord amps from the UK proved this, and if you go into the design aspects there are all sorts of advantages in being able to handle fairly precisely and in a straightforward manner how the interference artifacts are minimised. Also it will be lighter amd more eco friendly! The big downside is that a significant more effort needs to go into getting the initial design right, I'm not familiar with SMPS. But, in contrast, getting a conventional supply to always behave itself could end up being just as much a time consumer: I haven't done enough yet to decide ...
The second bit is the amplification stuff, obviously enough, and here my thinking will be back to front for most people. Unlike most, I'm a fan of feedback, properly done, and both the DIY gainclone and HT box use this technique at the heart of their functioning, and have proved themselves to me. So the real concept of the 2400W amp is a high quality opamp, with tons of grunt, a big mutha of a gainclone so to speak.
I can hear a lot of you out there crying, "Disaster!! Opamps and FB are worse than climate change for a healthy world, and a decent listening session!". Well, I beg to differ: every time you listen to a recording now you're listening to the sound of such technology, it's all about doing it properly. Some very highly regarded amps have used this technique over the years, but it's not politically correct, so they stay in the background of people's thinking. Meridian, Musical Fidelity, Eidetic in Australia have all used it, and I'm sure there are others -- implementation is everything ...
So one way of looking at things is to say, select an opamp that sounds right to you and then hang a voltage and current multiplier to the the back of it, and let FB take care of the audible misbehaviour of the output stage. If this is done correctly then the output stage used becomes irrelevant, it could be an array of gainclones, MOSFET, BJT, class D and it all sounds the same: the signature, or sound of the amp is not that of the power devices, but that of the opamp. Which, of course, should be "transparent", ie, no personality. The opamp, or equivalent, is the master, the output stage is the slave ...
In that sense I'm comparing all of these options: there is where the next quandry arises, dealing with the voltage swing. I'm after 2.4kW into 8 ohms, that translates to a 400V swing peak to peak. Or, 200V power supply rails. A lot of the "correct" audio output devices won't handle this, the ON BJT's only go up to 350V. Almost, but not quite there! So if I want to use a conventional output stage arrangement then I will need to use non "audio" devices, more effort will be needed to make them behave in a reasonably "linear" way. Or I could go to a bridge solution ...
Alternatively, I could go for a effectively completely modular output solution, using assembled class D circuits or power IC units. The problem of voltage swing is even more exacerbated here, and to solve that one has to do, at least as one solution, what has been called a bridged bridge topology. That is, taking 2 amp circuits, bridging them, doing a second such and bridging that combination. Then things get a little tricky, you need floating power supplies and the inputs need to be floated, things like transformer coupling likely come into the picture.
All right, that's enough for now! It gives anyone interested an idea where my thoughts are heading, it's still all about making major design decisions ...
Frank
