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|14th October 2015, 04:59 AM||#1|
Join Date: Oct 2015
The Amp1 system - no compromises
This is about about my most ambitious DIY project. I call it Amp1 for various reasons. It is not just an amplifier, one can regard it as a DAC with sufficient power to drive a couple of speakers. Some calls this kind of thing a "Power DAC". Here is a picture from my home. The box with the CPU coolers to the left is the left mono block, which is connected to the left of my B&W804D speakers. The right one is hidden behind the right speaker. To the left of the turntable is the "Central unit", onto which various digital sources are attached. The central is feeding the blocks with audio data via data cables - that's the yellow ones you may notice. You may also notice the radio remote control in the bottom of the picture.
For several years ago, I use to ponder the question how one could get the most audio quality for the money, just by using some sort of signal path logistics. Normally, there are perhaps a DAC feeding a preamp that passes the signal to a power amplifier. All connected via usually expensive cables. So I came up with this solution, gradually. The thing is to have as short signal path as possible, and as simple circuitry as possible. One may say that the beginning of the signal -effectively - is the master clock. Before that, there are just a bunch of data. And the end is the speaker terminals. Since each mono block of this system has a stable master clock that acts as a reclocker and makes the system insensitive to jitter, the effective path is about 60cm or two feet. The DAC itself - a PCM1704 - feeds a resistor with it's output current ( +-1.2mA ) and thus generates full output swing. In between there are one mosfet and one folded cascode. That voltage is LP-filtered and fed to a driver mosfet, which drives the power mosfet's that operates in single ended class a with no feedback and has a bias of 6A.
What? 6 ampere? Then the power losses should be up towards one kWatt!
Well, that's intolerable, so I'm using a technique with a second (or first, really) amplifer, run in class AB at around 0.3A that feeds a "virtual ground" to the power mosfets. They are operating on a 12V separate floating supply, and the power losses will be less than 100W per channel.
When I found out this method, I realized I have to use it, it's not too often one has such a bright moment, and a thought "Someone in the world must have invented this before me", a indeed someone had. One day, I read an article by Mr Nelson Pass, that i can't find anymore, and he described that very method, and it was patented since a long time.
When I began this project, I had some entrepreneur ideas about making money on this thing and start manufacturing it. The patent seems to be a US one, and it is possibly circumvented by the fact that Amp1 is single ended - the patent described a push/pull amp. Now I have realized that I really don't want to spend a lot of time on trying to manufacture it, and I don't have the proper know how and the right contacts and I have no nose for business. So I'm now presenting it to you, guys, as an advanced DIY project. Then we don't have to worry about patents, do we?
From my point of view, a good piece of equipment comes from a solid base of philosophy. Rationalists wouldn't approve of this thing, the would argue that a good amplifier with properly designed feedback, distorts less than what the human hearing is able to detect, and speaker cables and such, has no effect on sound, so the Amp1 is to them simply overkill. Rationalists always tells us that this and that is beyond human hearing, have you thought about that? On the other end of the scale we have those constructors that listens carefully and spend a lot of time on "voicing". That's not my approach, I think the placebo effect shows up frequently, and the constructor goes round in circles, but some very good amps are made that way, but I don't have that kind of capabilities.
So, from my philosophical point of view, what can be better than a stable master clock that feeds a state of the art DAC, which in turn drives a couple of mosfet's, where the output devices are operating in single ended class A at 6 ampere bias current? Regardless of price?
So, this is really a simple thing - max value for money.
I talked about those who "voices" their amplifiers when they develop them. I cannot really see how Amp1 could be "voiced", it's so simple that there aren't any parameters to play with. The circuit itself is quite complex, but it is all the surrounding circuitry, such as several current sources and other things that makes it complicated. The signal path is very simple, as you can see for yourself.
OK, how does it sound? Well, constructors usually don't want to talk about subjective matters, but I will tell you the following.
Before the Amp1, I had some really good audio gear, but when I first auditioned it, it sounded very inconspicuous and toned down, but after a while and I relaxed in my sofa, the charisma started to grab me, and it started to open up, and I realized that the champ had installed itself. No more talking about this, but I will tell you one thing I experienced. If the volume is a bit up, but not too loud, and some click or pop or some other abrupt sound appears, one twitches and looks around in the room. The realism is so strong that you really can't believe the sound came from the speakers, it must be something that falled to the floor in the room.
OK, I have a lot of other subjective impressions but will hold them for myself. I don't want to fool people into building something that won't live up to their expectations. But I think most of you can judge whether this system has some potential or not.
I have attached some pictures and a block diagram and circuit diagrams for the analog section.
I wan't to inform you that the hardware costs around $1500 to $2000 if you buy the parts on Farnell or Mouser or similar. The system is equipped with two DSP' and four microcontrollers. If someone is interesting in building this device, please take contact, so I will start tidying up the documentation and fix bugs in the PCB's. The system is in a typical prototype state, as you can see in the pictures, and things must be sorted out a bit. The software is pretty stable, and you may get a copy of the source code, or perhaps the binary data. You will have to have a programmer for Microchips controllers, or I can send you preprogrammed devices in an envelope.
I have a simple site where I use to document various stuff, such as amplifiers and DAC's.
If you have any questions, please email me. My address is found on my site.
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