Got a few more moments with the mystery amp today... this is an interesting point in the build of this (or any) amplifier. For those of you who aren't amp builders, you might not realize that everything you see completed in the photo is just the power supply, chassis and hardware. The actual amplifier circuit or parts are not yet there. In fact I could use this to build several different kinds of amplifiers, or at least, several different variations of this one.
The process is the same on every amplifier...
1) Install the hardware onto the chassis
2) Establish your ground path. In this case - a single straight 10AWG piece of copper about 10 inches long located in the exact center of the amplifier and terminated to the earth ground lug on the IEC connector also located in the exact center of the amplifier. This sets the stage for a mirror image layout where all wires are equal length from side to side throughout the entire amp.
3) Wire up the transformers to get all those long leads out of the way
4) Install the main power supply caps
Then stand back and begin to plan your next move as I am now.
Some insight into this power supply which as you know came from the development of the Zen TORII Mono's. It is unique and Zen like in it's simplicity - part of the appeal to me, but it's the performance that really matters. My wanting to continue exploring it is the motivation for this amplifier.
What makes this different are all the things that are missing. Typically you have a tube rectifier converting the AC into ragged DC which is smoothed with a capacitor. That makes it somewhat less ragged, but it takes more. Either a choke or a large high wattage resistor is needed followed by another capacitor is what it takes to complete the smoothing process enough to work with. Of course these steps are repeated further down stream to continue reducing the AC ripple to a point where it's nearly gone - the same as battery power. So the high wattage resistor and additional capacitor are repeated a minimum of once for each additional stage in the amplifier, usually twice.
The result of adding the chokes or high wattage resistors is limited current and reduced voltage. Any amplifier designer will tell you that where good power supplies are concerned you always want as much current as you can get. And if you're new to tube electronics, the picture above will have more to do with the sound of the amp than the actual parts used to create the amplifier circuit itself. The quality of DC power being delivered by the supply determines the quality of the amplifier and the resulting fidelity. So you can imagine how a preamp stage being 3 to 4 resistors and or chokes away from the power source will greatly rob current flow. This hampers dynamics. There is also a delay in time for the current to pass through these filters which can have profound effects on the transparency of your amplifier.
By replacing the current limiting tube rectifier with high current fast recovery diodes we eliminate the current limiting, the voltage sag, and of course a massive amount of heat. Normally tube rectifiers sound better but that is in the context of using 10 to 100 microfarad capacitors. When you use a 2000 microfarad capacitor that's the size of a milk bottle the game changes and the tube rectifier becomes the clear looser in this contest.
Using such a large cap stores so much energy that it becomes a black hole for all AC ripple and noise on the line. It eliminates the need for a choke or a large high wattage resistor with additional capacitors.
That give us zero current limiting and zero voltage loss and zero heat. It's a win, win, win.
Of course to feed the preamp stage (smaller tubes) we need to drop the voltage and the common way to do that is a high wattage resistor followed by a small capacitor. That is how the Torii Mono's were done. In this amp, I am replacing this resistor with a vacuum diode aka voltage regulation tube (OA3) which will give me the same voltage drop as the resistor but with 20 times the ripple reduction and 100% decoupling so that harmonics from dirty power grids in your city do not contaminate the pure DC power feeding your critical preamp stage. This also means that again 100% of the heat has been eliminated.
This will be the first power supply I've ever done that has zero resistors and zero chokes. It's so Zen it's scary.
Steve ;)
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