DIY means Do It Yourself. A simple enough statement. It's a wide umbrella which covers everything from someone putting a $4.95 Radio Shack driver into a cigar box to keep the back wave from cancelling the front, to giga systems that would cost more, if bought as manufactured items, than any random three of us could afford if we pooled our resources.
Once upon a time, there was a man named David Hafler. He made his reputation with tube circuits (amongst them the famous Dynaco ST-70, which sold about ninety-nine million units way back when--some people still like 'em), then went on to start the Hafler company. Probably the best known Hafler product was the DH-200, a 100W/ch solid state amp, available as a kit or factory-made unit. A good, reliable, decent sounding unit that went on to sell another ninety-nine million units. I hope David got rich off of them. He deserved it. Good product at a great price.
But for all that it was a separate amp, it was mid-fi. I don't recall a single person who ever felt otherwise. The build quality was excellent (for the price), but the amp tended towards being somewhat harsh on top (a later revision, the DH-220, cured some of the sonic problems) and got positively rough when pushed hard.
The power supply was simple. A standard EI transformer (big toroids were rare in those days) through a bridge rectifier, into a single pair of caps. The value of the caps? 10,000 uF, one for each rail. Now, condsidering that the one power supply took care of both channels, that would work out as being right in line with Slone's rule of thumb for capacitance/watt. Only, the thing was, you could hook a meter to the rails and watch the voltage fluctuate as the music came and went. The first thing most audiophiles did was to tag more capacitance into the amp. Around here they used the Mallory CG series, but in other places they used Sprague or whatever was available locally. It made a huge difference in the ability of the amp to handle peaks...and firmed up the bass. Something even a teenaged kid could hear over a pair of old Advents. He borrowed the caps from his older brother just to see what all this cap stuff was all about. No ego, no preconceived notions, just a couple of borrowed caps and an open mind. The way I heard about it was that the kid brother didn't want to give the caps back when he found out what a big difference it made and the two of them had a bit of an argument about it.
Now, if a curious kid with a ragged-out pair of Advents and a DIY mid-fi kit can hear the difference caps make, it makes you wonder whether Slone ever listens to his stuff, or simply does it as textbook exercises.
Ripple calculations are pretty basic. Within reach of where I'm sitting as I write this I've got ten or fifteen books, all of which will have at least one chapter (or, in the case of Gottlieb, the entire book) on power supplies. In the book shelf on the other side of the room I have another dozen books which will also tell you how to deal with ripple. Kind of them. (Incidentally, for those who might wish for a basic education in electronics [as opposed to Horowitz & Hill, fer instance, which can be pretty opaque to the uninitiated], allow me to recommend the ARRL Handbook. That's the book the Ham radio guys use. No, I'm not a ham operator. Never have been. And yes, there's an awful lot of radio stuff in there which may or may not be of interest to you. But the treatment of basic electronics is second to none in terms of being accessible and practical. Those guys don't have time for a lot of fancy-pants theory, they want a radio that works. There are times when peoples' lives have depended on Ham operators when all other communications have failed due to natural disaster or war or whatever. You can get your theory later from H&H or Diefenderfer or whoever is popular this year. If I'd had the ARRL book when I was a kid, I'd have learned electronics ten times faster.) Anyway, I regard ripple calculations as a good starting point. A bare minimum. To get any performance out of an amp, you're going to need more. Mysterious? No. There's no mystery. When the rails sag, the operating point for the gain devices change, whether bipolar, FET, or tube. When the operating point changes, that causes distortion. (CMRR cannot guard against a sagging rail. That's not what it's for.)
Actually, I guess there is a mystery: Why would anyone defend a circuit that allows dynamic distortions of this nature?
Granted, short of a well-regulated power supply, there will always be some ripple; some collapse of the rails. It's also subject to diminishing returns, as are most things. No problem. But why sit at the bottom of the returns curve with a minimal power supply, when you can slide at least part-way up? (Subject perhaps to having food to eat, spousal-approval-factor, etc.)
Fortunately, there's room under the DIY umbrella for all of us, from speakers in cigar boxes on up. The choice is up to the individual as to how much performance they might want, but to deny that more performance is possible, whether the individual chooses to attain that performance or not, is foolish.
The owner of a Camaro knows that Ferraris are out there, whether he will ever own one or not. His Camaro may even have been hot-rodded to the point where it will accelerate as well as the Ferrari, but will it do everything else as well as the Ferrari? Nope. It's still just a Camaro. But the wise Camaro owner doesn't deny the existence or validity of a Ferrari just because he doesn't own one.
Incidentally, if I had a circuit that required a 60% overvoltage on the rail, I'd start looking back upline to find out where the bottleneck was. Given that it's a car system, there aren't too many places to have to look, although given the limitations of a car's electrical system, some of them may well prove to be intractable.
Grey
