If I understand the data pages for the various diodes correctly, VF (Instantaneous Forward Voltage/forward voltage drop) is the specified voltage drop for the diode. If this is the case, comparing them reveals the following:
Diodes Inc. 3A, 20V Schottky: 0.475V @ 3.0A @25oC
0.850V @ 9.4A @25oC
Fairchild 8A, 1200V Stealth: 2.8-3.3V @ 25oC @ 8A
FRED 2.7-3.1V @ 125o C @ 8A
IXYS HiPerFRED 15A 1200V: 1.79V @ 150oC @ 15A
2.75V @ 25oC @ 15A
IXYS FRED 12A 1200V: 2.1V @ 150oC @ 12A
2.7V @ 25oC @ 12A
The warmer they are and the less amperage they receive, the lower the forward voltage drop in the FREDs. When graphed, the voltage drop increases exponentially with current, with a concave curve. So, if used at a small percentage of their rated amperage, the voltage drop should minimal, although its rise will be very quick. This means using a FRED rated for far greater amperage than necessary may resolve the voltage drop issue. I am hoping the 15A HiPerFREDS I will be using (along with the 4.3V coming off the transformer) won't cause an issue with low voltage for the H+. I can lose about 1.3 V.
Schottky's exhibit a very steep convex rise in forward voltage drop with amperage meaning very little inital change with the current, although with increasing temperature, they will become less efficient. I wonder if the Silicon Carbide Schottky's would improve performance? I have read many posts to the contrary, actually.
This temperature and amperage data highlights the dynamic performance stats of all these passive pieces in a circuit. Yet another variable/dimension the designer must consider! Not to mention the explanation it provides for change in character (usually for the better) of electronics with a warm-up, as I am sure every good designer would want peak performance at operating temperatures. For example, I find the Piccolo requires about 1/2 hour warm-up before an edge to the treble diminishes.
Whether this modification is overkill obviously depends on the resolution of your system. Tubes found that the change was below his audible noise floor. I have no idea yet whether this will have any audible effect in my system. If I did, I probably wouldn't do it. It is a type of gambling, and the cost of losing (or breaking even) is negligible, or perhaps even positive - a few bucks, a few hours and a few beers... and you can always go back. If you win on the other hand, I can think of no greater satisfaction. It's hard to find a reason not to do it!
If I end up with a component that can rival the very best, but can't yet appreciate due to other bottlenecks in the system, it seems, given the cost, to be a worthwhile investment. Put another way, if I have a component that I am quite sure is not going to need further modification, that is comforting to my obsessive need for perfection; I can direct my attentions elsewhere.
In fact, this is why, despite not knowing the difference between a resistor and a capacitor a year ago, I decided to build some Hagerman kits in the first place. I could see no other way of achieving the kind of performance I was interested in, short of putting down at least $5,000 per component. It now has become an addiction. I now understand the term audioholic"". Whereas before I was just a music lover who wanted good sound, now I'm a music lover who wants good sound and who's obsessed with building my own components (facilitated of course by Hagtech) and modifying my existing system. It's comparable to lusting after a Ferrari, then realizing that for a tenth the cost you can buy the blueprints and build one yourself. Given the amount of forums dedicated to the topic, my situation is not unusual.
Anyways, I'm keeping the cornet stock until I have it up and running smoothly. Then I will start the mods and post accordingly.
