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Re: main cap value on OTL ?

Posted by Lew (A) on February 5, 2007 at 08:54:31

In Reply to: main cap value on OTL ? posted by coresta on February 4, 2007 at 14:13:59:

When I got into this issue some years ago, I got the idea from Ralph, Mark Gilmore, Paul Speltz and others that more is better, as far as capacitance goes in the output supply. In recent years my reading indicates that there is some value in having a small-ish value cap as the first cap after the rectifiers. Paul Speltz combined these virtues by suggesting a CRCRC topology (see the old ASOG Tweaks section), where the first cap is relatively "small" (i.e., <2000uF), the first R is <0.5 ohms (>5W, too), and the second C is similar in size with a smaller R following that, then the final bank of C can be whatever you can fit. In my amps, I use 2000uF/0.21ohms/2000uF/0.1ohms/14,000uF. I listened to my amp extensively before the mod (i.e., with only a very large capacitance after the rectifiers) and then of course since then with the CRCRC topology. There is a real audible improvement with the latter. Make sure you use hi-wattage resistors, if you do this. Even though the voltage dropped across only 0.2 ohms is rather small, the current is very high.

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