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Possible tweak

Posted by Lew (A) on June 18, 2008 at 11:00:01

My MA240s were supplied with huge 7800uF computer grade electrolytic caps to filter the output stage supply, one cap per phase. Several years ago, I increased the total capacitance per phase up to 13,800uF, by adding three 2000uF caps per phase, in parallel with the 7800uF cap, to each monoblock. Furthermore, I incorporated the Paul Speltz tweak of adding 0.21 ohm resistors in series (one each on the positive and negative legs) between the first and second 2000uF caps after the FWBR, and 0.1 ohm resistors in series between the second 2000uF and third 2000uF caps. (The 7800uF cap is the final cap in the paralleled grouping.) This mod resulted in a markedly improved bass response on my Sound Lab M1s, both in detail retrieval and in the apparent LF cutoff frequency, which seemed to go lower by an octave.

In recent years, Panasonic has marketed a line of electrolytic caps which are remarkable for their small size, low ESR, and high ripple current ratings. So I propose to dump the 7800uF cap entirely and to replace all the caps with 2000uF/200V Pansonic TS-ED type lytics. I can easily fit seven of them per phase to slightly exceed the current total of 13,800uF, but even more caps could be crammed in there, though I don't know that adding even more capacitance is going to be as significant as was the change from 7800uF to 13800uF, due to the law of diminshing returns. I don't know whether the Atma factory has glommed onto these caps, but they are only 2 inches high by less than 1.5 inches in diameter and are relatively cheap. I expect that a gaggle of 2000uF caps is going to be "faster" sounding than the huge single lytic.

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