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If Low DCR Power Supplies are a Panacea.........

Posted by mach1 (A) on July 4, 2006 at 20:07:24

Then why do so many people out there prefer the sound of tube rectifiers to solid state alternatives which offer dramatically lower resistance ? Morevoer, why do many people prefer the sound of directly heated rectifier tubes over their lower resistance cousins?

I think I would be correct in making the assertion that the difference in series resistance between a 5U4 and UF4007s would swamp the difference between a 30 ohm transformer and a 6 ohm 'ultra-fi' alternative. Similarly, wouldn't the difference in resistance between a 5R4 and 5AR4 be about the same as that beween an 'ultra-fi' transformer and an 'also ran'?

In a 12B4 linestage test mule (ccs-shunt reg-ccs configuration) that I have been messing around with for the best part of a year I have (among other things)observed the following:
1. the sound improved noticeably when I went from capacitor filter to an LC filter (actually there is still a 1uF cap before the choke just to bump the voltage up to minimum required)using a 10H 200R (!!!) choke.
2. After extensive rectifier rolling, I definitely prefer the sound of a good directly heated rectifier to an indirect, finding them to generally offer a more immediate sound in this application with better dynamics and palpability - despite their greater resistance.
3. Differences in psu configuration and rectifier are surprisingly easy to hear, despite the supposed 100db+ isolation offered by the ccs-reg-ccs configuration (if anyone has a suggestion why, I would be interested to hear).
4. Plain aluminium Hammond chassis have an industrial look that can grow on you if you are somewhat manually challenged.

PSU output voltage is not an issue here because as long as the psu outputs the minimum required for the shunt reg all is fine, and any excess voltage produced by more efficient rectifiers is taken up by the first ccs - as far as the last ccs and tube are concerned there is no difference in voltage attributable to different rectifiers.

As an aside, I also seem to remember reading an interesting article by Dan McLaughlin a while back on his 71A 'Quark' in which he made the asserion that the sound improved commensurately with the number of LC sections (8uF oil caps)in the psu. He actually reported a positive correlation between increased resistance and good sound.

In conclusion, while I am sure that in some applications low DCR power supplies will sound better than low resistance alternatives, I not see the achievement of ultra low DCR as a panacea, and question its potential cost-effectiveness.

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