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In Reply to: RE: Dual PS - Worth the Trouble? posted by Triode_Kingdom on June 16, 2016 at 15:15:54
We're rebuilding an ST-70, and I'm trying something a little new, at least to me. We going C-(LR)-C-(and then...
For each channel there's: An isolating diode and an additional filter capacitor. I wanted to retail the choke. The resistor is there because we're replacing the vacuum rectifier with solid state rectification. The idea behind the "isolating" diodes is that if one channel has a nice big bass note, say, and the rail voltage drops, that channel's filter cap can't draw current from the other channel's filter cap.
Will let you know if we think it sounds better than our current mod.
Follow Ups:
" The idea behind the "isolating" diodes is that if one channel has a nice big bass note, say, and the rail voltage drops, that channel's filter cap can't draw current from the other channel's filter cap."
Several things to consider... Unless the time constant of each channel's filters is very long, both will be depleted anyway. Second, most low bass is monophonic. Both channels are taxed more or less at the same time by the program material itself. Finally, if the supply is sagging so badly that operating points or distortion are materially affected, what's really needed is a better supply. Just food for thought.
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Buy Chinese. Bury freedom.
The time constant is very long.
It's (C=100uF)-(choke-resistor in series)-(220uF)-
and then 2 x (diode-220uF).
And while nothing will totally eliminate the voltage drop you describe, this should "all but" eliminate it. Time and our ears will tell. If it doesn't make a sonic difference, it will have been an interesting experiment. If it does improve the sound, it will become part of our standard rebuild.
"The time constant is very long. It's (C=100uF)-(choke-resistor in series)-(220uF)- and then 2 x (diode-220uF)."
You've forgotten the impedance of the load (amplifier). That's what drains the supply and determines the time constant. That aside (and in addition to the points I made previously), the diodes will degrade the ability of the supply to maintain voltage at the channel driven hardest. If this happens, does it really matter if the other channel continues to operate unaffected? The channel producing the majority of the sound will fall on its face sooner because it doesn't have access to all the capacitance of the supply. As for sonics, I wouldn't waste the time. The unwanted effects of the diodes can be easily quantified with basic test equipment. Sorry, I know that's not what you want to hear, but this modification will perform in a way that's entirely predictable.
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Buy Chinese. Bury freedom.
Since what we're adding is extra filtering, I don't think we're increasing the impedance of the power supply. But as you alluded, we'll try it and see. If it doesn't sound good, out it goes.
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