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In Reply to: Re: Being one of those 'hard nosed' non belivers ... posted by rdf on March 9, 2007 at 10:16:48:
"All that said, I have benched and measured a low-DCR test mule and tuning the first LC section – in this case 0.07H @ 3 ohms into 6.8uF - easily doubles the supply stiffness. It’s an approach worth investigating."Some questions, please.
Doubles the supply stiffness compared to what?
What is "worth investigating"? Tuning a supply? You do understand that that is nothing new, right?Thanks, Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
"Doubles the supply stiffness compared to what?
Compared to replacing the 0.07H/6.8uF pair after a SS bridge (in this case) with the typical large value C. The supply is LCLCLC, last two L are 0.6H/11 ohms, last two C are 100uF oilers. The supply runs ~250 VDC loaded with a 5K resistor. To test stiffness another 10K is dropped across the output. The resultant drop in voltage displays an unambiguous minimum over a small range of first C values right around 6.8uF in this test mule. 50% divergence in either direction about doubles the voltage drop.
"What is "worth investigating"? Tuning a supply? You do understand that that is nothing new, right?"
Not sure what you mean by 'tuning' in this context. This first LC is 70 mH, 6.8 uF, well outside the range of any technical documentation I could find. Pointers to references covering this kind of supply appreciated. SMPS?
Thermionically addicted.
I get different results than you. With the 6.8uf in place there is a 25 volt drop increasing the current from 100ma to 150ma. With a 100uf in the C1 position there is an 8 volt drop.Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
PSUD is a godsend but has its limits. Oddball circuits like this push past. With a small L followed by sub- 0.1uf C it's possible to simulate kilovolts from a 200 VAC transformer. It's still useful to put you in the ballpark though, try 14uf. The transformer's secondary is 23 ohms per winding, 209 VAC. I get just over 6 volts from 70 ma to 130 ma (30 ma per SE output tube doubled, 10 ma constant for the two drivers), about 8 1/4 for 100uF. Again, in the ballpark of the measurements. My old EE prof used to tell us calculate for within an order of magnitude of the target and tune the rest by hand. I never bought a product he designed though. ;)
Thermionically addicted.
The problem is that the supply in your sim is not well tuned (sorry, Henry.) My guess is that rdf's transformer and first choke have DCR different from the ones you used.For a given T1 and L1 (DCR included) you will find that there is a specific value of C1 that not only maximizes the output voltage, but also maximizes the supply stiffness (i.e. minimizes the step in voltage when the current is stepped.) Try playing around with the value of C1 in your sim. When you find that value I'll bet that the change in output voltage when the current is stepped will be smaller than 8V.
FWIW, according to the simulations, a second stage of low L low C filtering can improve stiffness further, though the optimum value of C2 is not the same as C1 even if L1 and L2 are identical. Around 3x in the cases that I've played with. I haven't seen much of an improvement with a third stage, but it could be I haven't found the sweet spot.
In any event, I'm talking about simulations. Finding the right tuning (sorry, Henry) in a real circuit might be a real challenge. rdf reported measured results. He wins. :)
-- Dave
Hi rdf,Have you heard the supply ?? Do so !!
I'd personally would wanna add two more 100uF of oliers, and connect them to your existing 100 uFers, in SERIES, ( so you can HEAR 50 uF or less in C's ), and tell us how it sounds playing music, which is the goal of all this.
Use heavy wiring and / or multiple paralleled clip leads from the rectifier to the end of the filter chain.
I'd really prefer listening to the .32 HY Ls over your .6HY/11 ohms ones, due to its smaller core, having less of an effect dynamically upon the amplifier. This is another case where smaller is better. As a guide, over 1/2 a Hy is too big. Over 50 uF is too much C.
Great to hear people are OPEN to experiment and listen. Progress is being made. We will soon be out of the dark ages and using techniques that flat-out work well, quite well, which is all that matters IMHO.
Jeff Medwin
The amp it's going into has 40uf oilers so that's easy. I can also parallel the chokes for ~0.3H at 5 ohms for a taste of both, then decide what direction to go in. Juggling it, two other amps and work at the moment. Not that I'm complaining about the first two.
Thermionically addicted.
Thanks for the update.Well, in the case of paralleling chokes, the "numbers" you quote are correct, but we still have too much core and wire, twice as much !!!, hence the Triad C-40X suggestion to all. I also used 40 uF Cs on Greg's output stage !!
Jeff Medwin
and what hes done is not the supply we are advocating. He was just doing some low L1/C1 experimenting, won't get ya to heaven that way I'm afraid. At least he mocked something up and tried ! Bravo for him.It has to be a total approach to the supply parts, wiring, and to the amp. I've spelled out the supply here this month fairly specifically.
Jeff Medwin
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