• Re: foreplay power supply questions - m.w.h 12:58:28 01/29/03 (0)
  In Reply to: foreplay power supply questions posted by m.w.h on January 28, 2003 at 14:57:50:

  Done playing with the simulation: Small caps dont smooth the ac ripple as well, it looks like. 4uf is obvious, at 40uf you need to zoom way in, to see variations of .001v, and 80uf its much smaller still, and at 220uf it cant be found at all.

  I dont know if variations of .001v make a difference (in fact I dont know much of anything) but that would probably be an audible problem if anything. And I can find that out the hard way. My worry is that smaller capacitors could have some effect I dont understand, and that the simulation software doesn't show. Like, smaller capacitance means the transformer will be asked to fill them more often. Maybe it will be asked to do too much? Or something worse I cant even imagine...

  It seems like a combination might be good - big electrolytics up front, smaller (and allegedly better) oil capacitors at the end, where the final discharge into the audio circuit happens. In simulation, 220-> 220-> 40uf is as smooth as 220-> 220-> 220uf.

  Sorry for the rambling, just looking for some free advice :)
  
  

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• Re: constant current source - MartinR 09:41:59 01/29/03 (0)
  In Reply to: foreplay power supply questions posted by m.w.h on January 28, 2003 at 14:57:50:

  FWIW, in the PSD, instead of using a resistor at the end, you can change it to a constant current source, which you can set that to 5mA for the stock FP, or 9mA for the C4S'd FP.
  
  

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• Re: foreplay power supply questions - Paul Joppa 21:07:26 01/28/03 (0)
  In Reply to: foreplay power supply questions posted by m.w.h on January 28, 2003 at 14:57:50:

  The most recent (current) Foreplay power transformer has an open circuit secondary voltage of 146v at 117v on the primary, according to my rough and ready measurements. The primary DC resistance is 78 ohms, and the secondary is 221 ohms, so I get 343 ohms equivalent.

  All of this ignores the filament power. Filament current will cause more drop in the primary, reducing the effective primary voltage by about 3v. Yes, the open-circuit voltages scale linearly.
  
  

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• Re: foreplay power supply questions - Jim Carlon 17:29:07 01/28/03 (0)
  In Reply to: foreplay power supply questions posted by m.w.h on January 28, 2003 at 14:57:50:

  OK, I can give you one part, but this will be based on 'book values', so you will have to adjust accordingly.

  B+ at the final filter is specified at 157 Vdc. By using Ohm's Law to analyze the current flow through a few resistors, it is possible to draw the conclusion that the stock circuit, with both channels in operation, draws a total of ~ 5 mA. Ohm's Law again: 157/.005 = 31,400 Ohms load resistance.

  Now, as to the transformer, the specs on the one in my FP indicate a primary voltage of 117 Vac for a secondary voltage of 125 Vac at full rated current on both the high and low voltage secondaries. The voltages will rise with less than full rated currentbeing drawn.

  That's the best I can do, as I have not played with the PSUD, but perhaps it will get you another step down the road.

  Jim
  
  

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