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Old 14th September 2008, 10:17 AM   #11
SY is offline SY  United States
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Pity about that; Italy has so many great grapes that it does better than anyone, why grow something French? Whenever I taste an Italian cabernet, I think, "What a waste, this could have been Sangiovese (or Nebbiolo or Dolcetto or...) instead of another me-too wine."

In any case, I'm almost certain that this is an oscillation problem. Make C3 larger (30-50uF), and if that doesn't cure it, remove C1.
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Old 14th September 2008, 11:09 AM   #12
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C1 removed, C3 replaced with 47uf.....and still the same results....Vout is dropping with a reduction in Vin.... and i have lost some sleep because of this.... perhaps i should forget about this and do with a simple CLC, be happy with it...
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Old 14th September 2008, 11:24 AM   #13
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I've used dozens of Maida-style regs, generally with no (or very straightforward) issues. The performance is good enough that I'd advise not giving up yet. Make sure that the MOSFET and regulator are still intact. With power off and everything discharged, check for gate-to-source, gate-to-drain, and drain-to-source shorts, and check that the regulator chip isn't shorted input to output. When problems occur, solid state devices often transmute silicon to carbon.

Assuming no shorts, with power on, CAREFULLY measure the voltage from output to adjust pin and verify that it's 1.25V.

And the parts are cheap enough that I'd probably replace the MOSFET and 317 anyway.
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Old 14th September 2008, 11:35 AM   #14
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One more thing- in Giame's design, the output-to-adjust resistor is 1k which is pretty high. That's probably to limit dissipation of the 180k set resistor. Unfortunately, the regulator will be unhappy if you're not drawing at least 5 and more likely 10mA. So be sure that you have a dummy load on the output that will pull at least 10mA.
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Old 14th September 2008, 11:53 AM   #15
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I added a note in the website about the minimum loading for the regulator
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Old 14th September 2008, 12:12 PM   #16
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I wonder if that's been his problem all along? There's definitely some variation among 317s for minimum current; most are fine at 5mA, but some (maybe fakes?) need 10, which is a lot for a preamp reg.
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Old 14th September 2008, 03:13 PM   #17
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more work and will be back to update.....
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Old 20th April 2009, 02:14 PM   #18
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Try adjusting the value of R1 (lower)
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