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RE: Voltage regulator details

Posted by John Swenson on May 16, 2008 at 15:54:30:
I determined the value of C2 by trial and error! Gary originally had a 100uf cap there. I think the primary reason for the large value was to provide a long time constant for a "soft start" effect. I found that when using it as a regulator it would oscilate like mad during that startup phase. You could hear it in the amp as a tone that would start at a low frequency and work its way up through the audio spectrum and eventually go away. At this value the time constant is small enough that it doesn't go crazy during startup. I left it there!

At very small values (or not there at all) the cascode bias has a high impedance to the output, which causes it to oscilate as well. The 2.2uf seems to keep everything nice and happy.

My shunt regulators I tried were not specifically any one persons designs but a number of variations I came up with myself using both pentodes, bipolars and mosfets and various hybrids of the types. Trying different CCS designs and different shunt circuits. This circuit beat them all sonically and is quite a bit simpler than some of the shunt regs.

John S.