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In Reply to: RE: Voltage regulator details posted by John Swenson on May 14, 2008 at 13:59:17
Hi John,
Very elegant circuit! And as elegant an explanation, though I was wondering about how you determined the value of C2. I've tried simulating rejection vs frequency and noticed there is some play between the various time constants in there. To be honest, I'm getting some slightly odd results and need to double check my sims and mosfet models.
Did you try the circuit without C2 at all? Wouldn't be a cascode at ac without it I suppose, as the load is on the source of Q1 rather than the the drain of Q2.
Also wondering which shunt regs you'd compared your circuit to; I've contemplated Emile Sprenger's and (similar) VSE the Camille designs, but yours would be far less hassle, not to mention efficient. Thanks very much indeed for sharing this one!
Best,
Chris
Follow Ups:
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.
Good old fashioned empirical approach then!
Thanks John - you're s a scholar and a gentlemen
cheers
cv
Thanks John for all the details & guidance you have provided - I think as you can see from the volume of replies that there is a big interest in this unique pre-amp.
I'm going to try this circuit integrated into a "Baby Huey" power amp & later a Zeus amp. Two quite dissimilar but also unqique designs.
I'm wondereing how this Voltage Regulator can be scaled up for a power amp as I thought of using it for both duties - preamp & poweramp VR?
I know there are high voltage/high power Mosfets available such as 350V/12A FDPF12N35 for reasonable prices (digikey $1) but how would LND150 be made suitable?
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