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Old 9th May 2012, 03:15 AM   #11
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Location: Silicon Valley
An interesting convolution - I'll have to redraw it (always a good first step for understanding an unfamiliar circuit) and stare at it a bit, but the designer looks as if he is taking advantage of the high gm of the bipolar to squeeze all the juice out of a single SRPP gain stage. I have a long thread on jfet srpp in this forum, with more modest gain per stage.

In this particular preamp, I'm taking advantage of the lowish impedance of the second amp stage to optimally load a hotly biased (~10 ma) PN4393 first stage. In this first incarnation, the impedance is a little high on the second stage feedback network, and it looks like I can reduce it considerably for optimal performance (at least, by what PSpice says) for the first stage, and lower noise for the second half. Part of this exercise will be to check PSpice against what a real analyzer says, and also, what the listening characteristics will be like for this circus freak/chimera.
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Old 10th May 2012, 06:52 AM   #12
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In the jfet SRPP thread (accessible right here in the "analog source" forum), I took a brief look at SRPP preamps using high gm jfets (they had a lot of gain). The circuit that teiffbassuebertr links to a couple of posts previous might be interesting using some high gm jfets in SRPP with equalization applied in-stage , and some modest amplification/buffering afterwards.

Right, he said - yet another project when my bench is already littered with stuff yearning towards completion. Well, as far as I have heard, no one has taken a hammer and broken all those busy little fingers out there (well, they should be busy), so they can take a look at the posited bipolar circuit and transpose it into jfet-land, mayhaps losing some nasty electrolytics along the way. What? You're waiting until I do it and offer a kit with parts and all that ? Ha! You'll be waiting quite a while, then... Call it a taunt, call it a challenge, call it anything you like. Start a thread.

Last edited by wrenchone; 10th May 2012 at 07:17 AM.
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