John Curl's Blowtorch preamplifier

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Main issue or not, a CMRR of 30dB is below standard for such a pretentious amplifier. If you do it, do it right, but not this way.
Also the distortion of the input buffer is to high for such an amp.
I get 38ppm (with 2SK170-BL). While the rest of the amp is symmetrical/complementary, to me it's a great mystery why that buffer has not been made the same way. Ten times lower distortion at the expense of only two additional jfets and two resistors.
 
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quote
Anyone can use an opamp.

PMA, in my experience, using op-amps can be easier than discretes generally, but I'd say to get the best out of an op-amp, you need top know how to use them. There are too many cases where I see sloppy layout, not enough decoupling, using non-unity gain stable OPA's in 0dB gain applications (then they try to fix it by 'slugging' the feedback loop) etc. Discretes have their place, but I don't believe 'anyone' can use an op-amp and necessarily get good results.

One other point to be considered is that OPA's have come along way - thankfully we are not dealing with 741 type devices anymore (however, does anybody remember the 'Texan' amplifier based on - I think - a 741 opamp and CFP output stage - I'd love to look at that circuit again for nostalgic reasons - from the 1970s').
 
john curl said:
Very good Edmond, you get a gold star. You are only off by a factor of 2 or so, due to the amplitude loss across the fet follower, itself. Fire up the simulators gentlemen, and get me an exact value. Cap value changes are OK, as well

I didn't specify the input buffers at all. So what are you talking about? Of course, 3k43 is a theoretical value for buffers with Zo=0.
 
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