linuxguru buffer redux and beyond

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diyAudio Member RIP
Joined 2005
finally something in breadboard

I finally had a pressing need for a buffer prefacing a discrete CFA used in the inverting mode. By tight layout and using one BF862 and a slightly different current source, a ZVP3306 and a ZVN2106, no ferrite beads are needed. I mounted the 862 on short #20 bus wire leads arranged on a 0.1" grid protoboard. Using adapter boards or sockets adds too much stray inductance.

As shown in sim a lot of the distortion is occurring at the input due to the ZVP3306 gate capacitance. Although it is not bad, the worst-case condition is buffering a 5k potentiometer, hence as much as 1.25k at half-position. Although the distortion is still low, with a lower source resistance it dips down to about my Ap residual. I'm running with +/- 20V rails. I need additional preamplification to see the actual output noise, as it is well below the ~1.2uV rms of the Ap.

I would show more details but this is paying work for a client.
 
Brad, thanks for the update - I'm tempted to revisit this again in due course.

On a vaguely (un)related note, I listened today to an OPA4227 (quad OPA227) as a source-level unity-gain buffer with +/- 15V rails. For its modest specs, the transparency, detail and neutrality are jaw-dropping. No hash, no hiss, extremely dark and laid-back. It's great for an inexpensive universal tone-control, for those who're inclined to use tone-controls.
 
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