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Contained here are all my observations with this amp.
1) The schematic the DIYAUDIO Store PCB is based on does not allow 2nd harmonic adjustment through changing source resistor values.
2) The PCB circuit can be changed to the original degenerating circuit by moving cap leads to other side of resistor lead. This will restore 2nd harmonic adjustment through source resistance modification.
3) Output impedance also appears to be significantly affected (only tested in simulation).
4) As an alternative to the PCB mod, 2nd Harmonic adjustment can be altered on PCB circuit by selecting devices with different transconductance curves if one does not want to modify the PCB.
5) As an alternative to performing transconductance measurements and selecting non-matched devices for 2nd harmonic addition, installing one IRFP250 and one IRFP240 per channel will also give a dominant 2nd harmonic.
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