I think I have the Cherry paper.
For unbalanced outputs moving the output return current to a better location reduced its modulation of the LM78L12/79L12 ground references.
I drew what I wanted on the schematic but didn't route it that way on the Protoboard.
What I did find is that most of the HD2 was due to 5532 load current when driving balanced loads.
Balanced loads don't return current to ground - they feed current into the opposing output - so I turned my attention to the 5532's supply pins.
A 470 uF capacitor connected differentially at the 5532's supply pins (from Vcc to Vee) virtually eliminates HD2.
Some of this is likely due to parasitic resistance in the Protoboard but I'm going to put a big honkin' cap at the device pins anyway.
At less than +16 dBu balanced into 600Ω the distortion is <-140 dBc.
+18 dBu balanced 600Ω load is -138.9 dBc (all HD3). This is 63 mW into the 600Ω load - the 5532 is delivering 126 mW. (+24 dBu into 1200Ω. There are 2X 301Ω build-outs.)
+20 dBu balanced 600Ω load is -134.2 dBc (all HD3). 100 mW into 600Ω; 5532 200 mW.
+26 dBu balanced into an open circuit is -142.9 dBu. (About even HD2/HD3.)
I think the remaining distortion is mostly related to 5532 output stage linearity.
It's good enough that I don't want to add a buffer.
One thing that's really good about this oscillator is that the output level is set by a DC current.
The useful range is about -12 dBu to +26 dBu.
I found a really nice old 20 turn wirewound pot that I'm using to set level.
It's pretty easy to dial level in to 0.01 dB and the tempco is pretty low.
I see level drift of about +/-0.02 dB with typical room temperature variations.
Here's the latest schematic:
Updated schematic 1/8/21
Large: https://proaudiodesignforum.com/images/ ... ropped.png