I thought I'd take a moment to document what changed in the design since version 1.4.

For the TCXO variant board the only change has been the addition of footprints for what are effectively no-stuff parts at present. An 0805 layout for a capacitor in parallel with the feedback resistor of the OP amp is present, and footprints for an RC low-pass filter on the output of the amp has been added as well. But both of the new caps are no-stuff and the resistor of the low-pass filter is intended to be 0 ohms. The intent of both was to enable further bandwidth reduction of the control voltage path.

So, in short, the 1.5.2 board is merely a physical re-arrangement of the 1.4 design to fit into the new extruded aluminum case.

The 1.6.1 board is the design for the OH300 OCXO. For that design, the same extra parts are present on the board as the TCXO variant, but they are also no-stuff (for the caps) or 0 ohms (for the resistor). The feedback of the resistor is 82k instead of 51k. This is because the tuning range of the oscillator is much closer to the lifetime tolerance rating than the DOT050V, so we can't "throw away" quite as much of the voltage range.

But the big change is the use of the SC189Z buck converter instead of the LDO. The SC189Z is configured with a 2.2 µH inductor and 10 µF ceramic caps on both the input and output. Additionally, there's a footprint for a high value tantalum filter cap on the input to further filter, plus a 0.01µF cap on the output to try and further drive down the switching noise.

The downside of the SC189Z is that it has a maximum input voltage of 5.5V, so it means specifying a 5 volt supply. It turns out that DigiKey stocks a nice one, though. It's rated for 1.5A output current and it appears to me to have around 40 mV P-P of ripple under load (with the OH300 variant), which is not bad for a wall wart, and doesn't impact the output ripple on the 3.3 volt rail. Using it for the TCXO version works as well, and means that the LDO has just a little bit less heat to dissipate (compared to feeding it 6V or more).

I tried an alternate OP amp for the OH300 prototype, but it was a disaster - it oscillated badly. Going back to the AD8691 fixed that, though, so no more fooling around with that.