I was taking Lars’ advice from the reference designs post
A 4 layer PCB isn’t significantly more expensive, just an extra consideration.
Ive not done a PCBA order with JLCPCB yet, but it doesn’t have to be parts that are in stock. They just have to be able to order them from a distributor that will ship to mainland China. Did a quick search for the ADA4851 using their global parts sourcing and they have distrubtors with the chips in stock. Then you consign a quanty to them (need a few extra for wastage) and they will hold any excess in stock for you for free, that only you can use. I have even been able to get them to add a part that wasn’t in their database, they just need to check they can get them and read the datasheet to make sure they can assemble them.
So this topic partly comes from me intending to redo the Cadet series, maybe even the sync generator if I can sort out the clock issues. For the PCBs that require sync I intend to have both sync options - a rear phono sync input using an LMH1980 and the ribbon cable from the C1 sync gen, selectable via a jumper.
I am leaning toward making it all -+5v anyway, making the video op amps with a combined DIP8/SOIC8 footprint. Protect any inputs with diodes. Then if I want to do a sub assembly with eg a TSSOP to DIP8 in the future the circuit is ready. Doing it this way is probably the most versatile as it means it will be easier to use alternative parts. I will probably prototype with both the LM6172 and the TL972 since it is so much cheaper and being DIP easy to work with.
I don’t like diptrace so I am in the process of redrawing PCBs. Probably starting with ramp generator first as I think its the least complex board that requires sync - want to test out the dual sync jumper idea.