Hi Curtis, thank you very much for your detailed comments.
I wanted to ask, if you use COTS or custom RF cans and how you route the land vias, in the nanovolt thread, but didn't want to pollute the discussion with mundane detail.
In your research - did you find any makers of (fence and lid style) RF shields who can manage custom dimensions, in prototype quantities?
I should search on the manufacturers you list - Orbel, Lazerlok, Laird to see if they offer custom services.
To improvise - I did a Freecad step/dxf model for 0.8mm mild-steel sheet, and had it fabricated to try to prove the concept.
This approach should be OK for the larger LF magnetic (and thermal) guard cover, but is the wrong thickness for a rf-can.
I found a source of pre-tinned (for solderability) mild-steel in 0.2mm and 0.3mm thickness, but need to find a (local) service who can cut and fold the thinner metal.
Being able to pop the lid for access is probably needed as you note.
At this point, there's a trade-off between money spent on custom fabrication, versus extra time routing the pcb to accomodate fixed dimensioned parts.
The simultaneous aspect of mechanical design is a challenge.
The performance of the shields on the boards is quite good. I have used a sniffer probe made with five turns of magnet wire amplified 25x with two ADA4896 stages (about 30 MHz bandwidth) to get a qualititative feel for EMI around the board.
Using EMI sniffer probes and then doing experiments, switching between a bench supply and DC/DC converter is a really good idea.
Perhaps small electric and/or magnetic probes could be made a permanent (pcb) feature, that remain under the RF cans?
So the probes would route and present to a DUT connection header outside of the shield can.
I purchased a set of near field probes to try to get a bit familiar with doing EMI tests, but there's no way to use them with the cans fitted.
For the stackup, I used a 6-layer 1.2 mm board with the JLC2116 stackup.
Are there advantages in using JLC2116 versus other stackups, or even a basic manufacturing stack-up?
It seems like a good thing, if everything is well defined from a manufacturing pov.
Perhaps routing the fast digital signals (spi, adc control) with controlled impedance might reduce radiated emi, even if there are no timing/reflection needs.
For the dmm board, there are inner and outer layer grounds to shield (capacitive, magnetic) mostly orthogonal traces.
For the amplifier there are soic-8 footprints for jfe2140, and lsk389.
There is also a footprint for if3602.
I noted your comments about the thermal wander of the if3602 from the DIY cascode jfet lna thread,
So there is a 4-cycle sample acquisition sequence, that can measure and compensate the amp gain, against a small reference-voltage.
But use of if3602 is more in view as an alternative configuration like HP 34420a, rather than a general DMM and is not a priority.
Following Kleinstein's suggestion, I did some Allan variance noise tests with the jfe2140, posted in this thread, but still need to do it for the other parts.
I don't remember the numbers, but in a separate LNA project that I modeled a lot after your initial discrete jfet LNA design, I found lsk389 to be lower noise than jfe2140, but higher leakage (to be expected).
But shielding really needs to be improved first to gain confidence.
For supplies - at least for a first pass - I want to see if the design can be managed without dc/dc converters - and AZ ops for that matter.
I believe Shahriar Shahramian uncovered issues with the DMM7510 - even with the super low-coupling transformer used in that design.
I suspect fast voltage transitions on the rectifiers are a problem.
Adding LC filtering after rectification re-introduces coupling capacitance on the inductors.
So power supply issues are pushed-out as separate scope.
As fallback, I have a simple open-loop fixed-freq. push-pull, and resonant llc with zcs to test on a board, but they are a bit basic.
So for a power supply at the moment - the board can run with a scavenged 34401a mains-transformer (power input headers are designed to match).
Although this transformer is inadequate - with higher than expected coupling-capacitance and lack of a proper screen guard.
I did an experiment stuffing a small sheet of copper, between the two bobbins of Bel signal transformer, as a makeshift guard.
And this already works to reduces coupling (3x reduction from memory) better than the 34401a transformer, so it may something to explore.
If EMI can be measured qualitatively following your approach - with some sniffer probes. then trying out different supplies should be more of an option.