For SMD, Shugart 1000, MFM and ESDI drives the raw signal is right there on the connectors, the controller does the a/d and sampling. This is why some controller cards are much better at reading disks than others. Degraded servo tracks on non-stepper motor drives are usually the problem here.

For IDE and up you do have to do a bit of surface mounted troubleshooting to find the head output from the Op-Amps but it's do-able. Now the professionals will open the disk in a clean room then remove the platters and read them with custom heads. Also remember you don't have to get the whole disk you just need to find the file of the wallet.dat. Even part of it would go a long way, and with things like a 256 bit ECC code you can probably compute out the missing bits with a lot of CPU power.

I like screwing with this stuff, keeps me out of trouble. The ironkey would be a lot harder IMO: