Comment by easygenes
4 days ago
You can go further and replace the cheap Pi oscillator crystal with a proper TCXO, as others using them for NTD have done and documented: https://raspberrypi.stackexchange.com/questions/74482/switch...
That should give you 4-5x less drift than his results (though you could pair the techniques for even better figures)
Believe me, I have read that post/comment quite a few times. There are actually Pi 4 hats for sale for audiophiles (that seem to believe that you need 54000000.000 MHz system clock or whatever it is for Pi4 (Pi3 is 19.2 MHz) for optimal audio) that have an OCXO on them. But in another comment I said I'm not sure my soldering skills are that good.
I didn't think I was good at soldering until I invested in a good soldering workstation. That is:
* A microscope with a good working distance, and a large screen.
* A soldering iron with very short grip to tip distance. Miniware TS1M with 210/245 tips is a good choice.
* Some proper jigs to hold things. (Stickvise, sliding magnet plates)
* Good extraction so I don't worry about fumes. (Setting up over a stove range hood is great in a pinch)
Also just watching some of the soldering masters at work: https://www.youtube.com/@ycs-yang/videos
I don't have heaps of experience or the steadiest hands, but I'd be comfortable doing a mod like this cleanly now. One good tip is to get your work piece in a position where you can securely rest the blade of your hand on the table or something secure. You want to minimize the leverage and distance between a secure rest point and your work tip.
I mean you made an OCXO in a way. Why bother buying one? If you cold more tightly couple the temperature of the CPU and the crystal you'd be set.
And TCXOs are surprisingly cheap. Less than $2 when I looked at some of Abracon's offerings.