The recording equpment, v. 5 – a factory crystal of the late 1950s made of some compressed powder (barium titanate?) was used in recording system until recently. A common vintage piezo crystal consists of two plates, folded in the same planes together and wrapped in paper to give them strength. Factory crystal elements are always doubled and connected so that the external interference at the output is subtracted, and the amplitude of the useful signal increases. Technically, dual piezo pickups have only advantages, but subjectively they sound less clear than single-ended ones, just as a push-pull amplifier stage (PP), with other things being equal, sounds less clear than a single-ended (SE) one.
A couple of years ago, by inertia, I made my first homemade crystals symmetrical (see article Handmade Rochelle Salt piezo cartridre). Compared to the factory crystals of the 1950s, they sounded too cold. This was a predictable result, since the crystals were grown from modern salt, whereas for a full-fledged sound, it was necessary to make Rochelle salt yourself. I am not a bit of a chemist and the experiment has been shelved, but after several years, the chemist-enthusiast needed to complete the project was not found, and it was not possible to obtain good Rochelle salt. Only then I came up with the idea to make a single crystal instead of a double crystal and try to beat the vintage barium titanate with the improved clarity of the modern SE crystal and the precise Vector orientation of the cartridge components in the assembly.
I still failed to reach the warmth level of the vintage 1950s, although due to manual processing and homemade varnish I managed to raise it to an acceptable level. As for the other, the SE-crystal sounded not only more Clear, but also more broadband. As a result, it was decided to leave a homemade crystal in the recording system, do several digitizations, and make the final verdict later on a cold head.
Here is Video of crystal sawing, for more information, see Handmade Rochelle Salt piezo cartridre.