I’ve been using a mechanic’s stethoscope to monitor first and second crack on the Bullet R2 with very good results, so I wanted to share my setup in case it helps others.
I know this concept has been mentioned before, but here are the specifics of what I’m doing.
I started with a Lisle 52750 Dual Purpose Stethoscope Kit (about $27 on Amazon). I cut the stainless probe down to roughly 2 inches. That shortened probe is then inserted into a high-temp silicone tapered stopper (20mm). The stopper kit I used was a generic high-temp silicone plug set (around $10). I drilled a small hole through the stopper to create a tight, friction-fit seal around the probe.
The stopper is then seated directly into the trier port.
This creates a clean acoustic path into the drum without picking up excess mechanical noise from the chassis. The result is excellent—I can clearly hear both first and second crack, even on beans that typically have a very faint or subtle crack.
Simple, inexpensive, and very effective.