I just had a good lesson on piezo installation from my freind Rob, who is an electronics wiz. I was getting a lot of buzz and hum from the piezo I had installed under the stainless steel cat food dish reso on my latest build. He had a look inside and had it figured in 30 seconds. First I was using the wrong kind of piezo, stainless steel with two sensor areas and missing a ground. I picked this out of my electronics box and hadn't noticed the two concentric sensor areas and mistook one lead for a ground. He told me the ground would be on the exterior metal ring and as stainless would be hard to solder with my equipment he pulled a brass one out of his tool box. Another thing I didn't know was, you should ground the black lead by soldering it at one end to the shielding wire, the uncoated wire inside your shielded audio cable. He soldered it to the jack end. He also pulled that portion back into the cable after shrinking the heat shrink tubes with a lighter to prevent shorting and improving the shielding against RF, which causes buzz. Next he demonstrated his impeccable soldering technique on the brass piezo. Soldering the ground on the outer ring is a snap as long as it doesn't contact the ring; he tinned all the wires prior to soldering them to the jack and piezo. Soldering to the silvered sensor area is a bit more difficult as the silver contact over the ceramic is easily damaged by overheating. Rob's technique involved unplugging the soldering iron until it just melted the solder before trying to apply a blob to the center of the sensor. He also considered strain when cutting the shielded cable wires, cutting them exactly where they need be. We tested the piezo by plugging into the amp and satisfied it was working, I glued it to the bottom of the cat dish. I waiting for the glue (E6000) to dry but I'm confident this was the fix. Hopefully this post will help someone out there. Let me know. Ken
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