{"id":365,"date":"2011-09-11T09:59:21","date_gmt":"2011-09-11T13:59:21","guid":{"rendered":"http:\/\/hackaweek.com\/hacks\/?p=365"},"modified":"2011-09-11T09:59:21","modified_gmt":"2011-09-11T13:59:21","slug":"jfet-audio-preamp-with-piezo-guitar-pickup","status":"publish","type":"post","link":"http:\/\/hackaweek.com\/hacks\/jfet-audio-preamp-with-piezo-guitar-pickup\/","title":{"rendered":"JFET Audio Preamp with Piezo Guitar Pickup"},"content":{"rendered":"

I’ve been on a transistor theme here lately and there’s one more I’d like to cover, the JFET. JFET stands for Junction Field Effect Transistor<\/a>. These transistors are well suited for high impedance inputs and since a Piezo electric device<\/a> measures in the multi-megohm range it’s a perfect match.<\/p>\n

I found the schematic for this circuit on this webpage: Design Guidelines for JFET Audio Preamplifier Circuits By Mike Martell<\/a> Thanks Mike! Great write up. <\/p>\n

After some bread boarding and testing I decided this would be a great preamp for a Piezo pickup mounted inside my acoustic guitar. I salvaged a Piezo element from a Roomba vacuum I had in the scrap pile. They use them as a dirt sensor mounted above the rotating brushes as you’ll see in the video. <\/p>\n

I glued the Piezo element inside the guitar on the sound board near the sound hole and connected it to a 1\/4″ audio jack that I mounted on the lower body side. It sounds great but there is a bit of 60 cycle hum getting in the signal. I’m assuming that this is coming from the circuit being on a bread board. I plan on mounting the components to a PCB and finding a suitable metal enclosure to put it all inside of. I think the metal will help shield outside noise. <\/p>\n

This is a pretty easy project to put together. You can get JFETs from most electronics suppliers. I got mine from Tayda Electronics<\/a> for $.25 each. <\/p>\n

Keep on hackin!<\/p>\n

Parts List:<\/strong><\/p>\n

1 – 10 ohm resistor
\n1 – 470 ohm resistor
\n1 – 1.2K ohm resistor
\n1 – 1 Meg ohm resistor
\n1 – .1 uF polarized capacitor
\n1 – 2 – 4.7 uF polarized capacitors
\n1 – 100 uF polarized capacitor
\n1 – J201 Transistor<\/p>\n

Schematic:<\/strong><\/p>\n

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