last weekend I built this rather simple yet effectice preamp for a piezo electric pick up. I came across this idea of amplyfing minute signals from a piezo disk from a youtube video. I do not own this schematic or idea. It belongs to one of my inspirations: Collin Cunningham.
The MPF-102 N-channel FET Rf amplifier is becoming obsolete and hard to find. I figured there must be a way to acheive such acoustic clarity with a more standard discrete semicunductor. Does anybody know what changes I could make?
This is a great circuit and works like a charm. Please pass it on
In this circuit the BFR30 (Digikey 568-6203-2-ND) should be a suitable replacement for the MPF-102, with some resistor value changes. Here are the three parameters that matter most in this application, compared.
BFR30 vs MPF-102
Zero Vgs drain current 4-10 mA vs 2-20 mA
Transconductance 1000-4000 uS vs 2000-7500 uS
gate cut-off voltage -5 V max vs -8 V
Because the BFR30 has lower minimum transconductance I would increase the drain resistor to 3k ohms. Based on the Fig. 6 I would make the source resistor 750 ohms.
I know very little and about circuits, parts, and how it all works.
On the other hand, sometimes I might remember something someone told me, and he could be genious, who knows.
I found it was hard to get MPF102's and was referred to the NTE457
zero vgs drain current: 1-5ma
transconductance: 1000-5000 uS
gate cut off voltag: - 6v max
I would like to try this circuit as a pick up for my acoustic guitar