http://beavishifi.com/projects/JFET_preamplifier/I read the original article with the provided link, and was I tempted to make some devilish remark to several of the original author's conjecture. But I feel like a saint tonight, kaya behave muna ako. Let me just suggest some mild additions to the circuit to improve one's chance of making it work in a more predictable way:1. Add at least >100uF capacitor to decouple the power supply. Better still, add another 0.1uF in parallel with the 100uF. This becomes even more important if you use battery with the circuit as the author strongly recommends. The reason is, the battery effective series resistance, which goes up as the battery ages, will create an unwanted signal path between the output and the input. Without power supply decoupling, there is a likelyhood the whole circuit will oscillate (i.e. motorboating and/or HF oscillation). For sure you do not want this to happen in your circuit.2. Add input coupling capacitor, even when the author says it is not necessary. 3. It seems the author picked an RF JFET only for reasons of availability. In fact, it is primary designed as a switch as per datasheet. If you want a preamp with low noise floor and good linearity, an RF device (or switch) is not exactly an excellent choice. If you could get hold on one (JFET) that is designed for audio, the added inconvenience of experimenting with the bias may well be worth it.
good advise......napasin ko ang title ng thread ay "First Watt B1 buffer preamp" i know this was a Nelson Pass design so this is the proper link: http://www.enjoythemusic.com/diy/0708/first_watt_b1_preamplifier.htmand scheme:
I read the original article with the provided link, and was I tempted to make some devilish remark to several of the original author's conjecture. But I feel like a saint tonight, kaya behave muna ako.
there is a mistake in the drawing, C1 and C2 is just 1 cap and connects to the + and - terminals of the bridged diodes....16volts ac input means an unloaded rail of 22.4 volts, as it is, zener current is about 22mA without anything connected to the psu terminals, actually less if we consider the dc resistance of hte power traffo...D3,R4,Q1 can be replaced with just a single 5watt zener diode.....