I had this box that needed a small circuit and one that would work with the +/-12volt battery supply. It used to be an EVS passive preamp. So, I put a JFET buffer similar to Nelson Pass' B1 Buffer in it.
It uses a dual rail supply which allows for the elimination of the coupling caps. I put a trim pot at the output to adjust DC offset. If I want I could eliminate the pot in the future by replacing it with a 10 ohm resistor paralleled with two larger value resistors that form a voltage divider.
Also, to make the DC offset pot work at the output you need to measure the Idss of the JFETs and have the lower Idss JFET as the current source, otherwise the other JFET is biased higher that Idss, with a gate to source voltage that is positive. This is a problem because it results in a negative DC offset, and the potentiometer can only make the output DC voltage less positive, not more positive.
Anyway, there it is. Oh yeah, the 1k gate stopper on the current source is not there. I did the current source just like Pass' B1, with the gate shorted to the source.
One reason I wanted to do this is because it will be the building block for my discrete JFET crossover for my dipole speaker project. So, thought I would give it a listen in our current system.
It uses a dual rail supply which allows for the elimination of the coupling caps. I put a trim pot at the output to adjust DC offset. If I want I could eliminate the pot in the future by replacing it with a 10 ohm resistor paralleled with two larger value resistors that form a voltage divider.
Also, to make the DC offset pot work at the output you need to measure the Idss of the JFETs and have the lower Idss JFET as the current source, otherwise the other JFET is biased higher that Idss, with a gate to source voltage that is positive. This is a problem because it results in a negative DC offset, and the potentiometer can only make the output DC voltage less positive, not more positive.
Anyway, there it is. Oh yeah, the 1k gate stopper on the current source is not there. I did the current source just like Pass' B1, with the gate shorted to the source.
One reason I wanted to do this is because it will be the building block for my discrete JFET crossover for my dipole speaker project. So, thought I would give it a listen in our current system.
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