I recently purchased the JC-2 preamp kit that tubeshunter is selling on eBay. I made some changes to the stock component values to improve performance and reliablility. I also increased the gain to a little over 20 dB.
The kit I purchased did not have idss matched jfets. I had several of the JFETs on hand and selected idss matched parts. The differential pairs were matched to 0.1 mA, and the n and p channels were as close as possible. It will work without matching the fets, but the offset and distortion will be higher.
It is stable into 1000 pF capacitive loads, and has a THD of .001% in the audio band.
If you assemble this kit, be sure to test the bipolar transistors. The ones I received had their pin out reversed from the silk screen shown on the board. The picture on the eBay listing shows them inserted reversed as well.
I hope someone finds this of some use.
The kit I purchased did not have idss matched jfets. I had several of the JFETs on hand and selected idss matched parts. The differential pairs were matched to 0.1 mA, and the n and p channels were as close as possible. It will work without matching the fets, but the offset and distortion will be higher.
It is stable into 1000 pF capacitive loads, and has a THD of .001% in the audio band.
If you assemble this kit, be sure to test the bipolar transistors. The ones I received had their pin out reversed from the silk screen shown on the board. The picture on the eBay listing shows them inserted reversed as well.
I hope someone finds this of some use.