Sunday, April 27, 2014

"Parley" - valve preamp with jFet buffer

This build is to replace a single stage valve preamp with a jFet buffer\driver stage. This allows a  simple valve preamp to drive low impedance loads. The frontend is a 12AU7 plate follower with moderate gain and the back-end a Pass inspired B1 buffer. The buffer stage uses two jFet with one acting as a constant current source. Either stage could be used by itself but together you get the better of two worlds. I called this preamp "Parley".

The enclosure is a 2U 19”, black stippled rackable. Four modules: 250VHT\12VDC reg, 18VDC for buffer stage and the valve preamp section. There are three selectable inputs on the rear and with Alps Blue Velvet pot and 4oz solid brass knob the build is stylish and good sounding. It also compliments my tube and chip amp, “Number 9” which is in a similar enclosure and from both the front and back look the same.